14.1. Making a high quality MPEG-4 ("DivX") rip of a DVD movie
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## 14.1. Making a high quality MPEG-4 ("DivX") rip of a DVD movie

One frequently asked question is "How do I make the highest quality rip for a given size?". Another question is "How do I make the highest quality DVD rip possible? I do not care about file size, I just want the best quality."

The latter question is perhaps at least somewhat wrongly posed. After all, if you do not care about file size, why not simply copy the entire MPEG-2 video stream from the the DVD? Sure, your AVI will end up being 5GB, give or take, but if you want the best quality and do not care about size, this is certainly your best option.

In fact, the reason you want to transcode a DVD into MPEG-4 is specifically because you do care about file size.

It is difficult to offer a cookbook recipe on how to create a very high quality DVD rip. There are several factors to consider, and you should understand these details or else you are likely to end up disappointed with your results. Below we will investigate some of these issues, and then have a look at an example. We assume you are using `libavcodec` to encode the video, although the theory applies to other codecs as well.

If this seems to be too much for you, you should probably use one of the many fine frontends that are listed in the MEncoder section of our related projects page. That way, you should be able to achieve high quality rips without too much thinking, because most of those tools are designed to take clever decisions for you.

### 14.1.1. Preparing to encode: Identifying source material and framerate

Before you even think about encoding a movie, you need to take several preliminary steps.

The first and most important step before you encode should be determining what type of content you are dealing with. If your source material comes from DVD or broadcast/cable/satellite TV, it will be stored in one of two formats: NTSC for North America and Japan, PAL for Europe, etc. It is important to realize, however, that this is just the formatting for presentation on a television, and often does not correspond to the original format of the movie. Experience shows that NTSC material is a lot more difficult to encode, because there more elements to identify in the source. In order to produce a suitable encode, you need to know the original format. Failure to take this into account will result in various flaws in your encode, including ugly combing (interlacing) artifacts and duplicated or even lost frames. Besides being ugly, the artifacts also harm coding efficiency: You will get worse quality per unit bitrate.

#### 14.1.1.1. Identifying source framerate

Here is a list of common types of source material, where you are likely to find them, and their properties:

- Standard Film: Produced for theatrical display at 24fps.

- PAL video: Recorded with a PAL video camera at 50 fields per second. A field consists of just the odd- or even-numbered lines of a frame. Television was designed to refresh these in alternation as a cheap form of analog compression. The human eye supposedly compensates for this, but once you understand interlacing you will learn to see it on TV too and never enjoy TV again. Two fields do not make a complete frame, because they are captured 1/50 of a second apart in time, and thus they do not line up unless there is no motion.

- NTSC Video: Recorded with an NTSC video camera at 60000/1001 fields per second, or 60 fields per second in the pre-color era. Otherwise similar to PAL.

- Animation: Usually drawn at 24fps, but also comes in mixed-framerate varieties.

- Computer Graphics (CG): Can be any framerate, but some are more common than others; 24 and 30 frames per second are typical for NTSC, and 25fps is typical for PAL.

- Old Film: Various lower framerates.

#### 14.1.1.2. Identifying source material

Movies consisting of frames are referred to as progressive, while those consisting of independent fields are called either interlaced or video - though this latter term is ambiguous.

To further complicate matters, some movies will be a mix of several of the above.

The most important distinction to make between all of these formats is that some are frame-based, while others are field-based. Whenever a movie is prepared for display on television (including DVD), it is converted to a field-based format. The various methods by which this can be done are collectively referred to as "pulldown", of which the infamous NTSC "3:2 telecine" is one variety. Unless the original material was also field-based (and the same fieldrate), you are getting the movie in a format other than the original.

There are several common types of pulldown:

- PAL 2:2 pulldown: The nicest of them all. Each frame is shown for the duration of two fields, by extracting the even and odd lines and showing them in alternation. If the original material is 24fps, this process speeds up the movie by 4%.

- PAL 2:2:2:2:2:2:2:2:2:2:2:3 pulldown: Every 12th frame is shown for the duration of three fields, instead of just two. This avoids the 4% speedup issue, but makes the process much more difficult to reverse. It is usually seen in musical productions where adjusting the speed by 4% would seriously damage the musical score.

- NTSC 3:2 telecine: Frames are shown alternately for the duration of 3 fields or 2 fields. This gives a fieldrate 2.5 times the original framerate. The result is also slowed down very slightly from 60 fields per second to 60000/1001 fields per second to maintain NTSC fieldrate.

- NTSC 2:2 pulldown: Used for showing 30fps material on NTSC. Nice, just like 2:2 PAL pulldown.

There are also methods for converting between NTSC and PAL video, but such topics are beyond the scope of this guide. If you encounter such a movie and want to encode it, your best bet is to find a copy in the original format. Conversion between these two formats is highly destructive and cannot be reversed cleanly, so your encode will greatly suffer if it is made from a converted source.

When video is stored on DVD, consecutive pairs of fields are grouped as a frame, even though they are not intended to be shown at the same moment in time. The MPEG-2 standard used on DVD and digital TV provides a way both to encode the original progressive frames and to store the number of fields for which a frame should be shown in the header of that frame. If this method has been used, the movie will often be described as "soft-telecined", since the process only directs the DVD player to apply pulldown to the movie rather than altering the movie itself. This case is highly preferable since it can easily be reversed (actually ignored) by the encoder, and since it preserves maximal quality. However, many DVD and broadcast production studios do not use proper encoding techniques but instead produce movies with "hard telecine", where fields are actually duplicated in the encoded MPEG-2.

The procedures for dealing with these cases will be covered later in this guide. For now, we leave you with some guides to identifying which type of material you are dealing with:

NTSC regions:

- If MPlayer prints that the framerate has changed to 24000/1001 when watching your movie, and never changes back, it is almost certainly progressive content that has been "soft telecined".

- If MPlayer shows the framerate switching back and forth between 24000/1001 and 30000/1001, and you see "combing" at times, then there are several possibilities. The 24000/1001 fps segments are almost certainly progressive content, "soft telecined", but the 30000/1001 fps parts could be either hard-telecined 24000/1001 fps content or 60000/1001 fields per second NTSC video. Use the same guidelines as the following two cases to determine which.

- If MPlayer never shows the framerate changing, and every single frame with motion appears combed, your movie is NTSC video at 60000/1001 fields per second.

- If MPlayer never shows the framerate changing, and two frames out of every five appear combed, your movie is "hard telecined" 24000/1001fps content.

PAL regions:

- If you never see any combing, your movie is 2:2 pulldown.

- If you see combing alternating in and out every half second, then your movie is 2:2:2:2:2:2:2:2:2:2:2:3 pulldown.

- If you always see combing during motion, then your movie is PAL video at 50 fields per second.

### Hint:

MPlayer can slow down movie playback with the -speed option or play it frame-by-frame. Try using `-speed` 0.2 to watch the movie very slowly or press the "." key repeatedly to play one frame at a time and identify the pattern, if you cannot see it at full speed.

### 14.1.2. Constant quantizer vs. multipass

It is possible to encode your movie at a wide range of qualities. With modern video encoders and a bit of pre-codec compression (downscaling and denoising), it is possible to achieve very good quality at 700 MB, for a 90-110 minute widescreen movie. Furthermore, all but the longest movies can be encoded with near-perfect quality at 1400 MB.

There are three approaches to encoding the video: constant bitrate (CBR), constant quantizer, and multipass (ABR, or average bitrate).

The complexity of the frames of a movie, and thus the number of bits required to compress them, can vary greatly from one scene to another. Modern video encoders can adjust to these needs as they go and vary the bitrate. In simple modes such as CBR, however, the encoders do not know the bitrate needs of future scenes and so cannot exceed the requested average bitrate for long stretches of time. More advanced modes, such as multipass encode, can take into account the statistics from previous passes; this fixes the problem mentioned above.

### Note:

Most codecs which support ABR encode only support two pass encode while some others such as `x264`, `XviD` and `libavcodec` support multipass, which slightly improves quality at each pass, yet this improvement is no longer measurable nor noticeable after the 4th or so pass. Therefore, in this section, two pass and multipass will be used interchangeably.

In each of these modes, the video codec (such as `libavcodec`) breaks the video frame into 16x16 pixel macroblocks and then applies a quantizer to each macroblock. The lower the quantizer, the better the quality and higher the bitrate. The method the movie encoder uses to determine which quantizer to use for a given macroblock varies and is highly tunable. (This is an extreme over-simplification of the actual process, but the basic concept is useful to understand.)

When you specify a constant bitrate, the video codec will encode the video, discarding detail as much as necessary and as little as possible in order to remain lower than the given bitrate. If you truly do not care about file size, you could as well use CBR and specify a bitrate of infinity. (In practice, this means a value high enough so that it poses no limit, like 10000Kbit.) With no real restriction on bitrate, the result is that the codec will use the lowest possible quantizer for each macroblock (as specified by `vqmin` for `libavcodec`, which is 2 by default). As soon as you specify a low enough bitrate that the codec is forced to use a higher quantizer, then you are almost certainly ruining the quality of your video. In order to avoid that, you should probably downscale your video, according to the method described later on in this guide. In general, you should avoid CBR altogether if you care about quality.

With constant quantizer, the codec uses the same quantizer, as specified by the `vqscale` option (for `libavcodec`), on every macroblock. If you want the highest quality rip possible, again ignoring bitrate, you can use `vqscale=2`. This will yield the same bitrate and PSNR (peak signal-to-noise ratio) as CBR with `vbitrate`=infinity and the default `vqmin` of 2.

The problem with constant quantizing is that it uses the given quantizer whether the macroblock needs it or not. That is, it might be possible to use a higher quantizer on a macroblock without sacrificing visual quality. Why waste the bits on an unnecessarily low quantizer? Your CPU has as many cycles as there is time, but there is only so many bits on your hard disk.

With a two pass encode, the first pass will rip the movie as though it were CBR, but it will keep a log of properties for each frame. This data is then used during the second pass in order to make intelligent decisions about which quantizers to use. During fast action or high detail scenes, higher quantizers will likely be used, and during slow moving or low detail scenes, lower quantizers will be used. Normally, the amount of motion is much more important than the amount of detail.

If you use `vqscale=2`, then you are wasting bits. If you use `vqscale=3`, then you are not getting the highest quality rip. Suppose you rip a DVD at `vqscale=3`, and the result is 1800Kbit. If you do a two pass encode with `vbitrate=1800`, the resulting video will have higher quality for the same bitrate.

Since you are now convinced that two pass is the way to go, the real question now is what bitrate to use? The answer is that there is no single answer. Ideally you want to choose a bitrate that yields the best balance between quality and file size. This is going to vary depending on the source video.

If size does not matter, a good starting point for a very high quality rip is about 2000Kbit plus or minus 200Kbit. For fast action or high detail source video, or if you just have a very critical eye, you might decide on 2400 or 2600. For some DVDs, you might not notice a difference at 1400Kbit. It is a good idea to experiment with scenes at different bitrates to get a feel.

If you aim at a certain size, you will have to somehow calculate the bitrate. But before that, you need to know how much space you should reserve for the audio track(s), so you should rip those first. You can compute the bitrate with the following equation: `bitrate = (target_size_in_Mbytes - sound_size_in_Mbytes) * 1024 * 1024 / length_in_secs * 8 / 1000` For instance, to squeeze a two-hour movie onto a 702MB CD, with 60MB of audio track, the video bitrate will have to be: `(702 - 60) * 1024 * 1024 / (120*60) * 8 / 1000 = 740kbps`

### 14.1.3. Constraints for efficient encoding

Due to the nature of MPEG-type compression, there are various constraints you should follow for maximal quality. MPEG splits the video up into 16x16 squares called macroblocks, each composed of 4 8x8 blocks of luma (intensity) information and two half-resolution 8x8 chroma (color) blocks (one for red-cyan axis and the other for the blue-yellow axis). Even if your movie width and height are not multiples of 16, the encoder will use enough 16x16 macroblocks to cover the whole picture area, and the extra space will go to waste. So in the interests of maximizing quality at a fixed filesize, it is a bad idea to use dimensions that are not multiples of 16.

Most DVDs also have some degree of black borders at the edges. Leaving these in place can hurt quality in several ways.

1. MPEG-type compression is also highly dependent on frequency domain transformations, in particular the Discrete Cosine Transform (DCT), which is similar to the Fourier transform. This sort of encoding is efficient for representing patterns and smooth transitions, but it has a hard time with sharp edges. In order to encode them it must use many more bits, or else an artifact known as ringing will appear.

   The frequency transform (DCT) takes place separately on each macroblock (actually each block), so this problem only applies when the sharp edge is inside a block. If your black borders begin exactly at multiple-of-16 pixel boundaries, this is not a problem. However, the black borders on DVDs rarely come nicely aligned, so in practice you will always need to crop to avoid this penalty.

In addition to frequency domain transforms, MPEG-type compression uses motion vectors to represent the change from one frame to the next. Motion vectors naturally work much less efficiently for new content coming in from the edges of the picture, because it is not present in the previous frame. As long as the picture extends all the way to the edge of the encoded region, motion vectors have no problem with content moving out the edges of the picture. However, in the presence of black borders, there can be trouble:

2. For each macroblock, MPEG-type compression stores a vector identifying which part of the previous frame should be copied into this macroblock as a base for predicting the next frame. Only the remaining differences need to be encoded. If a macroblock spans the edge of the picture and contains part of the black border, then motion vectors from other parts of the picture will overwrite the black border. This means that lots of bits must be spent either re-blackening the border that was overwritten, or (more likely) a motion vector will not be used at all and all the changes in this macroblock will have to be coded explicitly. Either way, encoding efficiency is greatly reduced.

   Again, this problem only applies if black borders do not line up on multiple-of-16 boundaries.

3. Finally, suppose we have a macroblock in the interior of the picture, and an object is moving into this block from near the edge of the image. MPEG-type coding cannot say "copy the part that is inside the picture but not the black border." So the black border will get copied inside too, and lots of bits will have to be spent encoding the part of the picture that is supposed to be there.

   If the picture runs all the way to the edge of the encoded area, MPEG has special optimizations to repeatedly copy the pixels at the edge of the picture when a motion vector comes from outside the encoded area. This feature becomes useless when the movie has black borders. Unlike problems 1 and 2, aligning the borders at multiples of 16 does not help here.

4. Despite the borders being entirely black and never changing, there is at least a minimal amount of overhead involved in having more macroblocks.

For all of these reasons, it is recommended to fully crop black borders. Further, if there is an area of noise/distortion at the edge of the picture, cropping this will improve encoding efficiency as well. Videophile purists who want to preserve the original as close as possible may object to this cropping, but unless you plan to encode at constant quantizer, the quality you gain from cropping will considerably exceed the amount of information lost at the edges.

### 14.1.4. Cropping and Scaling

Recall from the previous section that the final picture size you encode should be a multiple of 16 (in both width and height). This can be achieved by cropping, scaling, or a combination of both.

When cropping, there are a few guidelines that must be followed to avoid damaging your movie. The normal YUV format, 4:2:0, stores chroma (color) information subsampled, i.e. chroma is only sampled half as often in each direction as luma (intensity) information. Observe this diagram, where L indicates luma sampling points and C chroma.

L | L | L | L | L | L | L | L
C | C | C | C
L | L | L | L | L | L | L | L
L | L | L | L | L | L | L | L
C | C | C | C
L | L | L | L | L | L | L | L

As you can see, rows and columns of the image naturally come in pairs. Thus your crop offsets and dimensions must be even numbers. If they are not, the chroma will no longer line up correctly with the luma. In theory, it is possible to crop with odd offsets, but it requires resampling the chroma which is potentially a lossy operation and not supported by the crop filter.

Further, interlaced video is sampled as follows:

Top field | Bottom field
L | L | L | L | L | L | L | L |  |  |  |  |  |  |  |
C | C | C | C |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  | L | L | L | L | L | L | L | L
L | L | L | L | L | L | L | L |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  | C | C | C | C
|  |  |  |  |  |  |  | L | L | L | L | L | L | L | L
L | L | L | L | L | L | L | L |  |  |  |  |  |  |  |
C | C | C | C |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  | L | L | L | L | L | L | L | L
L | L | L | L | L | L | L | L |  |  |  |  |  |  |  |
|  |  |  |  |  |  |  | C | C | C | C
|  |  |  |  |  |  |  | L | L | L | L | L | L | L | L

As you can see, the pattern does not repeat until after 4 lines. So for interlaced video, your y-offset and height for cropping must be multiples of 4.

Native DVD resolution is 720x480 for NTSC, and 720x576 for PAL, but there is an aspect flag that specifies whether it is full-screen (4:3) or wide-screen (16:9). Many (if not most) widescreen DVDs are not strictly 16:9, and will be either 1.85:1 or 2.35:1 (cinescope). This means that there will be black bands in the video that will need to be cropped out.

MPlayer provides a crop detection filter that will determine the crop rectangle (`-vf cropdetect`). Run MPlayer with `-vf cropdetect` and it will print out the crop settings to remove the borders. You should let the movie run long enough that the whole picture area is used, in order to get accurate crop values.

Then, test the values you get with MPlayer, using the command line which was printed by `cropdetect`, and adjust the rectangle as needed. The `rectangle` filter can help by allowing you to interactively position the crop rectangle over your movie. Remember to follow the above divisibility guidelines so that you do not misalign the chroma planes.

In certain cases, scaling may be undesirable. Scaling in the vertical direction is difficult with interlaced video, and if you wish to preserve the interlacing, you should usually refrain from scaling. If you will not be scaling but you still want to use multiple-of-16 dimensions, you will have to overcrop. Do not undercrop, since black borders are very bad for encoding!

Because MPEG-4 uses 16x16 macroblocks, you will want to make sure that each dimension of the video you are encoding is a multiple of 16 or else you will be degrading quality, especially at lower bitrates. You can do this by rounding the width and height of the crop rectangle down to the nearest multiple of 16. As stated earlier, when cropping, you will want to increase the Y offset by half the difference of the old and the new height so that the resulting video is taken from the center of the frame. And because of the way DVD video is sampled, make sure the offset is an even number. (In fact, as a rule, never use odd values for any parameter when you are cropping and scaling video.) If you are not comfortable throwing a few extra pixels away, you might prefer instead to scale the video instead. We will look at this in our example below. You can actually let the `cropdetect` filter do all of the above for you, as it has an optional `round` parameter that is equal to 16 by default.

Also, be careful about "half black" pixels at the edges. Make sure you crop these out too, or else you will be wasting bits there that are better spent elsewhere.

After all is said and done, you will probably end up with video whose pixels are not quite 1.85:1 or 2.35:1, but rather something close to that. You could calculate the new aspect ratio manually, but MEncoder offers an option for `libavcodec` called `autoaspect` that will do this for you. Absolutely do not scale this video up in order to square the pixels unless you like to waste your hard disk space. Scaling should be done on playback, and the player will use the aspect stored in the AVI to determine the correct resolution. Unfortunately, not all players enforce this auto-scaling information, therefore you may still want to rescale.

### 14.1.5. Choosing resolution and bitrate

If you will not be encoding in constant quantizer mode, you need to select a bitrate. The concept of bitrate is quite simple. It is the (average) number of bits that will be consumed to store your movie, per second. Normally bitrate is measured in kilobits (1000 bits) per second. The size of your movie on disk is the bitrate times the length of the movie in time, plus a small amount of "overhead" (see the section on the AVI container for instance). Other parameters such as scaling, cropping, etc. will not alter the file size unless you change the bitrate as well!.

Bitrate does not scale proportionally to resolution. That is to say, a 320x240 file at 200 kbit/sec will not be the same quality as the same movie at 640x480 and 800 kbit/sec! There are two reasons for this:

1. Perceptual: You notice MPEG artifacts more if they are scaled up bigger! Artifacts appear on the scale of blocks (8x8). Your eye will not see errors in 4800 small blocks as easily as it sees errors in 1200 large blocks (assuming you will be scaling both to fullscreen).

2. Theoretical: When you scale down an image but still use the same size (8x8) blocks for the frequency space transform, you move more data to the high frequency bands. Roughly speaking, each pixel contains more of the detail than it did before. So even though your scaled-down picture contains 1/4 the information in the spacial directions, it could still contain a large portion of the information in the frequency domain (assuming that the high frequencies were underutilized in the original 640x480 image).

Past guides have recommended choosing a bitrate and resolution based on a "bits per pixel" approach, but this is usually not valid due to the above reasons. A better estimate seems to be that bitrates scale proportional to the square root of resolution, so that 320x240 and 400 kbit/sec would be comparable to 640x480 at 800 kbit/sec. However this has not been verified with theoretical or empirical rigor. Further, given that movies vary greatly with regard to noise, detail, degree of motion, etc., it is futile to make general recommendations for bits per length-of-diagonal (the analog of bits per pixel, using the square root).

So far we have discussed the difficulty of choosing a bitrate and resolution.

#### 14.1.5.1. Computing the resolution

The following steps will guide you in computing the resolution of your encode without distorting the video too much, by taking into account several types of information about the source video. First, you should compute the encoded aspect ratio: `ARc = (Wc x (ARa / PRdvd )) / Hc`

where:

- Wc and Hc are the width and height of the cropped video,

- ARa is the displayed aspect ratio, which usually is 4/3 or 16/9,

- PRdvd is the pixel ratio of the DVD which is equal to 1.25=(720/576) for PAL DVDs and 1.5=(720/480) for NTSC DVDs,

Then, you can compute the X and Y resolution, according to a certain Compression Quality (CQ) factor: `ResY = INT(SQRT( 1000*Bitrate/25/ARc/CQ )/16) * 16` and `ResX = INT( ResY * ARc / 16) * 16`

Okay, but what is the CQ? The CQ represents the number of bits per pixel and per frame of the encode. Roughly speaking, the greater the CQ, the less the likelihood to see encoding artifacts. However, if you have a target size for your movie (1 or 2 CDs for instance), there is a limited total number of bits that you can spend; therefore it is necessary to find a good tradeoff between compressibility and quality.

The CQ depends on the bitrate, the video codec efficiency and the movie resolution. In order to raise the CQ, typically you would downscale the movie given that the bitrate is computed in function of the target size and the length of the movie, which are constant. With MPEG-4 ASP codecs such as `XviD` and `libavcodec`, a CQ below 0.18 usually results in a pretty blocky picture, because there are not enough bits to code the information of each macroblock. (MPEG4, like many other codecs, groups pixels by blocks of several pixels to compress the image; if there are not enough bits, the edges of those blocks are visible.) It is therefore wise to take a CQ ranging from 0.20 to 0.22 for a 1 CD rip, and 0.26-0.28 for 2 CDs rip with standard encoding options. More advanced encoding options such as those listed here for `libavcodec` and `XviD` should make it possible to get the same quality with CQ ranging from 0.18 to 0.20 for a 1 CD rip, and 0.24 to 0.26 for a 2 CD rip. With MPEG-4 ASP codecs such as `x264`, you can use a CQ ranging from 0.14 to 0.16 with standard encoding options, and should be able to go as low as 0.10 to 0.12 with `x264`'s advanced encoding settings.

Please take note that the CQ is just an indicative figure, as depending on the encoded content, a CQ of 0.18 may look just fine for a Bergman, contrary to a movie such as The Matrix, which contains many high-motion scenes. On the other hand, it is worthless to raise CQ higher than 0.30 as you would be wasting bits without any noticeable quality gain. Also note that as mentioned earlier in this guide, low resolution videos need a bigger CQ (compared to, for instance, DVD resolution) to look good.

### 14.1.6. Filtering

Learning how to use MEncoder's video filters is essential to producing good encodes. All video processing is performed through the filters -- cropping, scaling, color adjustment, noise removal, sharpening, deinterlacing, telecine, inverse telecine, and deblocking, just to name a few. Along with the vast number of supported input formats, the variety of filters available in MEncoder is one of its main advantages over other similar programs.

Filters are loaded in a chain using the -vf option:

    -vf filter1=options,filter2=options,...

Most filters take several numeric options separated by colons, but the syntax for options varies from filter to filter, so read the man page for details on the filters you wish to use.

Filters operate on the video in the order they are loaded. For example, the following chain:

    -vf crop=688:464:12:4,scale=640:464

will first crop the 688x464 region of the picture with upper-left corner at (12,4), and then scale the result down to 640x464.

Certain filters need to be loaded at or near the beginning of the filter chain, in order to take advantage of information from the video decoder that will be lost or invalidated by other filters. The principal examples are `pp` (postprocessing, only when it is performing deblock or dering operations), `spp` (another postprocessor to remove MPEG artifacts), `pullup` (inverse telecine), and `softpulldown` (for converting soft telecine to hard telecine).

In general, you want to do as little filtering as possible to the movie in order to remain close to the original DVD source. Cropping is often necessary (as described above), but avoid to scale the video. Although scaling down is sometimes preferred to using higher quantizers, we want to avoid both these things: remember that we decided from the start to trade bits for quality.

Also, do not adjust gamma, contrast, brightness, etc. What looks good on your display may not look good on others. These adjustments should be done on playback only.

One thing you might want to do, however, is pass the video through a very light denoise filter, such as `-vf hqdn3d=2:1:2`. Again, it is a matter of putting those bits to better use: why waste them encoding noise when you can just add that noise back in during playback? Increasing the parameters for `hqdn3d` will further improve compressibility, but if you increase the values too much, you risk degrading the image visibily. The suggested values above (`2:1:2`) are quite conservative; you should feel free to experiment with higher values and observe the results for yourself.

### 14.1.7. Interlacing and Telecine

Almost all movies are shot at 24 fps. Because NTSC is 30000/1001 fps, some processing must be done to this 24 fps video to make it run at the correct NTSC framerate. The process is called 3:2 pulldown, commonly referred to as telecine (because pulldown is often applied during the telecine process), and, naively described, it works by slowing the film down to 24000/1001 fps, and repeating every fourth frame.

No special processing, however, is done to the video for PAL DVDs, which run at 25 fps. (Technically, PAL can be telecined, called 2:2 pulldown, but this does not become an issue in practice.) The 24 fps film is simply played back at 25 fps. The result is that the movie runs slightly faster, but unless you are an alien, you probably will not notice the difference. Most PAL DVDs have pitch-corrected audio, so when they are played back at 25 fps things will sound right, even though the audio track (and hence the whole movie) has a running time that is 4% less than NTSC DVDs.

Because the video in a PAL DVD has not been altered, you need not worry much about framerate. The source is 25 fps, and your rip will be 25 fps. However, if you are ripping an NTSC DVD movie, you may need to apply inverse telecine.

For movies shot at 24 fps, the video on the NTSC DVD is either telecined 30000/1001, or else it is progressive 24000/1001 fps and intended to be telecined on-the-fly by a DVD player. On the other hand, TV series are usually only interlaced, not telecined. This is not a hard rule: some TV series are interlaced (such as Buffy the Vampire Slayer) whereas some are a mixture of progressive and interlaced (such as Angel, or 24).

It is highly recommended that you read the section on How to deal with telecine and interlacing in NTSC DVDs to learn how to handle the different possibilities.

However, if you are mostly just ripping movies, likely you are either dealing with 24 fps progressive or telecined video, in which case you can use the `pullup` filter `-vf pullup,softskip`.

### 14.1.8. Encoding interlaced video

If the movie you want to encode is interlaced (NTSC video or PAL video), you will need to choose whether you want to deinterlace or not. While deinterlacing will make your movie usable on progressive scan displays such a computer monitors and projectors, it comes at a cost: The fieldrate of 50 or 60000/1001 fields per second is halved to 25 or 30000/1001 frames per second, and roughly half of the information in your movie will be lost during scenes with significant motion.

Therefore, if you are encoding for high quality archival purposes, it is recommended not to deinterlace. You can always deinterlace the movie at playback time when displaying it on progressive scan devices. The power of currently available computers forces players to use a deinterlacing filter, which results in a slight degradation in image quality. But future players will be able to mimic the interlaced display of a TV, deinterlacing to full fieldrate and interpolating 50 or 60000/1001 entire frames per second from the interlaced video.

Special care must be taken when working with interlaced video:

1. Crop height and y-offset must be multiples of 4.

2. Any vertical scaling must be performed in interlaced mode.

3. Postprocessing and denoising filters may not work as expected unless you take special care to operate them a field at a time, and they may damage the video if used incorrectly.

With these things in mind, here is our first example:

      mencoder capture.avi -mc 0 -oac lavc -ovc lavc -lavcopts \
      vcodec=mpeg2video:vbitrate=6000:ilme:ildct:acodec=mp2:abitrate=224

Note the `ilme` and `ildct` options.

### 14.1.9. Notes on Audio/Video synchronization

MEncoder's audio/video synchronization algorithms were designed with the intention of recovering files with broken sync. However, in some cases they can cause unnecessary skipping and duplication of frames, and possibly slight A/V desync, when used with proper input (of course, A/V sync issues apply only if you process or copy the audio track while transcoding the video, which is strongly encouraged). Therefore, you may have to switch to basic A/V sync with the `-mc 0` option, or put this in your `~/.mplayer/mencoder` config file, as long as you are only working with good sources (DVD, TV capture, high quality MPEG-4 rips, etc) and not broken ASF/RM/MOV files.

If you want to further guard against strange frame skips and duplication, you can use both `-mc 0` and `-noskip`. This will prevent all A/V sync, and copy frames one-to-one, so you cannot use it if you will be using any filters that unpredictably add or drop frames, or if your input file has variable framerate! Therefore, using `-noskip` is not in general recommended.

The so-called "three-pass" audio encoding which MEncoder supports has been reported to cause A/V desync. This will definitely happen if it is used in conjunction with certain filters, therefore, it is now recommended not to use three-pass audio mode. This feature is only left for compatibility purposes and for expert users who understand when it is safe to use and when it is not. If you have never heard of three-pass mode before, forget that we even mentioned it!

There have also been reports of A/V desync when encoding from stdin with MEncoder. Do not do this! Always use a file or CD/DVD/etc device as input.

### 14.1.10. Choosing the video codec

Which video codec is best to choose depends on several factors, like size, quality, streamability, usability and popularity, some of which widely depend on personal taste and technical constraints.

- Compression efficiency: It is quite easy to understand that most newer-generation codecs are made to increase quality and compression. Therefore, the authors of this guide and many other people suggest that you cannot go wrong [2] when choosing MPEG-4 AVC codecs like `x264` instead of MPEG-4 ASP codecs such as `libavcodec` MPEG-4 or `XviD`. (Advanced codec developers may be interested in reading Michael Niedermayer's opinion on "why MPEG4-ASP sucks".) Likewise, you should get better quality using MPEG-4 ASP than you would with MPEG-2 codecs.

  However, newer codecs which are in heavy development can suffer from bugs which have not yet been noticed and which can ruin an encode. This is simply the tradeoff for using bleeding-edge technology.

  What is more, beginning to use a new codec requires that you spend some time becoming familiar with its options, so that you know what to adjust to achieve a desired picture quality.

- Hardware compatibility: It usually takes a long time for standalone video players to begin to include support for the latest video codecs. As a result, most only support MPEG-1 (like VCD, XVCD and KVCD), MPEG-2 (like DVD, SVCD and KVCD) and MPEG-4 ASP (like DivX, `libavcodec`'s LMP4 and `XviD`) (Beware: Usually, not all MPEG-4 ASP features are supported). Please refer to the technical specs of your player (if they are available), or google around for more information.

- Best quality per encoding time: Codecs that have been around for some time (such as `libavcodec` MPEG-4 and `XviD`) are usually heavily optimized with all kinds of smart algorithms and SIMD assembly code. That is why they tend to yield the best quality per encoding time ratio. However, they may have some very advanced options that, if enabled, will make the encode really slow for marginal gains.

  If you are after blazing speed you should stick around the default settings of the video codec (although you should still try the other options which are mentioned in other sections of this guide).

  You may also consider choosing a codec which can do multi-threaded processing, though this is only useful for users of machines with several CPUs. `libavcodec` MPEG-4 does allow that, but speed gains are limited, and there is a slight negative effect on picture quality. `XviD`'s multi-threaded encoding, activated by the `threads` option, can be used to boost encoding speed — by about 40-60% in typical cases — with little if any picture degradation. `x264` also allows multi-threaded encoding, which currently speeds up encoding by 15-30% (depending on the encoding settings) while lowering PSNR by about 0.05dB.

- Personal taste: This is where it gets almost irrational: For the same reason that some hung on to DivX 3 for years when newer codecs were already doing wonders, some folks will prefer `XviD` or `libavcodec` MPEG-4 over `x264`.

  You should make your own judgement; do not take advice from people who swear by one codec. Take a few sample clips from raw sources and compare different encoding options and codecs to find one that suits you best. The best codec is the one you master, and the one that looks best to your eyes on your display [3]!

Please refer to the section selecting codecs and container formats to get a list of supported codecs.

### 14.1.11. Audio

Audio is a much simpler problem to solve: if you care about quality, just leave it as is. Even AC3 5.1 streams are at most 448Kbit/s, and they are worth every bit. You might be tempted to transcode the audio to high quality Vorbis, but just because you do not have an A/V receiver for AC3 pass-through today does not mean you will not have one tomorrow. Future-proof your DVD rips by preserving the AC3 stream. You can keep the AC3 stream either by copying it directly into the video stream during the encoding. You can also extract the AC3 stream in order to mux it into containers such as NUT or Matroska.

    mplayer source_file.vob -aid 129 -dumpaudio -dumpfile sound.ac3

will dump into the file `sound.ac3` the audio track number 129 from the file `source_file.vob` (NB: DVD VOB files usually use a different audio numbering, which means that the VOB audio track 129 is the 2nd audio track of the file).

But sometimes you truly have no choice but to further compress the sound so that more bits can be spent on the video. Most people choose to compress audio with either MP3 or Vorbis audio codecs. While the latter is a very space-efficient codec, MP3 is better supported by hardware players, although this trend is changing.

Do not use `-nosound` when encoding a file with audio, even if you will be encoding and muxing audio separately later. Though it may work in ideal cases, using `-nosound` is likely to hide some problems in your encoding command line setting. In other words, having a soundtrack during your encode assures you that, provided you do not see messages such as “Too many audio packets in the buffer”, you will be able to get proper sync.

You need to have MEncoder process the sound. You can for example copy the orignal soundtrack during the encode with `-oac copy` or convert it to a "light" 4 kHz mono WAV PCM with `-oac pcm -channels 1 -srate 4000`. Otherwise, in some cases, it will generate a video file that will not sync with the audio. Such cases are when the number of video frames in the source file does not match up to the total length of audio frames or whenever there are discontinuities/splices where there are missing or extra audio frames. The correct way to handle this kind of problem is to insert silence or cut audio at these points. However MPlayer cannot do that, so if you demux the AC3 audio and encode it with a separate app (or dump it to PCM with MPlayer), the splices will be left incorrect and the only way to correct them is to drop/dup video frames at the splice. As long as MEncoder sees the audio when it is encoding the video, it can do this dropping/duping (which is usually OK since it takes place at full black/scenechange, but if MEncoder cannot see the audio, it will just process all frames as-is and they will not fit the final audio stream when you for example merge your audio and video track into a Matroska file.

First of all, you will have to convert the DVD sound into a WAV file that the audio codec can use as input. For example:

    mplayer source_file.vob -ao pcm:file=destination_sound.wav -vc dummy -aid 1 -vo null

will dump the second audio track from the file `source_file.vob` into the file `destination_sound.wav`. You may want to normalize the sound before encoding, as DVD audio tracks are commonly recorded at low volumes. You can use the tool normalize for instance, which is available in most distributions. If you are using Windows, a tool such as BeSweet can do the same job. You will compress in either Vorbis or MP3. For example:

    oggenc -q1 destination_sound.wav

will encode `destination_sound.wav` with the encoding quality 1, which is roughly equivalent to 80Kb/s, and is the minimum quality at which you should encode if you care about quality. Please note that MEncoder currently cannot mux Vorbis audio tracks into the output file because it only supports AVI and MPEG containers as an output, each of which may lead to audio/video playback synchronization problems with some players when the AVI file contain VBR audio streams such as Vorbis. Do not worry, this document will show you how you can do that with third party programs.

### 14.1.12. Muxing

Now that you have encoded your video, you will most likely want to mux it with one or more audio tracks into a movie container, such as AVI, MPEG, Matroska or NUT. MEncoder is currently only able to natively output audio and video into MPEG and AVI container formats. for example:

    mencoder -oac copy -ovc copy  -o output_movie.avi -audiofile input_audio.mp2 input_video.avi

This would merge the video file `input_video.avi` and the audio file `input_audio.mp2` into the AVI file `output_movie.avi`. This command works with MPEG-1 layer I, II and III (more commonly known as MP3) audio, WAV and a few other audio formats too.

MEncoder features experimental support for `libavformat`, which is a library from the FFmpeg project that supports muxing and demuxing a variety of containers. For example:

    mencoder -oac copy -ovc copy  -o output_movie.asf -audiofile input_audio.mp2 input_video.avi -of lavf -lavfopts format=asf

This will do the same thing as the previous example, except that the output container will be ASF. Please note that this support is highly experimental (but getting better every day), and will only work if you compiled MPlayer with the support for `libavformat` enabled (which means that a pre-packaged binary version will not work in most cases).

#### 14.1.12.1. Improving muxing and A/V sync reliability

You may experience some serious A/V sync problems while trying to mux your video and some audio tracks, where no matter how you adjust the audio delay, you will never get proper sync. That may happen when you use some video filters that will drop or duplicate some frames, like the inverse telecine filters. It is strongly encouraged to append the `harddup` video filter at the end of the filter chain to avoid this kind of problem.

Without `harddup`, if MEncoder wants to duplicate a frame, it relies on the muxer to put a mark on the container so that the last frame will be displayed again to maintain sync while writing no actual frame. With `harddup`, MEncoder will instead just push the last frame displayed again into the filter chain. This means that the encoder receives the exact same frame twice, and compresses it. This will result in a slightly bigger file, but will not cause problems when demuxing or remuxing into other container formats.

You may also have no choice but to use `harddup` with container formats that are not too tightly linked with MEncoder such as the ones supported through `libavformat`, which may not support frame duplication at the container level.

#### 14.1.12.2. Limitations of the AVI container

Although it is the most widely-supported container format after MPEG-1, AVI also has some major drawbacks. Perhaps the most obvious is the overhead. For each chunk of the AVI file, 24 bytes are wasted on headers and index. This translates into a little over 5 MB per hour, or 1-2.5% overhead for a 700 MB movie. This may not seem like much, but it could mean the difference between being able to use 700 kbit/sec video or 714 kbit/sec, and every bit of quality counts.

In addition this gross inefficiency, AVI also has the following major limitations:

1. Only fixed-fps content can be stored. This is particularly limiting if the original material you want to encode is mixed content, for example a mix of NTSC video and film material. Actually there are hacks that can be used to store mixed-framerate content in AVI, but they increase the (already huge) overhead fivefold or more and so are not practical.

2. Audio in AVI files must be either constant-bitrate (CBR) or constant-framesize (i.e. all frames decode to the same number of samples). Unfortunately, the most efficient codec, Vorbis, does not meet either of these requirements. Therefore, if you plan to store your movie in AVI, you will have to use a less efficient codec such as MP3 or AC3.

Having said all that, MEncoder does not currently support variable-fps output or Vorbis encoding. Therefore, you may not see these as limitations if MEncoder is the only tool you will be using to produce your encodes. However, it is possible to use MEncoder only for video encoding, and then use external tools to encode audio and mux it into another container format.

#### 14.1.12.3. Muxing into the Matroska container

Matroska is a free, open standard container format, aiming to offer a lot of advanced features, which older containers like AVI cannot handle. For example, Matroska supports variable bitrate audio content (VBR), variable framerates (VFR), chapters, file attachments, error detection code (EDC) and modern A/V Codecs like "Advanced Audio Coding" (AAC), "Vorbis" or "MPEG-4 AVC" (H.264), next to nothing handled by AVI.

The tools required to create Matroska files are collectively called mkvtoolnix, and are available for most Unix platforms as well as Windows. Because Matroska is an open standard you may find other tools that suit you better, but since mkvtoolnix is the most common, and is supported by the Matroska team itself, we will only cover its usage.

Probably the easiest way to get started with Matroska is to use MMG, the graphical frontend shipped with mkvtoolnix, and follow the guide to mkvmerge GUI (mmg)

You may also mux audio and video files using the command line:

    mkvmerge -o output.mkv input_video.avi input_audio1.mp3 input_audio2.ac3

This would merge the video file `input_video.avi` and the two audio files `input_audio1.mp3` and `input_audio2.ac3` into the Matroska file `output.mkv`. Matroska, as mentioned earlier, is able to do much more than that, like multiple audio tracks (including fine-tuning of audio/video synchronization), chapters, subtitles, splitting, etc... Please refer to the documentation of those applications for more details.

[2] Be careful, however: Decoding DVD-resolution MPEG-4 AVC videos requires a fast machine (i.e. a Pentium 4 over 1.5GHz or a Pentium M over 1GHz).

[3] The same encode may not look the same on someone else's monitor or when played back by a different decoder, so future-proof your encodes by playing them back on different setups.

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