7.8. Using MEncoder to create VCD/SVCD/DVD-compliant files
Indietro | Capitolo 7. La codifica con MEncoder | Avanti

## 7.8. Using MEncoder to create VCD/SVCD/DVD-compliant files

### 7.8.1. Format Constraints

MEncoder is capable of creating VCD, SCVD and DVD format MPEG files using the `libavcodec` library. These files can then be used in conjunction with vcdimager or dvdauthor to create discs that will play on a standard set-top player.

The DVD, SVCD, and VCD formats are subject to heavy constraints. Only a small selection of encoded picture sizes and aspect ratios are available. If your movie does not already meet these requirements, you may have to scale, crop or add black borders to the picture to make it compliant.

#### 7.8.1.1. Format Constraints

Format | Resolution | V. Codec | V. Bitrate | Sample Rate | A. Codec | A. Bitrate | FPS | Aspect
--- | --- | --- | --- | --- | --- | --- | --- | ---
NTSC DVD | 720x480, 704x480, 352x480, 352x240 | MPEG-2 | 9800 kbps | 48000 Hz | AC-3,PCM | 1536 kbps (max) | 30000/1001, 24000/1001 | 4:3, 16:9 (only for 720x480)
NTSC DVD | 352x240[a] | MPEG-1 | 1856 kbps | 48000 Hz | AC-3,PCM | 1536 kbps (max) | 30000/1001, 24000/1001 | 4:3, 16:9
NTSC SVCD | 480x480 | MPEG-2 | 2600 kbps | 44100 Hz | MP2 | 384 kbps (max) | 30000/1001 | 4:3
NTSC VCD | 352x240 | MPEG-1 | 1150 kbps | 44100 Hz | MP2 | 224 kbps | 24000/1001, 30000/1001 | 4:3
PAL DVD | 720x576, 704x576, 352x576, 352x288 | MPEG-2 | 9800 kbps | 48000 Hz | MP2,AC-3,PCM | 1536 kbps (max) | 25 | 4:3, 16:9 (only for 720x576)
PAL DVD | 352x288[a] | MPEG-1 | 1856 kbps | 48000 Hz | MP2,AC-3,PCM | 1536 kbps (max) | 25 | 4:3, 16:9
PAL SVCD | 480x576 | MPEG-2 | 2600 kbps | 44100 Hz | MP2 | 384 kbps (max) | 25 | 4:3
PAL VCD | 352x288 | MPEG-1 | 1152 kbps | 44100 Hz | MP2 | 224 kbps | 25 | 4:3
[a] These resolutions are rarely used for DVDs because they are fairly low quality.

If your movie has 2.35:1 aspect (most recent action movies), you will have to add black borders or crop the movie down to 16:9 to make a DVD or VCD. If you add black borders, try to align them at 16-pixel boundaries in order to minimize the impact on encoding performance. Thankfully DVD has sufficiently excessive bitrate that you do not have to worry too much about encoding efficiency, but SVCD and VCD are highly bitrate-starved and require effort to obtain acceptable quality.

#### 7.8.1.2. GOP Size Constraints

DVD, VCD, and SVCD also constrain you to relatively low GOP (Group of Pictures) sizes. For 30 fps material the largest allowed GOP size is 18. For 25 or 24 fps, the maximum is 15. The GOP size is set using the `keyint` option.

#### 7.8.1.3. Bitrate Constraints

VCD video is required to be CBR at 1152 kbps. This highly limiting constraint also comes along with an extremly low vbv buffer size of 327 kilobits. SVCD allows varying video bitrates up to 2500 kbps, and a somewhat less restrictive vbv buffer size of 917 kilobits is allowed. DVD video bitrates may range anywhere up to 9800 kbps (though typical bitrates are about half that), and the vbv buffer size is 1835 kilobits.

### 7.8.2. Output Options

MEncoder has options to control the output format. Using these options we can instruct it to create the correct type of file.

The options for VCD and SVCD are called xvcd and xsvcd, because they are extended formats. They are not strictly compliant, mainly because the output does not contain scan offsets. If you need to generate an SVCD image, you should pass the output file to vcdimager.

VCD:

    -of mpeg -mpegopts format=xvcd

SVCD:

    -of mpeg -mpegopts format=xsvcd

DVD (with timestamps on every frame, if possible):

    -of mpeg -mpegopts format=dvd:tsaf

DVD with NTSC Pullup:

    -of mpeg -mpegopts format=dvd:tsaf:telecine -ofps 24000/1001

This allows 24000/1001 fps progressive content to be encoded at 30000/1001 fps whilst maintaing DVD-compliance.

#### 7.8.2.1. Aspect Ratio

The aspect argument of `-lavcopts` is used to encode the aspect ratio of the file. During playback the aspect ratio is used to restore the video to the correct size.

16:9 or "Widescreen"

    -lavcopts aspect=16/9

4:3 or "Fullscreen"

    -lavcopts aspect=4/3

2.35:1 or "Cinemascope" NTSC

    -vf scale=720:368,expand=720:480 -lavcopts aspect=16/9

To calculate the correct scaling size, use the expanded NTSC width of 854/2.35 = 368

2.35:1 or "Cinemascope" PAL

    -vf scale=720:432,expand=720:576 -lavcopts aspect=16/9

To calculate the correct scaling size, use the expanded PAL width of 1024/2.35 = 432

#### 7.8.2.2. Maintaining A/V sync

In order to maintain audio/video synchronization throughout the encode, MEncoder has to drop or duplicate frames. This works rather well when muxing into an AVI file, but is almost guaranteed to fail to maintain A/V sync with other muxers such as MPEG. This is why it is necessary to append the `harddup` video filter at the end of the filter chain to avoid this kind of problem. You can find more technical information about `harddup` in the section Improving muxing and A/V sync reliability or in the manual page.

#### 7.8.2.3. Sample Rate Conversion

If the audio sample rate in the original file is not the same as required by the target format, sample rate conversion is required. This is achieved using the `-srate` option and the `-af lavcresample` audio filter together.

DVD:

    -srate 48000 -af lavcresample=48000

VCD and SVCD:

    -srate 44100 -af lavcresample=44100

### 7.8.3. Using libavcodec for VCD/SVCD/DVD Encoding

#### 7.8.3.1. Introduction

`libavcodec` can be used to create VCD/SVCD/DVD compliant video by using the appropriate options.

#### 7.8.3.2. lavcopts

This is a list of fields in `-lavcopts` that you may be required to change in order to make a complaint movie for VCD, SVCD, or DVD:

- acodec: `mp2` for VCD, SVCD, or PAL DVD; `ac3` is most commonly used for DVD. PCM audio may also be used for DVD, but this is mostly a big waste of space. Note that MP3 audio is not compliant for any of these formats, but players often have no problem playing it anyway.

- abitrate: 224 for VCD; up to 384 for SVCD; up to 1536 for DVD, but commonly used values range from 192 kbps for stereo to 384 kbps for 5.1 channel sound.

- vcodec: `mpeg1video` for VCD; `mpeg2video` for SVCD; `mpeg2video` is usually used for DVD but you may also use `mpeg1video` for CIF resolutions.

- keyint: Used to set the GOP size. 18 for 30fps material, or 15 for 25/24 fps material. Commercial producers seem to prefer keyframe intervals of 12. It is possible to make this much larger and still retain compatibility with most players. A `keyint` of 25 should never cause any problems.

- vrc_buf_size: 327 for VCD, 917 for SVCD, and 1835 for DVD.

- vrc_minrate: 1152, for VCD. May be left alone for SVCD and DVD.

- vrc_maxrate: 1152 for VCD; 2500 for SVCD; 9800 for DVD. For SVCD and DVD, you might wish to use lower values depending on your own personal preferences and requirements.

- vbitrate: 1152 for VCD; up to 2500 for SVCD; up to 9800 for DVD. For the latter two formats, vbitrate should be set based on personal preference. For instance, if you insist on fitting 20 or so hours on a DVD, you could use vbitrate=400. The resulting video quality would probably be quite bad. If you are trying to squeeze out the maximum possible quality on a DVD, use vbitrate=9800, but be warned that this could constrain you to less than an hour of video on a single-layer DVD.

- vstrict: `vstrict`=0 should be used to create DVDs. Without this option, MEncoder creates a stream that cannot be correctly decoded by some standalone DVD players.

#### 7.8.3.3. Examples

This is a typical minimum set of `-lavcopts` for encoding video:

VCD:

    -lavcopts vcodec=mpeg1video:vrc_buf_size=327:vrc_minrate=1152:\
    vrc_maxrate=1152:vbitrate=1152:keyint=15:acodec=mp2

SVCD:

    -lavcopts vcodec=mpeg2video:vrc_buf_size=917:vrc_maxrate=2500:vbitrate=1800:\
    keyint=15:acodec=mp2

DVD:

    -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:\
    keyint=15:vstrict=0:acodec=ac3

#### 7.8.3.4. Advanced Options

For higher quality encoding, you may also wish to add quality-enhancing options to lavcopts, such as `trell`, `mbd=2`, and others. Note that `qpel` and `v4mv`, while often useful with MPEG-4, are not usable with MPEG-1 or MPEG-2. Also, if you are trying to make a very high quality DVD encode, it may be useful to add `dc=10` to lavcopts. Doing so may help reduce the appearance of blocks in flat-colored areas. Putting it all together, this is an example of a set of lavcopts for a higher quality DVD:

    -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=8000:\
    keyint=15:trell:mbd=2:precmp=2:subcmp=2:cmp=2:dia=-10:predia=-10:cbp:mv0:\
    vqmin=1:lmin=1:dc=10:vstrict=0

### 7.8.4. Encoding Audio

VCD and SVCD support MPEG-1 layer II audio, using one of `toolame`, `twolame`, or `libavcodec`'s MP2 encoder. The libavcodec MP2 is far from being as good as the other two libraries, however it should always be available to use. VCD only supports constant bitrate audio (CBR) whereas SVCD supports variable bitrate (VBR), too. Be careful when using VBR because some bad standalone players might not support it too well.

For DVD audio, `libavcodec`'s AC-3 codec is used.

#### 7.8.4.1. toolame

For VCD and SVCD:

    -oac toolame -toolameopts br=224

#### 7.8.4.2. twolame

For VCD and SVCD:

    -oac twolame -twolameopts br=224

#### 7.8.4.3. libavcodec

For DVD with 2 channel sound:

    -oac lavc -lavcopts acodec=ac3:abitrate=192

For DVD with 5.1 channel sound:

    -channels 6 -oac lavc -lavcopts acodec=ac3:abitrate=384

For VCD and SVCD:

    -oac lavc -lavcopts acodec=mp2:abitrate=224

### 7.8.5. Putting it all Together

This section shows some complete commands for creating VCD/SVCD/DVD compliant videos.

#### 7.8.5.1. PAL DVD

    mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=dvd:tsaf \
      -vf scale=720:576,harddup -srate 48000 -af lavcresample=48000 \
      -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:\
    keyint=15:vstrict=0:acodec=ac3:abitrate=192:aspect=16/9 -ofps 25 \
      -o movie.mpg movie.avi

#### 7.8.5.2. NTSC DVD

    mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=dvd:tsaf \
      -vf scale=720:480,harddup -srate 48000 -af lavcresample=48000 \
      -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:\
    keyint=18:vstrict=0:acodec=ac3:abitrate=192:aspect=16/9 -ofps 30000/1001 \
      -o movie.mpg movie.avi

#### 7.8.5.3. PAL AVI Containing AC-3 Audio to DVD

If the source already has AC-3 audio, use -oac copy instead of re-encoding it.

    mencoder -oac copy -ovc lavc -of mpeg -mpegopts format=dvd:tsaf \
      -vf scale=720:576,harddup -ofps 25 \
      -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:\
    keyint=15:vstrict=0:aspect=16/9 -o movie.mpg movie.avi

#### 7.8.5.4. NTSC AVI Containing AC-3 Audio to DVD

If the source already has AC-3 audio, and is NTSC @ 24000/1001 fps:

    mencoder -oac copy -ovc lavc -of mpeg -mpegopts format=dvd:tsaf:telecine \
      -vf scale=720:480,harddup -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:\
      vrc_maxrate=9800:vbitrate=5000:keyint=15:vstrict=0:aspect=16/9 -ofps 24000/1001 \
      -o movie.mpg movie.avi

#### 7.8.5.5. PAL SVCD

    mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xsvcd -vf \
        scale=480:576,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
        vcodec=mpeg2video:mbd=2:keyint=15:vrc_buf_size=917:vrc_minrate=600:\
    vbitrate=2500:vrc_maxrate=2500:acodec=mp2:abitrate=224 -ofps 25 \
        -o movie.mpg movie.avi

#### 7.8.5.6. NTSC SVCD

    mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xsvcd  -vf \
        scale=480:480,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
        vcodec=mpeg2video:mbd=2:keyint=18:vrc_buf_size=917:vrc_minrate=600:\
    vbitrate=2500:vrc_maxrate=2500:acodec=mp2:abitrate=224 -ofps 30000/1001 \
        -o movie.mpg movie.avi

#### 7.8.5.7. PAL VCD

    mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xvcd -vf \
        scale=352:288,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
        vcodec=mpeg1video:keyint=15:vrc_buf_size=327:vrc_minrate=1152:\
    vbitrate=1152:vrc_maxrate=1152:acodec=mp2:abitrate=224 -ofps 25 \
        -o movie.mpg movie.avi

#### 7.8.5.8. NTSC VCD

    mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xvcd -vf \
        scale=352:240,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
        vcodec=mpeg1video:keyint=18:vrc_buf_size=327:vrc_minrate=1152:\
    vbitrate=1152:vrc_maxrate=1152:acodec=mp2:abitrate=224 -ofps 30000/1001 \
        -o movie.mpg movie.avi

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