DVD compliant mpeg2 on Linux

Either mjpegtools or the ffmpeg encoder can be used for creating the mpeg2 program streams needed for authoring DVDs on Linux. Our focus is encoding widescreen NTSC interlaced video source from a miniDV camcorder. We attempt to preserve as much of the quality of the original source as possible.

Needed Software

You need at least one on the following open source software projects to encode mpeg2 video on Linux.

An Encoding Script

I have written a script called encode-dvd that will create suitable mpeg2 files. Since other people's scripts are often difficult to use here are some explicit examples of encoding the file s001.avi using ffmpeg, mencoder and mjpegtools.

Ffmpeg

The ffmpeg encoder is faster on my computer than the mjpegtools tools encoder. However, if you want to use ffmpeg with interlaced video you may want to add the following patches. The first patch adds options that allow forcing the interlacing mode of an input file. The second patch adapts the 4:1:1 to 4:2:0 color space conversion used by ffmpeg so it works with interlaced video.

Apply these patches to ffmpeg-0.5. Then build it with

$ export LD_RUN_PATH=/usr/local/lib:/usr/lib:/lib
$ ./configure --prefix=/usr/local --enable-gpl --disable-debug \
    --enable-liba52 --enable-liba52bin --enable-libxvid \
    --enable-libx264 --enable-libfaac --enable-libfaad \
    --enable-libfaadbin --enable-libmp3lame --enable-libamr-nb \
    --enable-libamr-wb --enable-nonfree
$ make
$ su
% make install
% exit

It is important to specify LD_RUN_PATH so that the new version of ffmpeg links to the new versions of libavcodec, libavformat and libavutil.

A typical command using the patched version of ffmpeg-0.5 to encode a DVD compliant program stream from DV source is

$ ffmpeg -i s001.avi -interlace 1 -ildct -ilme -top 0 \
    -target dvd -aspect 16:9 \
    -qmin 5 -b 7000000 -ab 224000 -y s001.mpg

As of Aug 2009 the imgconvert.c.patch no longer applies to development versions of ffmpeg because the conv411() function has been removed. It appears that the development code still exhibits chroma subsampling errors with interlaced material. This is confirmed by Kevin Murraya in Believed Incorrect Chroma Subsampling on Interlaced 4:2:2 to 4:2:0. One can use y4mscaler to work around the chroma subsampling errors.

$ ffmpeg -i s001.avi -y s001.wav
$ ffmpeg -i s001.avi -f yuv4mpegpipe -pix_fmt yuv411p -y /dev/stdout |
  y4mscaler -I ilace=BOTTOM_FIRST -O chromass=420mpeg2 |
  ffmpeg -f yuv4mpegpipe -i /dev/stdin -i s001.wav \
    -interlace 1 -top 0 -flags +ildct+ilme \
    -target dvd -aspect 16:9 \
    -qmin 5 -b 7000000 -ab 224000 -y s001.mpg

There is also a change in syntax for specifying the ildct and ilme options in the development versions of ffmpeg.

Mencoder

I have not recently used mencoder to encode DVD compliant mpeg2 streams. Since mencoder uses the mpeg2 encoder from ffmpeg the results should be similar in quality to what is obtained from ffmpeg directly. Here is an untested command for mencoder that should do the same thing as the previous ffmpeg example.

$ mencoder s001.avi -aoc lavc -ovc lavc \
    -lavcopts acodec=ac3:abitrate=224:vcodec=mpeg2video:\
ildct:ilme:top=0:vbitrate=7000:vqmin=5:vrc_maxrate=7500:\
vrc_buf_size=1835:aspect=16/9 \
    -vf harddup,dsize=16/9 \
    -of mpeg -mpegopts format=dvd:tsaf:vaspect=16/9 \
    -o s001.mpg

I have not checked whether mencoder correctly subsamples the chroma when converting interlaced DV source to interlaced mpeg2 video.

Mjpegtools

The mjpegtools encoder runs more slowly than ffmpeg on my computer; however, no patches are needed to handle interlaced video. The encoding commands

$ lav2yuv s001.avi |
    yuvcorrect -T INTERLACED_BOTTOM_FIRST |
    mpeg2enc -M0 -nn -a3 -f8 -G18 -b7000 -V230 -q9 -o s001.m2v
$ lav2wav s001.avi > s001.wav
$ toolame -b224 -s48 s001.wav s001.m2a
$ mplex -f8 s001.m2v s001.m2a -o s001.mpg

work, but unfortunately reduce the effective color space to 4:1:0. Better results can be obtained by using y4mscaler and the commands

$ lav2yuv s001.avi -C 411 |
    y4mscaler -I ilace=BOTTOM_FIRST -O chromass=420mpeg2 |
    mpeg2enc -M0 -nn -a3 -f8 -G18 -b7000 -V230 -q9 -o s001.m2v
$ lav2wav s001.avi > s001.wav
$ toolame -b224 -s48 s001.wav s001.m2a
$ mplex -f8 s001.m2v s001.m2a -o s001.mpg

This interpolates the chroma in the horizontal direction before subsampling it vertically.

Conclusions

There are a number of ways to encode DVD complaint mpeg2 program streams on Linux. The commands are relatively straight forward. The script encode-dvd makes specifying quality, aspect ratio and interlacing easier than typing all the options in by hand.

Color space subsampling errors for interlaced video are present in unpatched versions of ffmpeg and possibly mencoder. Avisynth does color space conversion correctly as detailed in Sampling. Note that color space upsampling errors of a similar nature are present in some DVD players as described in The 4:2:0 Interlaced Chroma Problem. Unfortunately, the two chroma errors don't cancel each other out.

As a final note, if you will be authoring a DVD consisting of more than one file in dvdauthor, do not mix mpeg2 files produced with ffmpeg and mjpegtools in the same video title. Stick with one encoding method for the entire project. Otherwise, the end result will be a DVD with two separate audio tracks: an ac3 audio track and a mp2 audio track in which each track is partially blank. Anyone watching such a DVD would have to manually switch between audio tracks while they watched in order to hear the sound.

Page written and maintained by Eric Olson
Last Updated: Wed Jul 15 23:28:05 PDT 2009