5.1 AAC Output Incorrectly Mapped

[Alan James]

I am trying to transcode an H.264 video with 5.1 DTS sound to an X264 video with 5.1 AAC sound. The output file's channels were not mapped correctly and the sound that should have been coming from the center speaker was coming out the right front speak. Both libfaac and the built in aac codec have given me the same problem.

I'm on Ubuntu 10.04 using the latest Git version of FFMPEG. Below is the bash script I used and FFPROBE output or the input file.

#!/bin/bash

ffmpeg -i 11.mov \
  -vcodec libx264 -b 1920k \
  -acodec aac -strict experimental -ab 192k \
  -vpre slow -threads 0 -map_metadata -1 -y 11_output.mp4
qt-faststart 11_output.mp4 11.mp4
rm 11_output.mp4

FFprobe version git-N-29011-g5381823, Copyright (c) 2007-2011 the FFmpeg developers
  built on Apr 10 2011 21:10:33 with gcc 4.4.3
  configuration: --enable-gpl --enable-version3 --enable-nonfree --enable-postproc --enable-libfaac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxvid --enable-x11grab
  libavutil    50. 40. 1 / 50. 40. 1
  libavcodec   52.117. 0 / 52.117. 0
  libavformat  52.106. 0 / 52.106. 0
  libavdevice  52.  4. 0 / 52.  4. 0
  libavfilter   1. 78. 0 /  1. 78. 0
  libswscale    0. 13. 0 /  0. 13. 0
  libpostproc  51.  2. 0 / 51.  2. 0
[matroska,webm @ 0x32cd050] Estimating duration from bitrate, this may be inaccurate
Input #0, matroska,webm, from '11.mkv':
  Duration: 00:01:04.39, start: 0.000000, bitrate: 1536 kb/s
    Stream #0.0(eng): Video: h264 (High), yuv420p, 1920x816 [PAR 1:1 DAR 40:17], 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc
    Metadata:
      title           : Tron.Legacy.2010.BluRay.1080p.x264.DTS-MySiLU
    Stream #0.1(eng): Audio: dca (DTS), 48000 Hz, 5.1, s16, 1536 kb/s (default)

[Carl Eugen Hoyos]

This is certainly reproducible.

Please note that the AAC encoder is marked experimental (and you found one of several problems).

[Carl Eugen Hoyos]

Please test this patch for the native encoder:
​http://thread.gmane.org/gmane.comp.video.ffmpeg.devel/132377

[Alan James]

That patch doesn't seem to work. I am still getting what should be the center speaker sound coming out of the right front speaker.

[Carl Eugen Hoyos]

How did you test? (Source file, command line, playback application)
I encoded wav files with ffmpeg -i source -ab 256k out.aac and played them back with QuickTime, it works fine for me for the following source channel layouts:
L - R - C
L - R - C - Cs
L - R - C - Ls - Rs
L - R - C - LFE - Ls - Rs

[Alan James]

I encoded a few different 5.1 files from different sources (Apple trailers, DVDs, etc) using the same script in my bug report. I played the file in VLC and in JW Player. I compiled the current Git version of FFMPEG, with this patch of course, on Kubuntu 11.04.

[Carl Eugen Hoyos]

Sample from ​http://www.cccp-project.net/beta/test_files/

ffmpeg -i ~/\[CCCP\]_Manhole_Test_Your_5.1_\[revamped\].mkv -acodec aac -strict experimental -qscale 5 -ab 192k out.mp4

With current, unpatched ffmpeg, the resulting file has broken channel order with vlc and QuickTime, after recompiling and re-encoding with the patch, channel order is fine with both applications.

Could you test again (or point me to a failing sample)?

[Alan James]

I crossed my fingers and I tested again using your script, your patch, the same file as you and I got a file with incorrectly mapped audio. The file is correctly mapped before processing and has the same errors listen above after.

[Alan James]

It's actually now working for me as well. I don't know what I was doing wrong before. Maybe I mis-copied something from your posted diff file. Thank you for all your help. This is working great now.

[Carl Eugen Hoyos]

New patches posted:
​http://thread.gmane.org/gmane.comp.video.ffmpeg.devel/132652

[Carl Eugen Hoyos]

Both patches applied.