Opened 8 years ago

#2086 new defect

Changing audio channels

Reported by: subjunk@… Owned by: reimar
Priority: normal Component: core
Version: HEAD Severity: normal
Keywords: Cc:
Blocked By: Blocking:
Reproduced by developer: Analyzed by developer:


A lot of videos these days with AC3 audio start with stereo (2.0) audio and then go to 5.1, because TV channels (like HBO) air the previews in 2.0 but the show in 5.1.
Most tools handle this (including FFmpeg) but MEncoder doesn't. The behaviour in MEncoder is this:
If you specify "-channels 2" or leave it blank, the audio is all output as stereo and there is no problem.
If you specify "-channels 6" the stereo part is output as stereo but the 5.1 part (the main part of the video) is slowed down by a lot (I'm guessing 3x).

MPlayer correctly switches from 2.0 to 5.1, it is only MEncoder that does not do it properly.

A sample video you can test is at

Command lines:

mencoder Sample-StereoToSurround?.mkv -oac lavc -of mpeg -ovc lavc -channels 6 -lavcopts vcodec=mpeg2video:acodec=ac3 -mc 0 -noskip -o output-with-channels.mpeg

mencoder Sample-StereoToSurround?.mkv -oac lavc -of mpeg -ovc lavc -lavcopts vcodec=mpeg2video:acodec=ac3 -mc 0 -noskip -o output-without-channels.mpeg

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