I've got an .avi (1280x720 6 Channel 5.1 Audio 48,000 Hz 384 kb/s) that I'm trying to convert to an H264 M4V for streaming to my AppleTV and I'm using ffmpeg to do this.
ffmpeg -i input.avi -acodec copy -vcodec libx264 -vpre ultrafast -b 3331k -crf 22 -threads 0 output.m4v
I'm use the preset ultrafast just to test for the moment, but each time, the resulting m4v comes out with 2 channel audio, despite the fact that I've told ffmpeg to leave the audio alone.
And yeah, I know the AppleTV won't deal with the 384 kb/s.. if I attempt to convert the audio while the file is an AVI still I end up with audio sync issues (which is also bugging me).
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Strange. I've just run the same ffmpeg command on an .mpg file originating from a DVD, and the audio (AC-3) stays as 6 channels. I haven't got a 6 channel .avi file to try as a source.
How do you know that the .m4v file is only 2 channel? Can you open both files with mediainfo, and post the details here?
Also, what does ffmpeg output while the conversion is taking place? It should be something like this:
Output #0, ipod, to 'test_02.m4v': Metadata: encoder : Lavf52.93.0 Stream #0.0: Video: libx264, yuv420p, 720x576 [PAR 64:45 DAR 16:9], q=10-51, 3331 kb/s, 25 tbn, 25 tbc Stream #0.1: Audio: ac3, 48000 Hz, 5.1, 448 kb/s Stream mapping: Stream #0.0 -> #0.0 Stream #0.1 -> #0.1 Press [q] to stop encoding