> Could we know how ffmpeg determine audio channel number from MP4 file? MP4 > container indicates it's channel count is 2, but ffprobe shows mono as > expected.
ffprobe probably looks at the actual AAC stream? Here's a hint: http://sourceforge.net/p/opencore-amr/mailman/message/31876733/ "The cause for this is that libavformat always writes 2 as number of channels in the m4a header regardless of the actual stream." (This was about HE-AAC, but may be valid here as well.) Is this causing any issues except your trust in the nature of the file? I must say I'm not sure whether that is actually true, whether it's okay for ffmpeg to do so, and whether this is still valid with recent ffmpeg. I can confirm the behavior though. Moritz P.S.: I like adding "other tools" to the confusion, without knowing what they look at: $ mediainfo audio_48k_mono.mp4 | grep -Fi chann Channel(s) : 2 channels Channel(s)_Original : 1 channel Channel positions : Front: C $ mplayer -vo null -ao null audio_48k_mono.mp4 2>/dev/null | grep -F AUDIO AUDIO: 44100 Hz, 1 ch, s16le, 48.3 kbit/6.85% (ratio: 6040->88200) $ # vlc says: Codec -> Stream 0 -> Channels: Stereo _______________________________________________ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-user
