* Moritz Barsnick on Friday, December 05, 2014 at 10:37:14 +0100 >> 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
There's more confusion: https://trac.ffmpeg.org/ticket/4106 -- Auftreten Tarzan und Martha - ich hatte Sankt Pauli unterschätzt. _MICHAEL WEBER: MARTHA_ --->> http://www.blacktrash.org/baustellen/#martha _______________________________________________ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-user
