[FFmpeg-user] Mapped clip contains unwanted 'ChannelPosition'

Richard David Williams richard.williams at llgc.org.uk
Mon May 19 11:17:10 CEST 2014

Hi Group

We are currently using ffmpeg to 'chop' IMX files(e.g multiple news clips) into individual clips, using the following ffmpeg -map command :-

>ffmpeg -i MultipleNewsClips.mov -ss 00:02:00.000 -scodec copy -map 0:6 -vcodec copy -map  0:1  -acodec copy -map 0:2 -map 0:3 -map 0:4 -map 0:5 -metadata creation_time="2014-05-01 12:00:00" -to 00:03:00.000 -y /tmp/clip_clip.mov -report
The input file contains a video track, 4 audio tracks and a timecode track and we are mapping all tracks to the output clip.

On running mediainfo v0.7.69 on the input file and the output clipped file, we are finding that FFmpeg is adding mediainfo field 'ChannelPositions' field in the output.( note does does exist in input file)

I contacted Sourceforge Mediainfo and they confirmed that FFmpeg injects this "chan" atom in every audio track:- 
In a nutshell, they explained :-
"this is a file not having any "chan" atom in the MOV header, FFmpeg injects this "chan"
atom in every audio track:

Channels (24 bytes)
Size: 24 (0x00000018)
Name: chan
Version: 0 (0x00)
Flags: 0 (0x000000)
ChannelLayoutTag: 6553601 (0x00640001)
ChannelBitmap: 0 (0x00000000)
NumberChannelDescriptions: 0 (0x00000000)

which is wrong (no ChannelLayoutTag input from the file, no
ChannelLayoutTag input for the command line, FFmpeg can not know about

ChannelLayoutTag real value)

Is there a way to prevent FFmpeg to inject "chan" atom or am I using the -map command incorrectly. ?
( note the all the other fields are spot on and as expected)

Many thanks

Richard Williams

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