[FFmpeg-user] More on audio stream mapping
tim.nicholson at bbc.co.uk
Fri Dec 16 13:11:50 CET 2011
I have a file containing 1 video and 4 mono audio streams, and wish to
create a file with 1 video and 2 stereo audio streams.
Under the old API the extra audio stream was added after the output
filename, but now it is supposed to be done via the -map and
It therefore seems that the correct way to now achieve this is:-
ffmpeg -i archive.gxf -c:v copy \
-c:a libfaac -b:a 96k -ar 48k \
-map 0:0 -map 0:1 -map 0:2 \
-ac 2 -map_channel 0.1.0:0.1 -map_channel 0.2.0:0.1 \
-ac 2 -map_channel 0.3.0:0.2 -map_channel 0.4.0:0.2 \
From my reading of the documentation the:-
-map 0:0 -map 0:1 -map 0:2
maps the video and first two audio streams to the output file, which is
not the mapping I actually want but is the only way I can see to add the
extra output audio stream. Then the:-
commands overwrite this mapping to put the audio channels where I want them.
Adding streams by performing a mapping that is not wanted seems to me to
be counter intuitive. Or have I misunderstood things?
It also appears that you cannot use -c:a copy if using -map_channel as
the copy copies the stream as is, and not the channel.
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