[FFmpeg-trac] #5718(avcodec:open): ffmpeg not remapping channels for libopus automatically

[FFmpeg]

#5718: ffmpeg not remapping channels for libopus automatically
-------------------------------------+-------------------------------------
             Reporter:  agressiv     |                    Owner:  (none)
                 Type:  defect       |                   Status:  open
             Priority:  important    |                Component:  avcodec
              Version:  git-master   |               Resolution:
             Keywords:  libopus      |               Blocked By:
  regression                         |
             Blocking:               |  Reproduced by developer:  1
Analyzed by developer:  0            |
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Comment (by everlanes):

 So I hacked together a quite complicated script to circumvent this issue
 (hopefully), but I am not very proud of it and I think it's strange I have
 to do it:

 {{{
 FILE="NameOfFileToConvert.mkv"

 read -r -d "" PYTHONCODE << EOD
 import sys, json

 data = json.load(sys.stdin)

 replace = {
         "5.0(side)": "5.0",
         "5.1(side)": "5.1",
         # you can add more mappings here
     }

 filter_string = "[:%d]channelmap=channel_layout='%s'"
 copy_string = "[:%d]anull"

 maps = [filter_string % (stream["index"],
 replace[stream["channel_layout"]])
         if stream.get("channel_layout") in replace.keys() else
         copy_string % (stream["index"])
         for stream in data["streams"]
         if stream["codec_type"] == "audio"]

 print(";".join(maps))
 EOD

 ffmpeg -i "$FILE" -map 0 \
     -c:v copy \
     -c:a libopus -filter_complex \
         `ffprobe -hide_banner -show_streams -print_format json "$FILE" | \
         python3 -c "$PYTHONCODE"` \
     -c:s copy \
     "$OUT_FILE"
 }}}

 So basically I get all streams of the original file and pipe it into a
 python script that creates the filter string that remaps all problematic
 streams. This string is then printed and used as an argument for the
 ffmpeg call...

 Does it work? Hopefully. Is it nice? Definitely not! There should be some
 kind of an (optionally) fallback mechanism in ffmpeg and/or libopus for
 unsupported channel layouts.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/5718#comment:21>
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