[FFmpeg-user] Stereo AAC

[antony baxter]

Hi all,

I have some video files with a DTS audio stream. I'm trying to add a
couple of additional audio streams into the file, transcoded from the
DTS stream. My command line is:

   ffmpeg
      -i "${input}"
      -map 0:0
      -map 0:1
      -map 0:1
      -map 0:1
      -c:v copy
      -movflags +faststart
      -c:a:0 aac
      -b:a:0 192k
      -ac 2
      -metadata:s:a:0 title="AAC Stereo Audio"
      -c:a:1 ac3
      -ac 6
      -metadata:s:a:1 title="AC3 5.1 Audio"
      -c:a:2 copy
      -disposition:a -default
      -disposition:a:0 default
      -f mp4
      "${output}.mp4"

However, this isn't doing exactly what I expected. The output is:

Output #0, mp4, to 'output.mp4':
  Metadata:
    Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661),
yuv420p(progressive), 1920x1036 [SAR 1:1 DAR 480:259], q=2-31, 23.98
fps, 23.98 tbr, 16k tbn, 1k tbc (default)
    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz,
5.1, fltp, 192 kb/s (default)
    Metadata:
      title           : AAC Stereo Audio
    Stream #0:2(eng): Audio: ac3 (ac-3 / 0x332D6361), 48000 Hz, 5.1,
fltp, 448 kb/s
    Metadata:
      title           : AC3 5.1 Audio
    Stream #0:3(eng): Audio: dts (DTS) (mp4a / 0x6134706D), 48000 Hz,
5.1(side), fltp, 1536 kb/s

Note that Stream #0:1 is being output as AAC 5.1 instead of AAC stereo.

How come the -ac 2 flag is being ignored - do I need to specify which
stream this applies to, and if so how?

Thank you all

Ant.