[FFmpeg-user] aevalsrc stereo auto-converted to mono?

[Thierry Foucu]

Hi,

I was trying to use aevalsrc to create a stereo input, but it seems that
the code auto insert a aconvert filter to downmix my stereo input to mono.

Here is the output. Notice the aconvert filter being inserted and
converting my stereo to mono...
any option I should add to make sure the downmix does not happen?

Thanks.

$./ffmpeg -f lavfi -i aevalsrc="sin(440*2*PI*t):sin(880*2*PI*t)::d=10" -y
/tmp/test.ts
ffmpeg version N-37612-g94b1496 Copyright (c) 2000-2012 the FFmpeg
developers
  built on Feb  7 2012 09:54:52 with gcc 4.4.3
  configuration: --enable-gpl --enable-version3
  libavutil      51. 38.100 / 51. 38.100
  libavcodec     54.  1.100 / 54.  1.100
  libavformat    54.  0.100 / 54.  0.100
  libavdevice    53.  4.100 / 53.  4.100
  libavfilter     2. 62.100 /  2. 62.100
  libswscale      2.  1.100 /  2.  1.100
  libswresample   0.  6.100 /  0.  6.100
  libpostproc    52.  0.100 / 52.  0.100
[abuffersink @ 0x25d0040] auto-inserting filter 'auto-inserted aconvert 0'
between the filter 'Parsed_aevalsrc_0' and the filter 'out'
[aevalsrc @ 0x25cf060] sample_rate:44100 chlayout:stereo duration:10.000000
*[aconvert @ 0x25d6e60] fmt:dbl cl:stereo planar:1 -> fmt:s16 cl:mono
planar:0*
[lavfi @ 0x25ce3e0] Estimating duration from bitrate, this may be inaccurate
Input #0, lavfi, from 'aevalsrc=sin(440*2*PI*t):sin(880*2*PI*t)::d=10':
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
[mpegts @ 0x25d6840] muxrate VBR, pcr every 3 pkts, sdt every 200, pat/pmt
every 40 pkts
Output #0, mpegts, to '/tmp/test.ts':
  Metadata:
    encoder         : Lavf54.0.100
    Stream #0:0: Audio: mp2, 44100 Hz, mono, s16, 128 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le -> mp2)
Press [q] to stop, [?] for help
size=     181kB time=00:00:10.03 bitrate= 147.7kbits/s
video:0kB audio:157kB global headers:0kB muxing overhead 15.379823%