[FFmpeg-trac] #6790(avfilter:new): Pan filter outputs silence when used without channel layout

[FFmpeg]

#6790: Pan filter outputs silence when used without channel layout
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             Reporter:  t.rapp    |                     Type:  defect
               Status:  new       |                 Priority:  normal
            Component:  avfilter  |                  Version:  git-master
             Keywords:            |               Blocked By:
             Blocking:            |  Reproduced by developer:  0
Analyzed by developer:  0         |
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 When using the pan filter with output channel-count only and unknown
 channel layout (like "1C") the filter output is silence in case the
 channel mixing instruction is not detected as "pure".

 How to reproduce using some "asynth" file generated from a FATE run:
 {{{
 % ./ffmpeg -i tests/data/asynth-44100-2.wav -f wav -filter:a
 "pan=1C|c0=c0+c1" -y ../temp/ffmpeg-pan-test01.wav -loglevel
 repeat+verbose
 ffmpeg version N-88290-gb629686 Copyright (c) 2000-2017 the FFmpeg
 developers
   built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.5) 20160609
   configuration: --enable-gpl --disable-network --enable-libsoxr --enable-
 libtwolame --enable-libmp3lame --enable-libvorbis --enable-libfreetype
 --enable-static --disable-shared --progs-suffix=-dbg --enable-debug
 --disable-optimizations --prefix=/usr/local
   libavutil      56.  0.100 / 56.  0.100
   libavcodec     58.  1.100 / 58.  1.100
   libavformat    58.  0.102 / 58.  0.102
   libavdevice    58.  0.100 / 58.  0.100
   libavfilter     7.  0.101 /  7.  0.101
   libswscale      5.  0.101 /  5.  0.101
   libswresample   3.  0.100 /  3.  0.100
   libpostproc    55.  0.100 / 55.  0.100
 [wav @ 0x42cb400] parser not found for codec pcm_s16le, packets or times
 may be invalid.
 Guessed Channel Layout for Input Stream #0.0 : stereo
 Input #0, wav, from 'tests/data/asynth-44100-2.wav':
   Duration: 00:00:06.00, bitrate: 1411 kb/s
     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz,
 stereo, s16, 1411 kb/s
 Stream mapping:
   Stream #0:0 -> #0:0 (pcm_s16le (native) -> pcm_s16le (native))
 Press [q] to stop, [?] for help
 [graph_0_in_0_0 @ 0x431b700] tb:1/44100 samplefmt:s16 samplerate:44100
 chlayout:0x3
 [Parsed_pan_0 @ 0x43134a0] o0 = 1 i0 + 1 i1
 Output #0, wav, to '../temp/ffmpeg-pan-test01.wav':
   Metadata:
     ISFT            : Lavf58.0.102
     Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, 1
 channels, s16, 705 kb/s
     Metadata:
       encoder         : Lavc58.1.100 pcm_s16le
 No more output streams to write to, finishing.
 size=     517kB time=00:00:06.00 bitrate= 705.7kbits/s speed= 849x
 video:0kB audio:517kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: 0.014739%
 Input file #0 (tests/data/asynth-44100-2.wav):
   Input stream #0:0 (audio): 259 packets read (1058400 bytes); 259 frames
 decoded (264600 samples);
   Total: 259 packets (1058400 bytes) demuxed
 Output file #0 (../temp/ffmpeg-pan-test01.wav):
   Output stream #0:0 (audio): 259 frames encoded (264600 samples); 259
 packets muxed (529200 bytes);
   Total: 259 packets (529200 bytes) muxed

 }}}

--
Ticket URL: <https://trac.ffmpeg.org/ticket/6790>
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