request channel layout does not work with some DTS streams

[Michael Niedermayer]

Summary of the bug:
How to reproduce:

ffmpeg -request_channel_layout 3 -i vc1_dts_mplayerAudioProblem_sb41_cut.m2ts out.wav
vs.
ffmpeg-ref -request_channels 2 -i vc1_dts_mplayerAudioProblem_sb41_cut.m2ts out.wav

This is a regression from the users point of view as request_channels has been removed
sample file available here: ​http://samples.ffmpeg.org/ffmpeg-bugs/trac/ticket1827/vc1_dts_mplayerAudioProblem_sb41_cut.m2ts

[Carl Eugen Hoyos]

$ ffmpeg -request_channel_layout 3 -i vc1_dts_mplayerAudioProblem_sb41_cut.m2ts out.wav
ffmpeg version N-74956-g8d860f9 Copyright (c) 2000-2015 the FFmpeg developers
  built with gcc 4.3 (SUSE Linux)
  configuration: --enable-gpl
  libavutil      55.  0.100 / 55.  0.100
  libavcodec     57.  0.100 / 57.  0.100
  libavformat    57.  0.100 / 57.  0.100
  libavdevice    57.  0.100 / 57.  0.100
  libavfilter     6.  0.100 /  6.  0.100
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.100 /  2.  0.100
  libpostproc    54.  0.100 / 54.  0.100
[mpegts @ 0x9612280] Failed to open codec in av_find_stream_info
[mpegts @ 0x9612280] PES packet size mismatch
    Last message repeated 1 times
Input #0, mpegts, from 'vc1_dts_mplayerAudioProblem_sb41_cut.m2ts':
  Duration: 00:00:00.54, start: 867.477311, bitrate: 15521 kb/s
  Program 1
    Stream #0:0[0x1011]: Video: vc1 (Advanced) (VC-1 / 0x312D4356), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 90k tbn, 47.95 tbc
    Stream #0:1[0x1100](deu): Audio: dts (DTS-HD HRA) ([134][0][0][0] / 0x0086), 48000 Hz, 7.1, fltp
[dca @ 0x961a180] Channel layout '7.1' with 8 channels does not match specified number of channels 2: ignoring specified channel layout
Output #0, wav, to 'out.wav':
  Metadata:
    ISFT            : Lavf57.0.100
    Stream #0:0(deu): Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, 7.1, s16, 6144 kb/s
    Metadata:
      encoder         : Lavc57.0.100 pcm_s16le
Stream mapping:
  Stream #0:1 -> #0:0 (dts (dca) -> pcm_s16le (native))
Press [q] to stop, [?] for help
[dca @ 0x961a180] Number of channels changed in DCA decoder (2 -> 8)
[mpegts @ 0x9612280] PES packet size mismatch
[dca @ 0x961a180] Didn't get subframe DSYNC
[dca @ 0x961a180] Error decoding DTS-XXCH extension
    Last message repeated 1 times
size=     360kB time=00:00:00.48 bitrate=6145.7kbits/s
video:0kB audio:360kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.027669%

[Carl Eugen Hoyos]

For the given sample, this ticket was fixed in ae5b2c52