[FFmpeg-trac] #3783(ffmpeg:new): ffmpeg shoud init decoders before filters

[FFmpeg]

#3783: ffmpeg shoud init decoders before filters
--------------------------------------+--------------------------------
               Reporter:  Cigaes      |                  Owner:
                   Type:  defect      |                 Status:  new
               Priority:  minor       |              Component:  ffmpeg
                Version:  git-master  |               Keywords:
             Blocked By:              |               Blocking:
Reproduced by developer:  0           |  Analyzed by developer:  0
--------------------------------------+--------------------------------
 {{{
 ./ffmpeg_g -lavfi sine -t 5 -y /tmp/test.ac3
 ./ffmpeg_g -c ac3_fixed -i /tmp/test.ac3 -f null -
 }}}
 {{{
 ffmpeg version N-64757-g277e5ca Copyright (c) 2000-2014 the FFmpeg
 developers
   built on Jul 18 2014 10:43:46 with gcc 4.9 (Debian 4.9.0-7)
   configuration: --enable-shared --disable-static --enable-gpl --enable-
 libx264 --enable-libopus --enable-libass --enable-libfreetype --assert-
 level=2
   libavutil      52. 92.101 / 52. 92.101
   libavcodec     55. 69.100 / 55. 69.100
   libavformat    55. 48.101 / 55. 48.101
   libavdevice    55. 13.102 / 55. 13.102
   libavfilter     4. 11.102 /  4. 11.102
   libswscale      2.  6.100 /  2.  6.100
   libswresample   0. 19.100 /  0. 19.100
   libpostproc    52.  3.100 / 52.  3.100
 [ac3 @ 0xfc8cc0] Estimating duration from bitrate, this may be inaccurate
 Input #0, ac3, from '/tmp/test.ac3':
   Duration: 00:00:05.02, start: 0.000000, bitrate: 96 kb/s
     Stream #0:0: Audio: ac3, 44100 Hz, mono, fltp, 96 kb/s
 Output #0, null, to 'pipe:':
   Metadata:
     encoder         : Lavf55.48.101
     Stream #0:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
     Metadata:
       encoder         : Lavc55.69.100 pcm_s16le
 Stream mapping:
   Stream #0:0 -> #0:0 (ac3 (ac3_fixed) -> pcm_s16le (native))
 Press [q] to stop, [?] for help
 Input stream #0:0 frame changed from rate:44100 fmt:fltp ch:1 chl:mono to
 rate:44100 fmt:s16p ch:1 chl:mono
 size=N/A time=00:00:05.01 bitrate=N/A
 video:0kB audio:432kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: unknown
 }}}

 Notice this particular line:
 {{{
 Input stream #0:0 frame changed from rate:44100 fmt:fltp ch:1 chl:mono to
 rate:44100 fmt:s16p ch:1 chl:mono
 }}}

 This happens because filters are initialized before decoders: some
 properties of the stream, especially the sample format, often depend on
 the decoder. If a different decoder is used for decoding than the one used
 for probing, the result is considered a change in format. This is handled
 correctly but gives wrong information and wastes resources.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/3783>
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