Enhancement: can only concat opus in opus container

[artofit]

Ffmpeg can only concat Opus files if they are in an opus container.

Test scenario:
Download a test file, for instance Inolvidable -Bachata 2013 by vk.comclub_sdm-.mp3 from ​http://mp3monkey.net/mp3/Migz.html

First execute:

ffmpeg -i "Migz-Inolvidable_-_Bachata_2013_by_vk_com_club_sdm_-.mp3" -ss 00:00:00 -t 00:01:00 -c:a libopus part1.mkv -ss 00:01:00 -c:a libopus part2.mkv

Now,

ffmpeg -i "concat:part1.mkv|part2.mkv" -c copy concat.mkv

Console output, see below.
Notice:
1/ it fails to perform the concat.
2/ if you replace ".mkv" by ".opus" it does work
3/ if you replace ".mkv" by ".webM" it also fails

I suspect other audio filters (​https://www.ffmpeg.org/ffmpeg-filters.html#Audio-Filters) or containers (mp4) will also fail.

F:\MM audio\test>ffmpeg -i "concat:part1.mkv|part2.mkv" -c copy concat.mkv
ffmpeg version N-63366-gf932e5f Copyright (c) 2000-2014 the FFmpeg developers
  built on May 21 2014 22:09:16 with gcc 4.8.2 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --
enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libcaca --enable-libfreetype --enab
le-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-libopencore-amrnb --enable-libop
encore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libsp
eex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvor
bis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid
 --enable-decklink --enable-zlib
  libavutil      52. 86.100 / 52. 86.100
  libavcodec     55. 63.100 / 55. 63.100
  libavformat    55. 40.100 / 55. 40.100
  libavdevice    55. 13.101 / 55. 13.101
  libavfilter     4.  5.100 /  4.  5.100
  libswscale      2.  6.100 /  2.  6.100
  libswresample   0. 19.100 /  0. 19.100
  libpostproc    52.  3.100 / 52.  3.100
[matroska,webm @ 0000000002ab8380] Could not find codec parameters for stream 0 (Video: h264, 520x398): unspecified pixel fo
rmat
Consider increasing the value for the 'analyzeduration' and 'probesize' options
Input #0, matroska,webm, from 'concat:part1.mkv|part2.mkv':
  Metadata:
    title           : Inolvidable -{Bachata 2013 by vk.com/club_sdm}-
    DATE            : 2013
    ALBUM           : Bachata by vk.com/club_sdm
    ARTIST          : Migz
    ALBUM_ARTIST    : http://vk.com/club_sdm
    COMPOSER        : http://vk.com/club_sdm
    COPYRIGHT       : http://vk.com/club_sdm
    ENCODED_BY      : http://vk.com/club_sdm
    GENRE           : Bachata
    TEXT            : - Social Dance Music -
                    : http://vk.com/club_sdm
                    : -------------------------------
                    : ?????? ?????? ??????? ??? ??? ??-?? ??????? ????????
                    : #?????? #?????? #??????? #??? #??? #??-?? #??????? #????????
                    : Salsa Bachata Kizomba Zouk Son Cha-cha Merengue Reggaeton
                    : #Salsa #Bachata #Kizomba #Zouk #Son #Cha-cha #Merengue #Reggaeton
                    : -------------------------------
                    : - Social Dance Music -
                    : http://vk.com/club_sdm
    PUBLISHER       : http://vk.com/club_sdm
    TIT3            : http://vk.com/club_sdm
    ENCODER         : Lavf55.40.100
  Duration: 00:01:00.01, start: 0.007000, bitrate: 421 kb/s
    Stream #0:0: Video: h264, 520x398, SAR 1:1 DAR 260:199, 30k fps, 1k tbr, 1k tbn, 2k tbc (default)
    Metadata:
      title           :
      COMMENT         : Cover (front)
      ENCODER         : Lavc55.63.100 libx264
    Stream #0:1: Audio: opus, 48000 Hz, stereo, fltp (default)
    Metadata:
      ENCODER         : Lavc55.63.100 libopus
Output #0, matroska, to 'concat.mkv':
  Metadata:
    title           : Inolvidable -{Bachata 2013 by vk.com/club_sdm}-
    DATE            : 2013
    ALBUM           : Bachata by vk.com/club_sdm
    ARTIST          : Migz
    ALBUM_ARTIST    : http://vk.com/club_sdm
    COMPOSER        : http://vk.com/club_sdm
    COPYRIGHT       : http://vk.com/club_sdm
    ENCODED_BY      : http://vk.com/club_sdm
    GENRE           : Bachata
    TEXT            : - Social Dance Music -
                    : http://vk.com/club_sdm
                    : -------------------------------
                    : ?????? ?????? ??????? ??? ??? ??-?? ??????? ????????
                    : #?????? #?????? #??????? #??? #??? #??-?? #??????? #????????
                    : Salsa Bachata Kizomba Zouk Son Cha-cha Merengue Reggaeton
                    : #Salsa #Bachata #Kizomba #Zouk #Son #Cha-cha #Merengue #Reggaeton
                    : -------------------------------
                    : - Social Dance Music -
                    : http://vk.com/club_sdm
    PUBLISHER       : http://vk.com/club_sdm
    TIT3            : http://vk.com/club_sdm
    encoder         : Lavf55.40.100
    Stream #0:0: Video: h264 (H264 / 0x34363248), 520x398 [SAR 1:1 DAR 260:199], q=2-31, 30k fps, 1k tbn, 1k tbc (default)
    Metadata:
      title           :
      COMMENT         : Cover (front)
      ENCODER         : Lavc55.63.100 libx264
    Stream #0:1: Audio: opus ([255][255][255][255] / 0xFFFFFFFF), 48000 Hz, stereo (default)
    Metadata:
      ENCODER         : Lavc55.63.100 libopus
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #0:1 -> #0:1 (copy)
Press [q] to stop, [?] for help
[matroska,webm @ 0000000002ab8380] Unknown entry 0x1A45DFA3
[matroska,webm @ 0000000002ab8380] Unknown entry 0x18538067
frame=    1 fps=0.0 q=-1.0 Lsize=     794kB time=00:01:05.55 bitrate=  99.3kbits/s
video:7kB audio:765kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 2.908109%

[Carl Eugen Hoyos]

The concat protocol cannot work for Matroska files.