MKV transcoded to MKV with copied attachments is unplayable if output is stdout

[bubbleguuum]

Summary of the bug:

A MKV that contains attachments (for example additional fonts for subs) that is transcoded to another MKV, copying the attachements, results in an unplayable file ([02189f60] mkv demux error: cannot find any cluster, damaged file ?) if the output specified to ffmpeg is stdout (-) instead of a regular file.

If the attachements streams are omitted in the transcoded output file, the file is playable in both cases.

So there seems to be a specific problem with transcoding to stdout and MKV attachments.

How to reproduce:

First, donwload this MKV containing attachments:
​http://www.auby.no/files/video_tests/h264_720p_hp_5.1_6mbps_ac3_unstyled_subs_planet.mkv

Let's transcode it to MKV, copying the attachement streams, to a regular file named file1.mkv. This file is playabale.

$ ffmpeg -async 1 -i h264_720p_hp_5.1_6mbps_ac3_unstyled_subs_planet.mkv -map 0 -vf scale="trunc(oh*a/2)*2:240" -vcodec libx264 -preset medium -acodec libmp3lame -ac 2 -ab 128000 -f matroska file1.mkv
ffmpeg version 1.2 Copyright (c) 2000-2013 the FFmpeg developers
  built on Mar 28 2013 00:28:48 with gcc 4.8.0 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-libass --enable-libbluray --enable-libcaca --enable-libfreetype --enable-libgsm --enable-libilbc --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --enable-zlib
  libavutil      52. 18.100 / 52. 18.100
  libavcodec     54. 92.100 / 54. 92.100
  libavformat    54. 63.104 / 54. 63.104
  libavdevice    54.  3.103 / 54.  3.103
  libavfilter     3. 42.103 /  3. 42.103
  libswscale      2.  2.100 /  2.  2.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  2.100 / 52.  2.100
Input #0, matroska,webm, from 'h264_720p_hp_5.1_6mbps_ac3_unstyled_subs_planet.mkv':
  Metadata:
    title           : Planet.Earth.EP01.From.Pole.to.Pole.2006.720p.HDDVD.x264-ESiR
    creation_time   : 2011-03-01 00:35:17
  Duration: 00:01:52.83, start: 0.000000, bitrate: 7066 kb/s
    Stream #0:0(eng): Video: h264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9, 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
    Metadata:
      title           : Planet Earth - EP01 - From Pole to Pole
    Stream #0:1(eng): Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s (default)
    Metadata:
      title           : AC3 5.1
    Stream #0:2(eng): Subtitle: ssa (default)
    Stream #0:3(rum): Subtitle: ssa
Codec 0x18000 is not in the full list.
    Stream #0:4: Attachment: unknown_codec
    Metadata:
      filename        : exprswy_free.ttf
      mimetype        : application/x-truetype-font
Codec 0x18000 is not in the full list.
    Stream #0:5: Attachment: unknown_codec
    Metadata:
      filename        : Framd.TTF
      mimetype        : application/x-truetype-font
-async is forwarded to lavfi similarly to -af aresample=async=1:min_hard_comp=0.100000:first_pts=0.
[libx264 @ 0422f380] using SAR=640/639
[libx264 @ 0422f380] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
[libx264 @ 0422f380] profile High, level 2.1
[libx264 @ 0422f380] 264 - core 130 r2274 c832fe9 - H.264/MPEG-4 AVC codec - Copyleft 2003-2013 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=12 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=23 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, matroska, to 'file1.mkv':
  Metadata:
    title           : Planet.Earth.EP01.From.Pole.to.Pole.2006.720p.HDDVD.x264-ESiR
    encoder         : Lavf54.63.104
    Stream #0:0(eng): Video: h264 (H264 / 0x34363248), yuv420p, 426x240 [SAR 640:639 DAR 16:9], q=-1--1, 1k tbn, 23.98 tbc (default)
    Metadata:
      title           : Planet Earth - EP01 - From Pole to Pole
    Stream #0:1(eng): Audio: mp3 (U[0][0][0] / 0x0055), 48000 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      title           : AC3 5.1
    Stream #0:2(eng): Subtitle: ssa (default)
    Stream #0:3(rum): Subtitle: ssa
Codec 0x18000 is not in the full list.
    Stream #0:4: Attachment: unknown_codec
    Metadata:
      filename        : exprswy_free.ttf
      mimetype        : application/x-truetype-font
Codec 0x18000 is not in the full list.
    Stream #0:5: Attachment: unknown_codec
    Metadata:
      filename        : Framd.TTF
      mimetype        : application/x-truetype-font
Stream mapping:
  Stream #0:0 -> #0:0 (h264 -> libx264)
  Stream #0:1 -> #0:1 (ac3 -> libmp3lame)
  Stream #0:2 -> #0:2 (ass -> ass)
  Stream #0:3 -> #0:3 (ass -> ass)
  Stream #0:4 -> #0:4 (copy)
  Stream #0:5 -> #0:5 (copy)
Press [q] to stop, [?] for help
frame= 2705 fps=155 q=2686567.0 Lsize=   11312kB time=00:01:52.84 bitrate= 821.2kbits/s
video:9298kB audio:1764kB subtitle:2 global headers:2kB muxing overhead 2.238986%
[libx264 @ 0422f380] frame I:20    Avg QP:19.09  size: 15456
[libx264 @ 0422f380] frame P:1418  Avg QP:23.83  size:  5843
[libx264 @ 0422f380] frame B:1267  Avg QP:25.03  size:   730
[libx264 @ 0422f380] consecutive B-frames: 29.4% 21.1% 10.3% 39.2%
[libx264 @ 0422f380] mb I  I16..4: 39.5% 30.6% 30.0%
[libx264 @ 0422f380] mb P  I16..4:  0.4%  0.4%  0.8%  P16..4: 26.9% 16.7% 13.4%  0.0%  0.0%    skip:41.4%
[libx264 @ 0422f380] mb B  I16..4:  0.0%  0.0%  0.0%  B16..8: 29.4%  2.7%  1.3%  direct: 3.2%  skip:63.4%  L0:32.1% L1:49.9% BI:18.0%
[libx264 @ 0422f380] 8x8 transform intra:27.2% inter:46.1%
[libx264 @ 0422f380] coded y,uvDC,uvAC intra: 64.7% 65.6% 50.9% inter: 23.3% 12.8% 1.7%
[libx264 @ 0422f380] i16 v,h,dc,p: 70% 10%  9% 11%
[libx264 @ 0422f380] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 11% 18% 19%  8%  8%  7%  8%  8% 13%
[libx264 @ 0422f380] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 10% 18% 15%  9%  9%  8% 10%  7% 13%
[libx264 @ 0422f380] i8c dc,h,v,p: 65% 18% 11%  6%
[libx264 @ 0422f380] Weighted P-Frames: Y:11.3% UV:0.9%
[libx264 @ 0422f380] ref P L0: 70.0% 20.6%  5.8%  3.4%  0.2%
[libx264 @ 0422f380] ref B L0: 87.3%  9.6%  3.1%
[libx264 @ 0422f380] ref B L1: 87.6% 12.4%
[libx264 @ 0422f380] kb/s:675.06

Now let's transcode it but specifying stdout (-) as the output and redirecting stdout to file2.mkv. file2.mkv is not playabale and VLC gives error "mkv demux error: cannot find any cluster, damaged file ?". Discarding the attachement streams in the resulting file would render the file playable.

$ ffmpeg -async 1 -i h264_720p_hp_5.1_6mbps_ac3_unstyled_subs_planet.mkv -map 0 -vf scale="trunc(oh*a/2)*2:240" -vcodec libx264 -preset medium -acodec libmp3lame -ac 2 -ab 128000 -f matroska - > file2.mkv
ffmpeg version 1.2 Copyright (c) 2000-2013 the FFmpeg developers
  built on Mar 28 2013 00:28:48 with gcc 4.8.0 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-libass --enable-libbluray --enable-libcaca --enable-libfreetype --enable-libgsm --enable-libilbc --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --enable-libxvid --enable-zlib
  libavutil      52. 18.100 / 52. 18.100
  libavcodec     54. 92.100 / 54. 92.100
  libavformat    54. 63.104 / 54. 63.104
  libavdevice    54.  3.103 / 54.  3.103
  libavfilter     3. 42.103 /  3. 42.103
  libswscale      2.  2.100 /  2.  2.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  2.100 / 52.  2.100
Input #0, matroska,webm, from 'h264_720p_hp_5.1_6mbps_ac3_unstyled_subs_planet.mkv':
  Metadata:
    title           : Planet.Earth.EP01.From.Pole.to.Pole.2006.720p.HDDVD.x264-ESiR
    creation_time   : 2011-03-01 00:35:17
  Duration: 00:01:52.83, start: 0.000000, bitrate: 7066 kb/s
    Stream #0:0(eng): Video: h264 (High), yuv420p, 1280x720, SAR 1:1 DAR 16:9, 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)
    Metadata:
      title           : Planet Earth - EP01 - From Pole to Pole
    Stream #0:1(eng): Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s (default)
    Metadata:
      title           : AC3 5.1
    Stream #0:2(eng): Subtitle: ssa (default)
    Stream #0:3(rum): Subtitle: ssa
Codec 0x18000 is not in the full list.
    Stream #0:4: Attachment: unknown_codec
    Metadata:
      filename        : exprswy_free.ttf
      mimetype        : application/x-truetype-font
Codec 0x18000 is not in the full list.
    Stream #0:5: Attachment: unknown_codec
    Metadata:
      filename        : Framd.TTF
      mimetype        : application/x-truetype-font
-async is forwarded to lavfi similarly to -af aresample=async=1:min_hard_comp=0.100000:first_pts=0.
[libx264 @ 0433cba0] using SAR=640/639
[libx264 @ 0433cba0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2
[libx264 @ 0433cba0] profile High, level 2.1
[libx264 @ 0433cba0] 264 - core 130 r2274 c832fe9 - H.264/MPEG-4 AVC codec - Copyleft 2003-2013 - http://www.videolan.org/x264.html - options: cabac=1 ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=-2 threads=12 lookahead_threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 keyint=250 keyint_min=23 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
Output #0, matroska, to 'pipe:':
  Metadata:
    title           : Planet.Earth.EP01.From.Pole.to.Pole.2006.720p.HDDVD.x264-ESiR
    encoder         : Lavf54.63.104
    Stream #0:0(eng): Video: h264 (H264 / 0x34363248), yuv420p, 426x240 [SAR 640:639 DAR 16:9], q=-1--1, 1k tbn, 23.98 tbc (default)
    Metadata:
      title           : Planet Earth - EP01 - From Pole to Pole
    Stream #0:1(eng): Audio: mp3 (U[0][0][0] / 0x0055), 48000 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      title           : AC3 5.1
    Stream #0:2(eng): Subtitle: ssa (default)
    Stream #0:3(rum): Subtitle: ssa
Codec 0x18000 is not in the full list.
    Stream #0:4: Attachment: unknown_codec
    Metadata:
      filename        : exprswy_free.ttf
      mimetype        : application/x-truetype-font
Codec 0x18000 is not in the full list.
    Stream #0:5: Attachment: unknown_codec
    Metadata:
      filename        : Framd.TTF
      mimetype        : application/x-truetype-font
Stream mapping:
  Stream #0:0 -> #0:0 (h264 -> libx264)
  Stream #0:1 -> #0:1 (ac3 -> libmp3lame)
  Stream #0:2 -> #0:2 (ass -> ass)
  Stream #0:3 -> #0:3 (ass -> ass)
  Stream #0:4 -> #0:4 (copy)
  Stream #0:5 -> #0:5 (copy)
Press [q] to stop, [?] for help
frame= 2705 fps=160 q=2686567.0 Lsize=   11316kB time=00:01:52.84 bitrate= 821.5kbits/s
video:9298kB audio:1764kB subtitle:2 global headers:2kB muxing overhead 2.277988%
[libx264 @ 0433cba0] frame I:20    Avg QP:19.09  size: 15456
[libx264 @ 0433cba0] frame P:1418  Avg QP:23.83  size:  5843
[libx264 @ 0433cba0] frame B:1267  Avg QP:25.03  size:   730
[libx264 @ 0433cba0] consecutive B-frames: 29.4% 21.1% 10.3% 39.2%
[libx264 @ 0433cba0] mb I  I16..4: 39.5% 30.6% 30.0%
[libx264 @ 0433cba0] mb P  I16..4:  0.4%  0.4%  0.8%  P16..4: 26.9% 16.7% 13.4%  0.0%  0.0%    skip:41.4%
[libx264 @ 0433cba0] mb B  I16..4:  0.0%  0.0%  0.0%  B16..8: 29.4%  2.7%  1.3%  direct: 3.2%  skip:63.4%  L0:32.1% L1:49.9% BI:18.0%
[libx264 @ 0433cba0] 8x8 transform intra:27.2% inter:46.1%
[libx264 @ 0433cba0] coded y,uvDC,uvAC intra: 64.7% 65.6% 50.9% inter: 23.3% 12.8% 1.7%
[libx264 @ 0433cba0] i16 v,h,dc,p: 70% 10%  9% 11%
[libx264 @ 0433cba0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 11% 18% 19%  8%  8%  7%  8%  8% 13%
[libx264 @ 0433cba0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 10% 18% 15%  9%  9%  8% 10%  7% 13%
[libx264 @ 0433cba0] i8c dc,h,v,p: 65% 18% 11%  6%
[libx264 @ 0433cba0] Weighted P-Frames: Y:11.3% UV:0.9%
[libx264 @ 0433cba0] ref P L0: 70.0% 20.6%  5.8%  3.4%  0.2%
[libx264 @ 0433cba0] ref B L0: 87.3%  9.6%  3.1%
[libx264 @ 0433cba0] ref B L1: 87.6% 12.4%
[libx264 @ 0433cba0] kb/s:675.06

[Hendrik]

Some MKV features may need seeking ability in the output file, so maybe those should then not be enabled if seeking is not available.

[Carl Eugen Hoyos]

Is this not reproducible with current git head?

[bubbleguuum]

Indeed, it is probably an issue related to stdout not being seekable. In any case, there is no error message.

It would be nice if attachments could be written in MKV without requiring seeking, if it is at all possible. That would allow to make such generated files http streamable on the fly without having to discard attachments.

[Carl Eugen Hoyos]

$ ffmpeg -i h264_720p_hp_5.1_6mbps_ac3_unstyled_subs_planet_cut.mkv -map 0 -f matroska - >out.mkv
ffmpeg version N-53670-g1a7ae6b Copyright (c) 2000-2013 the FFmpeg developers
  built on May 30 2013 13:02:45 with gcc 4.7 (SUSE Linux)
  configuration: --enable-gpl --disable-indev=jack
  libavutil      52. 34.100 / 52. 34.100
  libavcodec     55. 12.102 / 55. 12.102
  libavformat    55.  8.100 / 55.  8.100
  libavdevice    55.  2.100 / 55.  2.100
  libavfilter     3. 72.100 /  3. 72.100
  libswscale      2.  3.100 /  2.  3.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  3.100 / 52.  3.100
Input #0, matroska,webm, from 'h264_720p_hp_5.1_6mbps_ac3_unstyled_subs_planet_cut.mkv':
  Metadata:
    title           : Planet.Earth.EP01.From.Pole.to.Pole.2006.720p.HDDVD.x264-ESiR
    ENCODER         : Lavf55.8.100
  Duration: 00:00:30.04, start: 0.000000, bitrate: 448 kb/s
    Stream #0:0(eng): Video: mpeg4 (Simple Profile), yuv420p, 320x180 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 1k tbn, 13978 tbc (default)
    Metadata:
      title           : Planet Earth - EP01 - From Pole to Pole
      LANGUAGE        : eng
    Stream #0:1(eng): Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
    Metadata:
      title           : AC3 5.1
      LANGUAGE        : eng
    Stream #0:2(eng): Subtitle: ssa (default)
    Stream #0:3(rum): Subtitle: ssa
Codec 0x18000 is not in the full list.
    Stream #0:4: Attachment: unknown_codec
    Metadata:
      filename        : exprswy_free.ttf
      mimetype        : application/x-truetype-font
Codec 0x18000 is not in the full list.
    Stream #0:5: Attachment: unknown_codec
    Metadata:
      filename        : Framd.TTF
      mimetype        : application/x-truetype-font
Output #0, matroska, to 'pipe:':
  Metadata:
    title           : Planet.Earth.EP01.From.Pole.to.Pole.2006.720p.HDDVD.x264-ESiR
    encoder         : Lavf55.8.100
    Stream #0:0(eng): Video: mpeg4 (FMP4 / 0x34504D46), yuv420p, 320x180 [SAR 1:1 DAR 16:9], q=2-31, 200 kb/s, 1k tbn, 23.98 tbc (default)
    Metadata:
      title           : Planet Earth - EP01 - From Pole to Pole
      LANGUAGE        : eng
    Stream #0:1(eng): Audio: ac3 ([0] [0][0] / 0x2000), 48000 Hz, stereo, fltp, 192 kb/s (default)
    Metadata:
      title           : AC3 5.1
      LANGUAGE        : eng
    Stream #0:2(eng): Subtitle: ssa (default)
    Stream #0:3(rum): Subtitle: ssa
Codec 0x18000 is not in the full list.
    Stream #0:4: Attachment: unknown_codec
    Metadata:
      filename        : exprswy_free.ttf
      mimetype        : application/x-truetype-font
Codec 0x18000 is not in the full list.
    Stream #0:5: Attachment: unknown_codec
    Metadata:
      filename        : Framd.TTF
      mimetype        : application/x-truetype-font
Stream mapping:
  Stream #0:0 -> #0:0 (mpeg4 -> mpeg4)
  Stream #0:1 -> #0:1 (ac3 -> ac3)
  Stream #0:2 -> #0:2 (ssa -> ssa)
  Stream #0:3 -> #0:3 (ssa -> ssa)
  Stream #0:4 -> #0:4 (copy)
  Stream #0:5 -> #0:5 (copy)
Press [q] to stop, [?] for help
frame=  720 fps=0.0 q=2.0 Lsize=    1576kB time=00:00:30.03 bitrate= 430.0kbits/s
video:662kB audio:704kB subtitle:0 global headers:2kB muxing overhead 15.302800%

$ ffmpeg -i out.mkv
ffmpeg version N-53670-g1a7ae6b Copyright (c) 2000-2013 the FFmpeg developers
  built on May 30 2013 13:02:45 with gcc 4.7 (SUSE Linux)
  configuration: --enable-gpl --disable-indev=jack
  libavutil      52. 34.100 / 52. 34.100
  libavcodec     55. 12.102 / 55. 12.102
  libavformat    55.  8.100 / 55.  8.100
  libavdevice    55.  2.100 / 55.  2.100
  libavfilter     3. 72.100 /  3. 72.100
  libswscale      2.  3.100 /  2.  3.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  3.100 / 52.  3.100
[matroska,webm @ 0x276d020] Unknown entry 0x61A7
    Last message repeated 1 times
[matroska,webm @ 0x276d020] max_analyze_duration 5000000 reached at 5005008 microseconds
[matroska,webm @ 0x276d020] Estimating duration from bitrate, this may be inaccurate
Guessed Channel Layout for  Input Stream #0.5 : stereo
Input #0, matroska,webm, from 'out.mkv':
  Metadata:
    title           : Planet.Earth.EP01.From.Pole.to.Pole.2006.720p.HDDVD.x264-ESiR
    ENCODER         : Lavf55.8.100
  Duration: 00:01:07.25, start: 0.000000, bitrate: 191 kb/s
    Stream #0:0(eng): Video: mpeg4 (Simple Profile), yuv420p, 320x180 [SAR 1:1 DAR 16:9], 23.98 fps, 23.98 tbr, 1k tbn, 13978 tbc (default)
    Metadata:
      title           : Planet Earth - EP01 - From Pole to Pole
      LANGUAGE        : eng
    Stream #0:1(eng): Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
    Metadata:
      title           : AC3 5.1
      LANGUAGE        : eng
    Stream #0:2(eng): Subtitle: ssa (default)
    Stream #0:3(rum): Subtitle: ssa
    Stream #0:4(eng): Video: mpeg4, yuv420p, 320x180, SAR 1:1 DAR 16:9, 23.98 fps, 23.98 tbr, 1k tbn, 1k tbc (default)
    Metadata:
      title           : Planet Earth - EP01 - From Pole to Pole
      LANGUAGE        : eng
    Stream #0:5(eng): Audio: ac3, 48000 Hz, stereo, fltp (default)
    Metadata:
      title           : AC3 5.1
      LANGUAGE        : eng
    Stream #0:6(eng): Subtitle: ssa (default)
    Stream #0:7(rum): Subtitle: ssa
Codec 0x18000 is not in the full list.
    Stream #0:8: Attachment: unknown_codec
    Metadata:
      filename        : exprswy_free.ttf
      mimetype        : application/x-truetype-font
Codec 0x18000 is not in the full list.
    Stream #0:9: Attachment: unknown_codec
    Metadata:
      filename        : exprswy_free.ttf
      mimetype        : application/x-truetype-font
At least one output file must be specified

[mkver]

This has been fixed, most likely by commit 4687240d52b398573ae64447c82e3be24749224b. Since this commit, a dynamic buffer is used to write the attachments, so that seeking back to update the size elements is avoided in the non-seekable case.