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  • CRF/CQP is incompatible with 2pass. FFmpeg error

    22 juillet 2020, par user12129980

    This is my command :

    



    ..\ffmpeg -y -i "D:\FFMPEG\ffmpeg-20200129-de1b2aa-win64-static\bin\test\aa_start_with_BAGAN.mp4" -c:v libx264 -preset ultrafast -maxrate 3000k -bufsize 6000k -g 50 -c:a aac -b:a 128k -ac 2 -ar 44100 -an -pass 1 -f mp4 NUL   && ..\ffmpeg -i "D:\FFMPEG\ffmpeg-20200129-de1b2aa-win64-static\bin\test\aa_start_with_BAGAN.mp4" -c:v libx264 -s 1280x720 -preset ultrafast -maxrate 500k -bufsize 1000k -vf "scale=1280:-1,format=yuv420p" -g 50 -c:a aac -b:a 128k -ac 2 -ar 44100 -an -pass 2 aa_start_with_BAGAN.mp4_ultrafast_500.mp4


    



    in the output I get CRF/CQP is incompatible with 2pass, but I didnt use the cfr/-q option in the command at all, why do I get this error ?
Add the full metadata of FFMpeg maybe someone can help me with this ?
(-g 50 because the default fps is 25 base on the documentation)

    



    `ffmpeg version git-2020-01-29-de1b2aa Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 9.2.1 (GCC) 20200122
  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx --enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf
  libavutil      56. 38.100 / 56. 38.100
  libavcodec     58. 67.100 / 58. 67.100
  libavformat    58. 36.100 / 58. 36.100
  libavdevice    58.  9.103 / 58.  9.103
  libavfilter     7. 71.100 /  7. 71.100
  libswscale      5.  6.100 /  5.  6.100
  libswresample   3.  6.100 /  3.  6.100
  libpostproc    55.  6.100 / 55.  6.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'D:\FFMPEG\ffmpeg-20200129-de1b2aa-win64-static\bin\test\aa_start_with_BAGAN.mp4':
  Metadata:
    major_brand     : M4V
    minor_version   : 1
    compatible_brands: M4V mp42isom
    creation_time   : 2018-04-24T18:21:09.000000Z
  Duration: 00:35:54.00, start: 0.000000, bitrate: 1057 kb/s
    Stream #0:0(eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p(tv), 640x480 [SAR 1:1 DAR 4:3], 929 kb/s, 25 fps, 25 tbr, 50k tbn, 50 tbc (default)
    Metadata:
      creation_time   : 2018-04-24T18:21:09.000000Z
      handler_name    : Mainconcept MP4 Video Media Handler
      encoder         : AVC Coding
    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
    Metadata:
      creation_time   : 2018-04-24T18:21:09.000000Z
      handler_name    : Mainconcept MP4 Sound Media Handler
Codec AVOption b (set bitrate (in bits/s)) specified for output file #0 (NUL) has not been used for any stream. The most likely reason is either wrong type (e.g. a video option with no video streams) or that it is a private option of some encoder which was not actually used for any stream.
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[libx264 @ 0000024ec2de0f80] using SAR=1/1
[libx264 @ 0000024ec2de0f80] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0000024ec2de0f80] profile Constrained Baseline, level 3.0, 4:2:0, 8-bit
[libx264 @ 0000024ec2de0f80] 264 - core 159 - H.264/MPEG-4 AVC codec - Copyleft 2003-2019 - http://www.videolan.org/x264.html - options: cabac=0 ref=1 deblock=0:0:0 analyse=0:0 me=dia subme=0 psy=1 psy_rd=1.00:0.00 mixed_ref=0 me_range=16 chroma_me=1 trellis=0 8x8dct=0 cqm=0 deadzone=21,11 fast_pskip=1 chroma_qp_offset=0 threads=12 lookahead_threads=2 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=0 weightp=0 keyint=50 keyint_min=5 scenecut=0 intra_refresh=0 rc_lookahead=0 rc=crf mbtree=0 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 vbv_maxrate=3000 vbv_bufsize=6000 crf_max=0.0 nal_hrd=none filler=0 ip_ratio=1.40 aq=0
Output #0, mp4, to 'NUL':
  Metadata:
    major_brand     : M4V
    minor_version   : 1
    compatible_brands: M4V mp42isom
    encoder         : Lavf58.36.100
    Stream #0:0(eng): Video: h264 (libx264) (avc1 / 0x31637661), yuv420p, 640x480 [SAR 1:1 DAR 4:3], q=-1--1, 25 fps, 12800 tbn, 25 tbc (default)
    Metadata:
      creation_time   : 2018-04-24T18:21:09.000000Z
      handler_name    : Mainconcept MP4 Video Media Handler
      encoder         : Lavc58.67.100 libx264
    Side data:
      cpb: bitrate max/min/avg: 3000000/0/0 buffer size: 6000000 vbv_delay: N/A
frame=53849 fps=999 q=-1.0 Lsize=  496489kB time=00:35:53.92 bitrate=1888.3kbits/s speed=39.9x
video:496266kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.044919%
[libx264 @ 0000024ec2de0f80] frame I:1077  Avg QP:20.39  size: 38800
[libx264 @ 0000024ec2de0f80] frame P:52772 Avg QP:23.39  size:  8838
[libx264 @ 0000024ec2de0f80] mb I  I16..4: 100.0%  0.0%  0.0%
[libx264 @ 0000024ec2de0f80] mb P  I16..4:  8.4%  0.0%  0.0%  P16..4: 51.8%  0.0%  0.0%  0.0%  0.0%    skip:39.8%
[libx264 @ 0000024ec2de0f80] coded y,uvDC,uvAC intra: 44.8% 54.5% 18.3% inter: 30.2% 22.0% 2.0%
[libx264 @ 0000024ec2de0f80] i16 v,h,dc,p: 39% 25% 16% 19%
[libx264 @ 0000024ec2de0f80] i8c dc,h,v,p: 35% 23% 24% 17%
[libx264 @ 0000024ec2de0f80] kb/s:1887.41
ffmpeg version git-2020-01-29-de1b2aa Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 9.2.1 (GCC) 20200122
  configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass --enable-libdav1d --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp --enable-libvidstab --enable-libvorbis --enable-libvo-amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-libaom --enable-libmfx --enable-ffnvcodec --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf
  libavutil      56. 38.100 / 56. 38.100
  libavcodec     58. 67.100 / 58. 67.100
  libavformat    58. 36.100 / 58. 36.100
  libavdevice    58.  9.103 / 58.  9.103
  libavfilter     7. 71.100 /  7. 71.100
  libswscale      5.  6.100 /  5.  6.100
  libswresample   3.  6.100 /  3.  6.100
  libpostproc    55.  6.100 / 55.  6.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'D:\FFMPEG\ffmpeg-20200129-de1b2aa-win64-static\bin\test\aa_start_with_BAGAN.mp4':
  Metadata:
    major_brand     : M4V
    minor_version   : 1
    compatible_brands: M4V mp42isom
    creation_time   : 2018-04-24T18:21:09.000000Z
  Duration: 00:35:54.00, start: 0.000000, bitrate: 1057 kb/s
    Stream #0:0(eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p(tv), 640x480 [SAR 1:1 DAR 4:3], 929 kb/s, 25 fps, 25 tbr, 50k tbn, 50 tbc (default)
    Metadata:
      creation_time   : 2018-04-24T18:21:09.000000Z
      handler_name    : Mainconcept MP4 Video Media Handler
      encoder         : AVC Coding
    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
    Metadata:
      creation_time   : 2018-04-24T18:21:09.000000Z
      handler_name    : Mainconcept MP4 Sound Media Handler
Codec AVOption b (set bitrate (in bits/s)) specified for output file #0 (aa_start_with_BAGAN.mp4_ultrafast_500.mp4) has not been used for any stream. The most likely reason is either wrong type (e.g. a video option with no video streams) or that it is a private option of some encoder which was not actually used for any stream.
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
Press [q] to stop, [?] for help
[libx264 @ 0000013691fbda00] using SAR=3/4
[libx264 @ 0000013691fbda00] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX FMA3 BMI2 AVX2
[libx264 @ 0000013691fbda00] CRF/CQP is incompatible with 2pass.
Error initializing output stream 0:0 -- Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height
Conversion failed!`


    


  • Rails FFMPEG - convert to webm gives error for encoder 'libvpx-vp9'

    7 mai 2019, par Milind

    I am testing video conversion to convert video file into mp4 and webm.
    I have also setup ffmpeg and compiled properly.Mp4 conversion succeeds but webm breaks always complaining as -

    The encoder 'libvpx-vp9' is experimental but experimental codecs are not enabled, add '-strict -2' if you want to use it.

    its strange as I aready have vp8 present -

    mike1011:~/workspace (s1) $ ffmpeg -encoders | grep -i vp
    ffmpeg version git-2016-03-29-bf1495d Copyright (c) 2000-2016 the FFmpeg developers
     built with gcc 4.8 (Ubuntu 4.8.4-2ubuntu1~14.04.1)
     configuration: --enable-gpl --enable-libfaac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-librtmp --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-nonfree --enable-version3
     libavutil      55. 19.100 / 55. 19.100
     libavcodec     57. 32.100 / 57. 32.100
     libavformat    57. 29.101 / 57. 29.101
     libavdevice    57.  0.101 / 57.  0.101
     libavfilter     6. 40.102 /  6. 40.102
     libswscale      4.  0.100 /  4.  0.100
     libswresample   2.  0.101 /  2.  0.101
     libpostproc    54.  0.100 / 54.  0.100
    V..... libvpx               libvpx VP8 (codec vp8)
    V..X.. libvpx-vp9           libvpx VP9 (codec vp9)
    V..... wrapped_avframe      AVFrame to AVPacket passthrough
    A..... wavpack              WavPack

    my model..video.rb looks like -

    has_attached_file :video,
      :styles => {
         :mp4video => { :geometry => '1280x720>', :format => 'mp4',
           :convert_options => { :output => { :vcodec => 'libx264', :movflags => '+faststart',  :strict => :experimental} } },
         :webmvideo => { :geometry => '1280x720>', :format => 'webm',
           :convert_options => { :output => { :vcodec => 'libvpx-vp9'} } },
         :oggvideo => { :geometry => '1280x720>', :format => 'ogg',
           :convert_options => { :output => { :vcodec => 'libtheora',
             :acodec => 'libvorbis',  :strict => :experimental } } },
         screenshot: { geometry: '640x480#',  :convert_options => {
           :output => { :vframes => 1, :s => '300x169', :ss => '00:00:02'} } }
       },    
       :processors => [:transcoder],
        ###other setting comes here

     ##using delayed-paperclip for background processing of videos
     process_in_background :video

     def process_delayed!
       unless self.video.job_is_processing
         self.video.job_is_processing = true
         self.video.post_processing = true
         self.video.reprocess!
         self.video.job_is_processing = false
       end  
     end  

    I am sharing my complete output below(with error highlighted :)) -

       2.4.1 :003 > v=Video.find 25
         Video Load (1.8ms)  SELECT  "videos".* FROM "videos" WHERE "videos"."id" = $1 LIMIT 1  [["id", 25]]
        => #<video></video>mp4", video_file_size: 1105773, video_updated_at: "2019-02-02 00:17:37", duration: 18.112, slug: "sample320-mp4-dbb96526-5db1-4c59-9152-615fc077eca7", active: true, created_at: "2019-02-02 00:17:37", updated_at: "2019-02-02 00:17:37", video_processing: true>
       2.4.1 :004 > v.process_delayed!
       [paperclip] copying /videos/25/original/Sample320.mp4 to local file /tmp/6b5665997c56c12544e7069276f6660b20190203-677953-1jsw8d1.mp4
       [paperclip] Trying to link /tmp/6b5665997c56c12544e7069276f6660b20190203-677953-1jsw8d1.mp4 to /tmp/6b5665997c56c12544e7069276f6660b20190203-677953-1qmn2uk.mp4
       I, [2019-02-03T00:12:09.849885 #677953]  INFO -- : Running transcoding...
       ["/usr/local/bin/ffmpeg", "-y", "-i", "/tmp/6b5665997c56c12544e7069276f6660b20190203-677953-1jsw8d1.mp4", "-s", "360x240", "-aspect", "1.5", "/tmp/2f51a6ecbce019dcad28a46b5be980ec20190203-677953-rh2lh0.mp4"]

       I, [2019-02-03T00:12:16.060391 #677953]  INFO -- : Transcoding of /tmp/6b5665997c56c12544e7069276f6660b20190203-677953-1jsw8d1.mp4 to /tmp/2f51a6ecbce019dcad28a46b5be980ec20190203-677953-rh2lh0.mp4 succeeded

       [paperclip] Trying to link /tmp/2f51a6ecbce019dcad28a46b5be980ec20190203-677953-rh2lh0.mp4 to /tmp/2961027361de4afbbb86f7764a034ee020190203-677953-1g0vvwe.mp4
       I, [2019-02-03T00:12:16.082499 #677953]  INFO -- : Running transcoding...
       ["/usr/local/bin/ffmpeg", "-y", "-i", "/tmp/6b5665997c56c12544e7069276f6660b20190203-677953-1jsw8d1.mp4", "-s", "360x240", "-aspect", "1.5", "/tmp/2f51a6ecbce019dcad28a46b5be980ec20190203-677953-fv3pzs.webm"]

       E, [2019-02-03T00:12:16.202420 #677953] ERROR -- : Failed encoding...
       ["/usr/local/bin/ffmpeg", "-y", "-i", "/tmp/6b5665997c56c12544e7069276f6660b20190203-677953-1jsw8d1.mp4", "-s", "360x240", "-aspect", "1.5", "/tmp/2f51a6ecbce019dcad28a46b5be980ec20190203-677953-fv3pzs.webm"]

       ffmpeg version git-2016-03-29-bf1495d Copyright (c) 2000-2016 the FFmpeg developers
         built with gcc 4.8 (Ubuntu 4.8.4-2ubuntu1~14.04.1)
         configuration: --enable-gpl --enable-libfaac --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-librtmp --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-nonfree --enable-version3
         libavutil      55. 19.100 / 55. 19.100
         libavcodec     57. 32.100 / 57. 32.100
         libavformat    57. 29.101 / 57. 29.101
         libavdevice    57.  0.101 / 57.  0.101
         libavfilter     6. 40.102 /  6. 40.102
         libswscale      4.  0.100 /  4.  0.100
         libswresample   2.  0.101 /  2.  0.101
         libpostproc    54.  0.100 / 54.  0.100
       Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/tmp/6b5665997c56c12544e7069276f6660b20190203-677953-1jsw8d1.mp4':
         Metadata:
           major_brand     : isom
           minor_version   : 512
           compatible_brands: isomiso2avc1mp41
           encoder         : Lavf57.76.100
         Duration: 00:00:18.11, start: 0.000000, bitrate: 488 kb/s
           Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 360x240 [SAR 32:27 DAR 16:9], 353 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
           Metadata:
             handler_name    : VideoHandler
           Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 129 kb/s (default)
           Metadata:
             handler_name    : SoundHandler

    XXXXXXXXXXXXXXXXXXXXXXXX====== HERE COMES THE ERROR========XXXXXXXXXXXX
       [libvpx-vp9 @ 0x3e3dec0] The encoder 'libvpx-vp9' is experimental but experimental codecs are not enabled, add '-strict -2' if you want to use it.

       Errors: encoded file is invalid.

       Paperclip::Error: There was an error processing the transcoder for 6b5665997c56c12544e7069276f6660b20190203-677953-1jsw8d1
              ...
  • The ffmpeg webm_dash_manifest demuxer fails with webvtt subtitles

    30 janvier 2020, par Hyldrean

    I am trying to create a DASH manifest using ffmpeg and I encounter some difficulties with the subtitles. I get the error

    [webm_dash_manifest @ 0x55e19db48180] EBML header parsing failed
    [webm_dash_manifest @ 0x55e19db48180] Failed to read file headers
    subtitles.vtt: Operation not permitted

    The subtitles are encoded in the plain text webvtt format. I first assume that the EBML header are missing because the subtitles were not contained in a webm container. I then tried to create a webm file containing only the subtitles. It appears impossible.

    I think the problem comes from the webm_dash_manifest demuxer. It seeks metadata in a file with no metadata. However neither Google nor Stack Overflow give me an answer.

    The command I used :

    ffmpeg \
    -f webm_dash_manifest -i video.webm \
    -f webm_dash_manifest -i audio.webm \
    -f webm_dash_manifest -i subtitles.vtt \
    -map 0 -map 1 -map 2 \
    -c copy \
    -f webm_dash_manifest \
    -adaptation_sets "id=0,streams=0 id=1,streams=1 id=2,stream=2" \
    minimal.mpd

    and the ffmpeg output :

    ffmpeg version 3.2.14-1~deb9u1 Copyright (c) 2000-2019 the FFmpeg developers
     built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
     configuration: --prefix=/usr --extra-version='1~deb9u1' --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libebur128 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
     libavutil      55. 34.101 / 55. 34.101
     libavcodec     57. 64.101 / 57. 64.101
     libavformat    57. 56.101 / 57. 56.101
     libavdevice    57.  1.100 / 57.  1.100
     libavfilter     6. 65.100 /  6. 65.100
     libavresample   3.  1.  0 /  3.  1.  0
     libswscale      4.  2.100 /  4.  2.100
     libswresample   2.  3.100 /  2.  3.100
     libpostproc    54.  1.100 / 54.  1.100
    [webm_dash_manifest @ 0x55e19db17160] Could not find codec parameters for stream 0 (Video: vp9, none, 1280x534): unspecified pixel format
    Consider increasing the value for the 'analyzeduration' and 'probesize' options
    Input #0, webm_dash_manifest, from 'video.webm':
     Metadata:
       title           : Cloud Atlas
       ENCODER         : Lavf58.35.104
     Duration: 00:05:00.01, bitrate: 998 kb/s
       Chapter #0:0: start 0.000000, end 300.000000
       Metadata:
         title           : Chapter 01
       Stream #0:0(eng): Video: vp9, none, 1280x534, SAR 1:1 DAR 640:267, 23.98 fps, 23.98 tbr, 1k tbn, 1k tbc (default) (forced)
       Metadata:
         title           : Video @ 6.9 Mbps [frame B:188517 Avg QP:20.66]
         ENCODER         : Lavc58.66.100 libvpx-vp9
         DURATION        : 00:05:00.008000000
         webm_dash_manifest_duration: 300008
         webm_dash_manifest_initialization_range: 900
         webm_dash_manifest_file_name: video.webm
         webm_dash_manifest_track_number: 1
         webm_dash_manifest_cues_start: 37455991
         webm_dash_manifest_cues_end: 37457486
         webm_dash_manifest_bandwidth: 1420427
         webm_dash_manifest_cluster_keyframe: 1
         webm_dash_manifest_cue_timestamps: 298715
    Input #1, webm_dash_manifest, from 'audio.webm':
     Metadata:
       title           : Cloud Atlas
       ENCODER         : Lavf58.35.104
     Duration: 00:05:00.01, bitrate: 126 kb/s
       Chapter #1:0: start 0.000000, end 300.000000
       Metadata:
         title           : Chapter 01
       Stream #1:0(eng): Audio: opus, 48000 Hz, stereo, fltp (default)
       Metadata:
         title           : Audio Eng DTS 5.1 channels 24 bits @ 1509 Kbps cbr
         ENCODER         : Lavc58.66.100 libopus
         DURATION        : 00:05:00.007000000
         webm_dash_manifest_duration: 300007
         webm_dash_manifest_initialization_range: 838
         webm_dash_manifest_file_name: audio.webm
         webm_dash_manifest_track_number: 1
         webm_dash_manifest_cues_start: 4744091
         webm_dash_manifest_cues_end: 4745279
         webm_dash_manifest_bandwidth: 137531
         webm_dash_manifest_cluster_keyframe: 1
         webm_dash_manifest_cue_timestamps: 295000
    [webm_dash_manifest @ 0x55e19db48180] EBML header parsing failed
    [webm_dash_manifest @ 0x55e19db48180] Failed to read file headers
    subtitles.vtt: Operation not permitted

    I noticed that ffmpeg -f webm_dash_manifest -i subtitles.vtt suffices to reproduce the error.

    I have also tried without the -f webm_dash_manifest flag, with no success :

    ffmpeg \
    -f webm_dash_manifest -i video.webm \
    -f webm_dash_manifest -i audio.webm \
    -i subtitles.vtt \
    -map 0 -map 1 -map 2 \
    -c copy \
    -f webm_dash_manifest \
    -adaptation_sets "id=0,streams=0 id=1,streams=1 id=2,stream=2" minimal.mpd

    Output :

    ffmpeg version 3.2.14-1~deb9u1 Copyright (c) 2000-2019 the FFmpeg developers
     built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
     configuration: --prefix=/usr --extra-version='1~deb9u1' --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libebur128 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
     libavutil      55. 34.101 / 55. 34.101
     libavcodec     57. 64.101 / 57. 64.101
     libavformat    57. 56.101 / 57. 56.101
     libavdevice    57.  1.100 / 57.  1.100
     libavfilter     6. 65.100 /  6. 65.100
     libavresample   3.  1.  0 /  3.  1.  0
     libswscale      4.  2.100 /  4.  2.100
     libswresample   2.  3.100 /  2.  3.100
     libpostproc    54.  1.100 / 54.  1.100
    [webm_dash_manifest @ 0x557f55dd1160] Could not find codec parameters for stream 0 (Video: vp9, none, 1280x534): unspecified pixel format
    Consider increasing the value for the 'analyzeduration' and 'probesize' options
    Input #0, webm_dash_manifest, from 'video.webm':
     Metadata:
       title           : Cloud Atlas
       ENCODER         : Lavf58.35.104
     Duration: 00:05:00.01, bitrate: 998 kb/s
       Chapter #0:0: start 0.000000, end 300.000000
       Metadata:
         title           : Chapter 01
       Stream #0:0(eng): Video: vp9, none, 1280x534, SAR 1:1 DAR 640:267, 23.98 fps, 23.98 tbr, 1k tbn, 1k tbc (default) (forced)
       Metadata:
         title           : Video @ 6.9 Mbps [frame B:188517 Avg QP:20.66]
         ENCODER         : Lavc58.66.100 libvpx-vp9
         DURATION        : 00:05:00.008000000
         webm_dash_manifest_duration: 300008
         webm_dash_manifest_initialization_range: 900
         webm_dash_manifest_file_name: video.webm
         webm_dash_manifest_track_number: 1
         webm_dash_manifest_cues_start: 37455991
         webm_dash_manifest_cues_end: 37457486
         webm_dash_manifest_bandwidth: 1420427
         webm_dash_manifest_cluster_keyframe: 1
         webm_dash_manifest_cue_timestamps: 298715
    Input #1, webm_dash_manifest, from 'audio.webm':
     Metadata:
       title           : Cloud Atlas
       ENCODER         : Lavf58.35.104
     Duration: 00:05:00.01, bitrate: 126 kb/s
       Chapter #1:0: start 0.000000, end 300.000000
       Metadata:
         title           : Chapter 01
       Stream #1:0(eng): Audio: opus, 48000 Hz, stereo, fltp (default)
       Metadata:
         title           : Audio Eng DTS 5.1 channels 24 bits @ 1509 Kbps cbr
         ENCODER         : Lavc58.66.100 libopus
         DURATION        : 00:05:00.007000000
         webm_dash_manifest_duration: 300007
         webm_dash_manifest_initialization_range: 838
         webm_dash_manifest_file_name: audio.webm
         webm_dash_manifest_track_number: 1
         webm_dash_manifest_cues_start: 4744091
         webm_dash_manifest_cues_end: 4745279
         webm_dash_manifest_bandwidth: 137531
         webm_dash_manifest_cluster_keyframe: 1
         webm_dash_manifest_cue_timestamps: 295000
    Input #2, webvtt, from 'subtitles.vtt':
     Duration: N/A, bitrate: N/A
       Stream #2:0: Subtitle: webvtt
    Could not write header for output file #0 (incorrect codec parameters ?): Operation not permittedStream mapping:
     Stream #0:0 -> #0:0 (copy)
     Stream #1:0 -> #0:1 (copy)
     Stream #2:0 -> #0:2 (copy)
       Last message repeated 1 times

    Note : [webm_dash_manifest @ 0x557f55dd1160] Could not find codec parameters for stream 0 (Video: vp9, none, 1280x534): unspecified pixel format is harmless according to this post.

    The subtitles have been extracted with ffmpeg :

    ffmpeg -i "Cloud Atlas.mkv" -map 0:6 -t 00:05:00 -c:s webvtt -dash 1 subtitles.vtt

    Thank you for reading my long post, I have no idea what to do next.

    EDIT : The WebM Project website says : ’Initial WebM release does not support subtitles’. Has someone heard of a new release ? Or a convenient way to create DASH manifest with subtitles ?