Subtitle: TTML support

[3052]

I have the below file, the subtitles will not load

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'out.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf60.16.100
  Duration: 01:38:48.75, start: 0.000000, bitrate: 3957 kb/s
  Stream #0:0[0x1](und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(progressive), 1200x720 [SAR 1:1 DAR 5:3], 3822 kb/s, 24 fps, 24 tbr, 19200 tbn (default)
    Metadata:
      handler_name    : USP Video Handler
      vendor_id       : [0][0][0][0]
      encoder         : AVC Coding
  Stream #0:1[0x2](zho): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 127 kb/s (default)
    Metadata:
      handler_name    : USP Sound Handler
      vendor_id       : [0][0][0][0]
  Stream #0:2[0x3](eng): Subtitle: ttml (stpp / 0x70707473), 1 kb/s (default)
    Metadata:
      handler_name    : USP Subtitle Handler

[pkoshevoy]

@3052 Is there a publicly available sample file with this subtitle type?
Does this subtitle type work with any known player (vlc or ffplay)?

[3052]

https://github.com/pkoshevoy/aeyae/files/14601290/af343964d7-textstream_eng.1000.zip

it works with VLC

[pkoshevoy]

@3052 ffmpeg doesn't have a decoder for ttml, and as my player depends on ffmpeg API for demuxing/decoding -- ttml subtitles most likely are not going to be supported until they are supported by ffmpeg.

ffplay version N-114162-g2129d66a66 Copyright (c) 2003-2024 the FFmpeg developers
  built with Apple clang version 14.0.0 (clang-1400.0.29.202)
  configuration: --prefix=/Users/pavel/x86_64 --disable-debug --enable-libx264 --enable-libzimg --enable-libass --enable-libbluray --enable-libmodplug --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-runtime-cpudetect --extra-cflags=-I/opt/local/include --extra-ldflags='-headerpad_max_install_names -L/opt/local/lib'
  libavutil      59.  1.100 / 59.  1.100
  libavcodec     61.  1.101 / 61.  1.101
  libavformat    61.  0.100 / 61.  0.100
  libavdevice    61.  0.100 / 61.  0.100
  libavfilter    10.  0.100 / 10.  0.100
  libswscale      8.  0.100 /  8.  0.100
  libswresample   5.  0.100 /  5.  0.100
  libpostproc    58.  0.100 / 58.  0.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/tmp/out.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf61.0.100
  Duration: 03:53:20.06, start: 0.000000, bitrate: 1331 kb/s
  Stream #0:0[0x1](und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 159 kb/s (default)
      Metadata:
        handler_name    : SoundHandler
        vendor_id       : [0][0][0][0]
  Stream #0:1[0x2](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, smpte170m/smpte170m/bt709, progressive), 720x480 [SAR 8:9 DAR 4:3], 1165 kb/s, 23.98 fps, 23.98 tbr, 16k tbn (default)
      Metadata:
        handler_name    : VideoHandler
        vendor_id       : [0][0][0][0]
  Stream #0:2[0x3](eng): Subtitle: ttml (stpp / 0x70707473), 1 kb/s (default)
      Metadata:
        handler_name    : USP Subtitle Handler
No decoder could be found for codec ttml
   7.61 A-V: -0.002 fd=   1 aq=   34KB vq=   13KB sq=    0B 

[3052]

yeah, seems like support for TTML is pretty crappy at this time, missing from FFmpeg and MPV. as a workaround, it seems WebVTT is pretty common with better support:

• https://ffmpeg.org/ffmpeg-all.html#Subtitle-Formats
• https://wikipedia.org/wiki/WebVTT