[FFmpeg-trac] #8684(ffmpeg:new): WebVTT decoder breaks when ::cue elements are used

FFmpeg trac at avcodec.org
Tue May 26 22:48:00 EEST 2020


#8684: WebVTT decoder breaks when ::cue elements are used
--------------------------------+--------------------------------------
             Reporter:  derrod  |                     Type:  defect
               Status:  new     |                 Priority:  minor
            Component:  ffmpeg  |                  Version:  git-master
             Keywords:  webvtt  |               Blocked By:
             Blocking:          |  Reproduced by developer:  0
Analyzed by developer:  0       |
--------------------------------+--------------------------------------
 Summary of the bug: WebVTT input is not read past `::cue` tags in input
 file.
 How to reproduce:
 {{{
 % ffmpeg -y -v 9 -loglevel 99 -i test_input.vtt test_output.ass
 ffmpeg version git-2020-05-25-6268034 Copyright (c) 2000-2020 the FFmpeg
 developers
   built with gcc 9.3.1 (GCC) 20200523
   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-libsrt --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-libvmaf --enable-libvorbis --enable-libvo-
 amrwbenc --enable-libmysofa --enable-libspeex --enable-libxvid --enable-
 libaom --disable-w32threads --enable-libmfx --enable-ffnvcodec --enable-
 cuda-llvm --enable-cuvid --enable-d3d11va --enable-nvenc --enable-nvdec
 --enable-dxva2 --enable-avisynth --enable-libopenmpt --enable-amf
   libavutil      56. 49.100 / 56. 49.100
   libavcodec     58. 87.101 / 58. 87.101
   libavformat    58. 43.100 / 58. 43.100
   libavdevice    58.  9.103 / 58.  9.103
   libavfilter     7. 83.100 /  7. 83.100
   libswscale      5.  6.101 /  5.  6.101
   libswresample   3.  6.100 /  3.  6.100
   libpostproc    55.  6.100 / 55.  6.100
 Splitting the commandline.
 Reading option '-y' ... matched as option 'y' (overwrite output files)
 with argument '1'.
 Reading option '-v' ... matched as option 'v' (set logging level) with
 argument '9'.
 Reading option '-loglevel' ... matched as option 'loglevel' (set logging
 level) with argument '99'.
 Reading option '-i' ... matched as input url with argument
 'test_input.vtt'.
 Reading option 'test_output.ass' ... matched as output url.
 Finished splitting the commandline.
 Parsing a group of options: global .
 Applying option y (overwrite output files) with argument 1.
 Applying option v (set logging level) with argument 9.
 Successfully parsed a group of options.
 Parsing a group of options: input url test_input.vtt.
 Successfully parsed a group of options.
 Opening an input file: test_input.vtt.
 [NULL @ 0000025fa3a9ccc0] Opening 'test_input.vtt' for reading
 [file @ 0000025fa3a9dd40] Setting default whitelist 'file,crypto,data'
 Probing webvtt score:100 size:139
 [webvtt @ 0000025fa3a9ccc0] Format webvtt probed with size=2048 and
 score=100
 [webvtt @ 0000025fa3a9ccc0] Before avformat_find_stream_info() pos: 44
 bytes read:139 seeks:0 nb_streams:1
 [webvtt @ 0000025fa3a9ccc0] All info found
 [webvtt @ 0000025fa3a9ccc0] stream 0: start_time: -9223372036854776.000
 duration: -9223372036854776.000
 [webvtt @ 0000025fa3a9ccc0] format: start_time: -9223372036854.775
 duration: -9223372036854.775 (estimate from bit rate) bitrate=0 kb/s
 [webvtt @ 0000025fa3a9ccc0] After avformat_find_stream_info() pos: 44
 bytes read:139 seeks:0 frames:0
 Input #0, webvtt, from 'test_input.vtt':
   Duration: N/A, bitrate: N/A
     Stream #0:0, 0, 1/1000: Subtitle: webvtt
 Successfully opened the file.
 Parsing a group of options: output url test_output.ass.
 Successfully parsed a group of options.
 Opening an output file: test_output.ass.
 [file @ 0000025fa3aa1b80] Setting default whitelist 'file,crypto,data'
 Successfully opened the file.
 Output #0, ass, to 'test_output.ass':
   Metadata:
     encoder         : Lavf58.43.100
     Stream #0:0, 0, 1/100: Subtitle: ass (ssa)
     Metadata:
       encoder         : Lavc58.87.101 ssa
 Stream mapping:
   Stream #0:0 -> #0:0 (webvtt (native) -> ass (ssa))
 Press [q] to stop, [?] for help
 cur_dts is invalid st:0 (0) [init:1 i_done:0 finish:0] (this is harmless
 if it occurs once at the start per stream)
 No more output streams to write to, finishing.
 size=       1kB time=00:00:00.00 bitrate=N/A speed=   0x
 video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:1kB
 muxing overhead: unknown
 Input file #0 (test_input.vtt):
   Input stream #0:0 (subtitle): 0 packets read (0 bytes); 0 frames
 decoded;
   Total: 0 packets (0 bytes) demuxed
 Output file #0 (test_output.ass):
   Output stream #0:0 (subtitle): 0 frames encoded; 0 packets muxed (0
 bytes);
   Total: 0 packets (0 bytes) muxed
 0 frames successfully decoded, 0 decoding errors
 [AVIOContext @ 0000025fa3aa2d40] Statistics: 0 seeks, 1 writeouts
 [AVIOContext @ 0000025fa3aa5fc0] Statistics: 139 bytes read, 0 seeks

 }}}

 The entire content of the input file is as follows (also attached):
 {{{
 WEBVTT

 ::cue(.white){ color: white; }

 1
 00:00:01.000 --> 00:00:05.000 line:77% position:50% align:middle
 <c.white>Hello World</c>
 }}}

 The output file only contains the boilerplate ASS information and no
 events. (see attached file).

 Removing the line(s) starting with `::cue` will result in a successfully
 converted output (albeit without the styling).

 Note that even a codec copy from WebVTT to WebVTT will fail and produce an
 output file that contains only the "WEBVTT" header (other attached file).

--
Ticket URL: <https://trac.ffmpeg.org/ticket/8684>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker


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