Opened 3 years ago

Last modified 8 weeks ago

#9064 new enhancement

WebVTT decoder truncates files with STYLE blocks

Reported by: Roderich Schupp Owned by:
Priority: wish Component: avformat
Version: git-master Keywords: webvtt
Cc: August Wikerfors, nathanielcwm Blocked By:
Blocking: Reproduced by developer: no
Analyzed by developer: no

Description

If a webvtt file contains STYLE blocks, the webvtt decoder truncates the file at the first such block. Since these blocks typically occur at the top of the webvtt file, this results in an empty file (except for the WEBVTT header line).

Note: This may be related to #8684, though the sample webvtt attached there is invalid.

How to reproduce:

$ ffmpeg -y -v 9 -loglevel 99 -i sample_in.vtt -c copy sample_out.vtt
ffmpeg version 4.3.1-5 Copyright (c) 2000-2020 the FFmpeg developers

built with gcc 10 (Debian 10.2.0-15)
configuration: --prefix=/usr --extra-version=5 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libdav1d --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librabbitmq --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --disable-libsrt --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-pocketsphinx --enable-libmfx --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared
WARNING: library configuration mismatch
avcodec configuration: --prefix=/usr --extra-version=5 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --arch=amd64 --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libdav1d --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librabbitmq --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --disable-libsrt --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opencl --enable-opengl --enable-sdl2 --enable-pocketsphinx --enable-libmfx --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared --enable-version3 --disable-doc --disable-programs --enable-libaribb24 --enable-liblensfun --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libtesseract --enable-libvo_amrwbenc
libavutil 56. 51.100 / 56. 51.100
libavcodec 58. 91.100 / 58. 91.100
libavformat 58. 45.100 / 58. 45.100
libavdevice 58. 10.100 / 58. 10.100
libavfilter 7. 85.100 / 7. 85.100
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 7.100 / 5. 7.100
libswresample 3. 7.100 / 3. 7.100
libpostproc 55. 7.100 / 55. 7.100

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 'sample_in.vtt'.
Reading option '-c' ... matched as option 'c' (codec name) with argument 'copy'.
Reading option 'sample_out.vtt' ... 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 sample_in.vtt.
Successfully parsed a group of options.
Opening an input file: sample_in.vtt.
[NULL @ 0x5569603be0c0] Opening 'sample_in.vtt' for reading
[file @ 0x5569603beb80] Setting default whitelist 'file,crypto,data'
Probing webvtt score:100 size:362
[webvtt @ 0x5569603be0c0] Format webvtt probed with size=2048 and score=100
[webvtt @ 0x5569603be0c0] Before avformat_find_stream_info() pos: 55 bytes read:362 seeks:0 nb_streams:1
[webvtt @ 0x5569603be0c0] All info found
[webvtt @ 0x5569603be0c0] stream 0: start_time: NOPTS duration: NOPTS
[webvtt @ 0x5569603be0c0] format: start_time: NOPTS duration: NOPTS (estimate from bit rate) bitrate=0 kb/s
[webvtt @ 0x5569603be0c0] After avformat_find_stream_info() pos: 55 bytes read:362 seeks:0 frames:0
Input #0, webvtt, from 'sample_in.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 sample_out.vtt.
Applying option c (codec name) with argument copy.
Successfully parsed a group of options.
Opening an output file: sample_out.vtt.
[file @ 0x5569603c4140] Setting default whitelist 'file,crypto,data'
Successfully opened the file.
Output #0, webvtt, to 'sample_out.vtt':

Metadata:

encoder : Lavf58.45.100
Stream #0:0, 0, 1/1000: Subtitle: webvtt

Stream mapping:

Stream #0:0 -> #0:0 (copy)

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= 0kB time=00:00:00.00 bitrate=N/A speed= 0x
video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
Input file #0 (sample_in.vtt):

Input stream #0:0 (subtitle): 0 packets read (0 bytes);
Total: 0 packets (0 bytes) demuxed

Output file #0 (sample_out.vtt):

Output stream #0:0 (subtitle): 0 packets muxed (0 bytes);
Total: 0 packets (0 bytes) muxed

Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)
0 frames successfully decoded, 0 decoding errors
[AVIOContext @ 0x5569603c43c0] Statistics: 0 seeks, 1 writeouts
[AVIOContext @ 0x5569603c6fc0] Statistics: 362 bytes read, 0 seeks

Attachments (2)

sample_in.vtt (362 bytes ) - added by Roderich Schupp 3 years ago.
(input) sample WebVTT file with STYLE blocks
sample_out.vtt (7 bytes ) - added by Roderich Schupp 3 years ago.
(output) result of "ffmpeg -i sample_in.vtt -c copy sample_out.txt"

Download all attachments as: .zip

Change History (8)

by Roderich Schupp, 3 years ago

Attachment: sample_in.vtt added

(input) sample WebVTT file with STYLE blocks

by Roderich Schupp, 3 years ago

Attachment: sample_out.vtt added

(output) result of "ffmpeg -i sample_in.vtt -c copy sample_out.txt"

comment:1 by anonymous_coward, 2 years ago

I proposed a patch to fix this (and also write STYLE blocks out), but it has had no traction. Feel free to pile in on the thread.

https://patchwork.ffmpeg.org/project/ffmpeg/patch/CA+_k4RJ1CNriPbhxxzLf1O6V1VuP2OXch3E8LqOsMNSRUyEnTw@mail.gmail.com/

comment:2 by Carl Eugen Hoyos, 16 months ago

Priority: normalwish
Type: defectenhancement

See also #9609

comment:3 by anonymous_coward, 16 months ago

Is this really simply an enhancement? Even if styles aren't supported, total loss of captions seems like a defect to me. Either processing or just ignoring STYLE blocks would solve this issue.

The patch above (and at least one other submitted some time ago) addresses this issue directly - would it be possible for it to be reviewed please?

comment:4 by August Wikerfors, 8 months ago

Cc: August Wikerfors added

in reply to:  3 comment:5 by Cqoicebordel, 2 months ago

Replying to anonymous_coward:

Is this really simply an enhancement? Even if styles aren't supported, total loss of captions seems like a defect to me. Either processing or just ignoring STYLE blocks would solve this issue.

The patch above (and at least one other submitted some time ago) addresses this issue directly - would it be possible for it to be reviewed please?

Agreed. It's flabbergasting to have a 0k file or a file just with an header when converting from vtt to anything else, with only this error message :

Output file is empty, nothing was encoded(check -ss / -t / -frames parameters if used)

At least having a good error message would be helpful. Converting to a file without style would be welcome though.
(And converting with style, even the basics (bg/fg colors + align) would be ideal, but that's another FR)

comment:6 by nathanielcwm, 8 weeks ago

Cc: nathanielcwm added
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