[FFmpeg-devel] BUG in use of extradata and extradata_size with dvb subtitles and teletext

Clément Bœsch u at pkh.me
Mon Dec 30 13:50:32 CET 2013

On Mon, Dec 30, 2013 at 11:53:48AM +0200, Andriy Lysnevych wrote:
> Hi,
> We are almost done with patch that fixes DVB subtitles and teletext issues.
> We are doing 2 things in this patch:
> 1) Removing dependency on extradata. All the values that currently stored
> in extradatata will be generated from metadata. For example in case of DVB
> subtitles metadata will hold the following values:
> language
> subtitling_type
> composition_page_id
> ancillary_page_id
> This values will be used for correct PMT generation. The values can be
> comma separated because one DVB subtitle stream can carry few subtitle
> substreams of different language, type, etc.
> a) In case of copy scenario the values will be copied from metadata of
> MPEGTS demuxer subtitle stream to metadata of MPEGTS muxer subtitle stream.
> b) In case when you generate subtitles (i.e. using FFmpeg libraries and DVB
> subtitles encoder) you should set the fields in metadata correctly for
> output subtitles stream of MPEGTS muxer otherwise default values will be
> used.
> 2) Currently there 2 different formats of DVB subtitles payload in
> AVPacket.data. Fore details you can read this thread
> https://trac.ffmpeg.org/ticket/2989
> We are fixing FFmpeg so only one common format of DVB subtitles will be
> used across all the components. AVPacket payload of DVB subtitles will
> contain all the fields from standard:
> data_identifier 8bit - always set to 0x20
> subtitle_stream_id 8bit - always set to 0x00
> subtitling_segments - actual payload
> end_of_PES_data_field_makrer 8bit - always set to 0xFF

> Feel free to ask any questions.

Can we see the patch, even if it's a work in progress? What's remaining?
I'm uncertain about using metadata for the information you're trying to
transmit: typical problem is that it will be transmitted to the muxer.
Typically you might end up with a format adding strings metadata in the
destination format if it doesn't understand them.

Clément B.
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