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

JULIAN GARDNER joolzg at btinternet.com
Mon Dec 30 15:24:07 CET 2013

> From: Clément Bœsch <u at pkh.me>
>To: FFmpeg development discussions and patches <ffmpeg-devel at ffmpeg.org> 
>Cc: serhii.marchuk at gmail.com 
>Sent: Monday, 30 December 2013, 13:50
>Subject: Re: [FFmpeg-devel] BUG in use of extradata and extradata_size with dvb subtitles and teletext
>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.
>ffmpeg-devel mailing list
>ffmpeg-devel at ffmpeg.org

Please can we see your patches as I would like to make sure all the work i have done wont be wasted for one.

Also want to check some of the problems i found and fixed as as the moment the only thing not working is the dvbsubs copy


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