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

[Andriy Lysnevych]

We modified only MPEG-TS muxer and DVB subtitles encoder. No changes in
MPEG-TS demuxer, DVB subtitles parser and DVB subtitles decoder.


On Thu, Jan 9, 2014 at 3:40 PM, Reimar Döffinger
<Reimar.Doeffinger at gmx.de>wrote:

>
>
> On 08.01.2014, at 23:01, Michael Niedermayer <michaelni at gmx.at> wrote:
>
> > On Wed, Jan 08, 2014 at 05:33:59PM +0100, Michael Niedermayer wrote:
> >> On Wed, Jan 08, 2014 at 06:15:19PM +0200, Andriy Lysnevych wrote:
> >>> Any way we must fix this bug at some point. Having two DVB subtitle
> formats
> >>> in FFmpeg already caused a lot of related issues.
> >>>
> >>> Applying only libavcodec change will break DVB subtitle encoder ->
> MPEG-TS
> >>> muxer chain and as the result output MPEG-TS stream will contain
> malformed
> >>> DVB subtitle payload.
> >>>
> >>> To keep compatibility we can check version of libavformat in DVB
> subtitle
> >>> encoder and add beginning 0x00 and trailing 0xFF bytes for older
> versions
> >>> as it was before. To do so we must increase version of libavformat with
> >>> this patch.
> >>>
> >>> Questions are:
> >>
> >>> 1) How to detect libavformat version from libavcodec? Is calling
> >>> avformat_version() ok?
> >>
> >> no
> >> libavcodec has no way to detect the libavformat its used with or even
> >> if its used with any libavformat or different code.
> >>
> >> I think there are only 2 (reasonable) solutions
> >> A. what ubitux suggested, that a option is added and the default stays
> >>   the old format and the application would have to set it to have
> >>   the new format used
> >> B. just accept that the format was buggy&broken and that this is a bug
> >>   fix
> >>
> >> Did any application use / depend on this specific "buggy" format ?
> >>
> >
> >> I think ubitux and any application developers affected by this are
> >> the best to decide of B. is acceptable
> >
> > and if noone replies then you can probably assume its ok and noone
> > knows of any code that depends on this format
>
> If only the format the encoder creates is changed that probably is fine, I
> am not aware of any application using the encoder.
> However for the decoder compatibility is important, since to my knowledge
> several players use it with their won demuxers instead of libavformat.
> Am I correct that the patch only changes encoder and muxer?
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