[mythtv-users] DVB subtitles and delay

[Mark Kendall]

On 13 April 2010 03:54, Martin <martin.rene.mortensen at gmail.com> wrote:
> MythTV has since the 0.22 ffmpeg sync not had great support for DVB
> subtitles. They are delayed - and this off course has very low WAF.
> Theres a bug report on it, fix is seemingly a somewhat large rewrite and has
> been postponed to 0.24 now.
> TRAC ticket 6753: http://svn.mythtv.org/trac/ticket/6753
> Now I am wondering if there is not a work-around of some sort. There was
> some suggestion that one could revert mpegts.c,h to one before the sync. But
> this is not a very viable solution if you lose important features like
> he-aac sound.
> Do anyone have work-arounds for this? or are very few people using DVB
> subtitles ?

For what it's worth, I spent some time looking at that ticket a few
weeks ago without much success.

The problem lies somewhere between the broadcaster and ffmpeg's
demuxing of the stream, with the net result that some subtitles arrive
very late. I worked with the patch that Janneg posted to the ticket
for queueing transmitted packets and that did generate some
improvements but it certainly did not fix it and was far from a
complete/commitable solution. There are various issues - though
ideally this would be fixed within ffmpeg itself. Overall there is no
simple fix that I can see that sits within the main MythTV code.

With respect to DVB subs in general, I'm quite sure that many people
are using them without issue. This particular issue seems to manifest
itself on one or more Northern European/Scandinavian transmissions
(judging by the test clips posted to trac) where the delay is large
enough to be noticeable/annoying. UK DVB subtitles, for example, seem
to be working OK - though the problem may just not be as pronounced.

regards

Mark