[Fwd: Re: [gst-devel] Subtitle support in 0.10]

Wim Taymans wim at fluendo.com
Fri Dec 16 08:47:07 CET 2005

-------- Forwarded Message --------
From: Wim Taymans <wim at fluendo.com>
To: Michal Benes <michal.benes at xeris.cz>
Subject: Re: [gst-devel] Subtitle support in 0.10
Date: Fri, 16 Dec 2005 17:45:41 +0100

On Fri, 2005-12-16 at 17:06 +0100, Michal Benes wrote:
> Hi all,
> 	I want to add support for subtitles to matroska muxer. The problem is
> that filler events have been (temporarily) removed and if I understand
> it well there not yet consensus how to handle sparse streams (especially
> in collectpads).
> 	May be, a good solution would be to introduce empty "filler buffers"
> instead of events. As a temporary hack I plan to push an empty buffer to
> the pipeline every second (and drop empty buffers in matroska muxer).


If you know when (in time T) the first subtitle will be produced you can
push an empty subtitle buffer (representing a subtitle without text)
with timestamp 0 and duration T, then a filled subtitle buffer with
timestamp T and the duration of the subtitle, then again an empty buffer
at time T1 (when the subtitle should be removed) etc... This would
effectively make the subtitle stream a continuous stream. I believe most
subtitle file formats provide this information.

If you don't know the positions of the subtitles (some muxed formats?,
mpeg for sure) sending an empty subtitle buffer at regular times might
do the trick. I don't consider this more of a hack then sending filler
events every now and then and makes it easier to deal with for elements
since they don't have to combine events and buffers to reconstruct a
continuous stream. The granularity of subtitle display would of course
be the frequency at which you push out these empty buffers.

Another option is to mark pads on collectpads as sparse so that they
don't block collecting of the other pads. If data arrives on such sparse
pads, it can be collected.  


> 	What are your thoughts on this?
> 		Michal
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Wim Taymans <wim at fluendo.com>

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