textoverlay and overlapping subtitles

[Jérôme Laheurte]

> Le 27 nov. 2016 à 17:45, Nicolas Dufresne <nicolas.dufresne at gmail.com> a écrit :
> 
> Le dimanche 27 novembre 2016 à 13:42 +0100, Jérôme Laheurte a écrit :
>> It looks like textoverlay can only display one text buffer « at a
>> time »; when several subtitle strings should be displayed it just
>> keeps displaying the first it received, until it’s no longer valid
>> (gstbasetextoverlay.c:2575). I have several videos in which people
>> are talking while a sign is displayed and I often miss half the
>> dialogue because of this. Is there an existing fix/workaround? If not
>> I can try my hand at this. I can see two ways of doing it:
> 
> Yes, see https://bugzilla.gnome.org/show_bug.cgi?id=540131

Thanks; my search-fu seems to be rusty.

> 
>> 
>> 1. Change textoverlay to hold a liked list of currently valid text
>> buffers instead of just the latest one, and compose them before
>> rendering.
>> 2. Create a new « subtitlecompose » element that receives text
>> buffers, does the composition, and outputs text buffers containing
>> all currently valid strings.
>> 
>> The obvious advantage of 2 is that it will work with any combination
>> of text overlay / source elements. May be a bit tricky to use in a
>> playbin though; I guess I could use the text-sink property for that.
>> The problem is that is will rely on textoverlay doing the opposite of
>> what it’s doing right now and discard the existing buffer as soon as
>> it receives a new one. Thoughts?
> 
> It should manage it's own linked list. The reason is because text-
> overlay still need to manage the text placement. If we follow how
> assrender works, we'll be stacking up or down (depending on the
> location of the overlay) each text. So they form paragraphs. When there
> is two strings and one expires, the element need to update the old one,
> as it's position may change (or not). This obviously depends on the
> rules we want to follow of course, but in general, I believe that if
> the screen get saturated, you want to pop out the oldest one. A good
> start point would be to look at what assrender is doing.

Okay, I’ll take a look next week-end.

> 
> The idea of having a downstream element composing the overlay is
> something I have discussed already with few people. Though, we already
> have an element that can handle this, it's called compositor. The
> blending operation are the same, it's really a matter of extracting,
> converting and caching the overlay buffers. Same apply to glvideomixer.

Maybe a bit much for someone who only occasionally fiddles with GStreamer code :)

Best regards
Jérôme Laheurte

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 842 bytes
Desc: Message signed with OpenPGP using GPGMail
URL: <https://lists.freedesktop.org/archives/gstreamer-devel/attachments/20161128/70a773ec/attachment.sig>