[vlc-devel] [Patch] Sending a signal when a vout is created/destroyed

[Rémi Denis-Courmont]

Le mardi 26 janvier 2010 22:04:25 Laurent Aimar, vous avez écrit :
> > <beauze.h at gmail.com> wrote:
> > > This patchs adds a libvlc_MediaPlayerVoutChanged event, that let an
> > > application using libvlc know when a vout has been created.
> > > This can be usefull when trying to know the width or height of a
> > > media, using libvlc_video_get_width/height, as these functions
> > > immediatly return when no vout has been spawned.
> >
> > It's none of the LibVLC application business when a video output is
> > created; that's an internal implementation detail. It should only care
> > that there is a new elementary stream. Hence I think that event does not
> > deserve to exist.
> 
>  I don't agree (completly) with you. It is usefull to know when a vout
> exists to know when to present some options to the users like:
>  - snapshot.
>  - video filters.
>  - deinterlace configurations.

Snapshot maybe. But configuring video filters in general and deinterlacing in 
particular shouldn't be dependent on the existence video output. That just 
creates more unnecessary event handling boilerplate for each and every LibVLC-
based application.

To me, the fact that so many video and audio functions in the LibVLC API fail 
or misbehave if the video or audio output does not (yet) exist is a bug and an 
annoyance. And in fact, there is absolutely no fundamental reason for those 
limitations to exist. For instance, we can the video-filter variables on the 
input (or even the instance) object. And *if* there is an active video output, 
then we can also tell it to update its current state. But most video and audio 
settings should be settable (and gettable) even without an output.

Snapshots are an exception rather than a rule. They obviously don't make sense 
if there is no video output. Selecting the active audio ES, or getting the 
video resolution are "intermediate" exception as far as they require the ES to 
exist, but not necessarily the final output.

-- 
Rémi Denis-Courmont
http://www.remlab.net/
http://fi.linkedin.com/in/remidenis