[Spice-devel] [spice-gtk v1 3/4] channel-display-gst: improve check for decoder element

[Victor Toso]

Hi,

On Wed, Oct 19, 2016 at 06:26:18PM +0200, Francois Gouget wrote:
> On Wed, 19 Oct 2016, Victor Toso wrote:
> [...]
> > > But I don't think this necessarily impacts gstvideo_has_codec() if
> > > implemented using create_gstreamer_decoder() whereas with your code it
> > > will necessarily be impacted.
> >
> > Well, my point is simply why create the whole pipeline if we only need
> > to check if element is present. As I said above, it might even be enough
> > to check if we have hw decoding by adding vaapijpegdec, vaapih264dec,
> > and so on.
>
> So gstvideo_has_codec() will have to know about vaapijpegdec,
> vaapih264dec, and so on. And create_gstreamer_decoder() will need to
> know about them too. Whereas with the current code only
> create_gstreamer_decoder() has to know about them.
>
> > Once again, I don't really mind to drop this patch, I just want to
> > understand why it is error prone / not reliable.
>
> It relies on GStreamer elements being 'visible' only if their resources
> are available which is not how GStreamer worked up to August 2016
> (1.8.3). That it works this way in 1.9 for the vaapi set of decoders is
> nice, but will it be true of other hardware decoders too?

That's a good question. So, the current code makes it possible to detect
hw decoding for more versions of gstreamer... sounds good reason to me.

>
> Also are we sure we will not want to support hardware decoding with
> GStreamer 1.8? 1.8.3 is only a few months old.
>
> But really I don't see any tangible benefit to this change so I'm in
> favor of keeping the code simple.

I do. For me it seems simpler checking if an element exist instead of
creating the whole pipeline and then dropping it.

I'll remove this change for now and send a v2 with the other requested
changes.

Many thanks for the review and discussion,
  toso
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