[Spice-devel] [PATCH spice-gtk] gst: Fix detection of h264 stream decoder

[Victor Toso]

Hi,

On Wed, Jul 19, 2017 at 02:59:00PM +0200, Pavel Grunt wrote:
> GStreamer's avdec_h264 needs h264parse to be able to process H264 video
> streams. However the check for elements through GstRegistry does not
> take into account the possible pipeline of elements (like "h264parse ! avdec_h264").
>
> Fix that by checking for the elements by their name.

As I mentioned before, given the extra complexity that this is
requiring, I'm not convinced that it is a good fix because it relies on
the fact that we know the elements that we need (hard coded).

1-) An user might have a different subset of plugins, like the fluendo
    ones or a different 3rd party ones. Do that work when we check for
    h264parse avdec_h264? I don't think so as it should be different
    plugins (one that people pay to have in their system)

2-) If playbin just needs an extra plugin, we don't check it and that
    means the pipeline will fail even if the caps were enabled.

I do think the right approach is as I mentioned before, fix the
filtering to show all decoders for h264 and that's it. If the pipeline
fails, that's fine because it is *hard* to *ensure* that it'll work
anyway without an actual video stream.

> ---
>  src/channel-display-gst.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
>
> diff --git a/src/channel-display-gst.c b/src/channel-display-gst.c
> index 5042fc8..a9a044a 100644
> --- a/src/channel-display-gst.c
> +++ b/src/channel-display-gst.c
> @@ -666,6 +666,31 @@ gboolean gstvideo_has_codec(int codec_type)
>      codec_decoders = gst_element_factory_list_filter(all_decoders, caps, GST_PAD_SINK, TRUE);
>      gst_caps_unref(caps);
>
> +    /* Check for the presence of decoding elements that could be filter out.
> +     * TODO: Improve filtering to avoid this...
> +     */
> +    {
> +        GList *decoder_elements = NULL;
> +        gchar **decoders_by_names;
> +        guint i = 0;
> +        decoders_by_names = g_strsplit(gst_opts[codec_type].dec_name, "!", -1);
> +        for (i = 0; decoders_by_names[i] != NULL; i++) {
> +            GstElementFactory *element = gst_element_factory_find(g_strstrip(decoders_by_names[i]));
> +            if (element == NULL) {
> +                gst_plugin_feature_list_free(decoder_elements);
> +                decoder_elements = NULL;
> +                break;
> +            }
> +            if (g_list_find(codec_decoders, element)) {
> +                gst_object_unref(element);
> +            } else {
> +                decoder_elements = g_list_append(decoder_elements, element);
> +            }
> +        }
> +        codec_decoders = g_list_concat(codec_decoders, decoder_elements);
> +        g_strfreev(decoders_by_names);
> +    }
> +
>      if (codec_decoders == NULL) {
>          spice_debug("From %u decoders, none can handle '%s'",
>                      g_list_length(all_decoders), gst_opts[codec_type].dec_caps);
> -- 
> 2.13.3
> 
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