[Spice-devel] [PATCH spice-gtk v4 5/7] display-gst: check GstRegistry for decoding elements

[Pavel Grunt]

On Wed, 2017-06-28 at 14:43 +0200, Victor Toso wrote:
> From: Victor Toso <me at victortoso.com>
> 
> With this patch, we can find all the elements in the registry that are
> video decoders which can handle the predefined GstCaps.
> 
> Main benefits are:
> - We don't rely on a predefined list of GstElements. We don't need to
>   update them;
> - debugging: It does help to know what the registry has at runtime;
> 
> Signed-off-by: Victor Toso <victortoso at redhat.com>
> Acked-by: Frediano Ziglio <fziglio at redhat.com>
> Signed-off-by: Victor Toso <me at victortoso.com>
> ---
>  src/channel-display-gst.c | 56 ++++++++++++++++++++++++++++++++++++++++++--
> ---
>  1 file changed, 50 insertions(+), 6 deletions(-)
> 
> diff --git a/src/channel-display-gst.c b/src/channel-display-gst.c
> index 57f0eb7..1b40002 100644
> --- a/src/channel-display-gst.c
> +++ b/src/channel-display-gst.c
> @@ -521,16 +521,60 @@ VideoDecoder* create_gstreamer_decoder(int codec_type,
> display_stream *stream)
>      return (VideoDecoder*)decoder;
>  }
>  
> +static void gstvideo_debug_available_decoders(int codec_type,
> +                                              GList *all_decoders,
> +                                              GList *codec_decoders)
> +{
> +    GList *l;
> +    GString *msg = g_string_new(NULL);
> +    /* Print list of available decoders to make debugging easier */
> +    g_string_printf(msg, "From %3u video decoder elements, %2u can handle
> caps %12s: ",
> +                    g_list_length(all_decoders),
> g_list_length(codec_decoders),
> +                    gst_opts[codec_type].dec_caps);
> +
> +    for (l = codec_decoders; l != NULL; l = l->next) {
> +        GstPluginFeature *pfeat = GST_PLUGIN_FEATURE(l->data);
> +        g_string_append_printf(msg, "%s, ",
> gst_plugin_feature_get_name(pfeat));
> +    }
> +
> +    /* Drop trailing ", " */
> +    g_string_truncate(msg, msg->len - 2);
> +    spice_debug("%s", msg->str);
> +    g_string_free(msg, TRUE);
> +}
> +
>  G_GNUC_INTERNAL
>  gboolean gstvideo_has_codec(int codec_type)
>  {
> -    gboolean has_codec = FALSE;
> +    GList *all_decoders, *codec_decoders;
> +    GstCaps *caps;
> +    GstElementFactoryListType type;
> +
> +    g_return_val_if_fail(gstvideo_init(), FALSE);
> +    g_return_val_if_fail(VALID_VIDEO_CODEC_TYPE(codec_type), FALSE);
>  
> -    VideoDecoder *decoder = create_gstreamer_decoder(codec_type, NULL);
> -    if (decoder) {
> -        has_codec = TRUE;
> -        decoder->destroy(decoder);
> +    type = GST_ELEMENT_FACTORY_TYPE_DECODER |
> GST_ELEMENT_FACTORY_TYPE_MEDIA_VIDEO;

also GST_ELEMENT_FACTORY_TYPE_MEDIA_IMAGE for "image/jpeg"

> +    all_decoders = gst_element_factory_list_get_elements(type,
> GST_RANK_NONE);
> +    if (all_decoders == NULL) {
> +        spice_warning("No video decoders from GStreamer were found");
> +        return FALSE;
>      }
>  
> -    return has_codec;
> +    caps = gst_caps_from_string(gst_opts[codec_type].dec_caps);
> +    codec_decoders = gst_element_factory_list_filter(all_decoders, caps,
> GST_PAD_SINK, TRUE);
> +    gst_caps_unref(caps);
> +
> +    if (codec_decoders == NULL) {
> +        spice_debug("From %u decoders, none can handle '%s'",
> +                    g_list_length(all_decoders),
> gst_opts[codec_type].dec_caps);
> +        gst_plugin_feature_list_free(all_decoders);
> +        return FALSE;
> +    }
> +
> +    if (spice_util_get_debug())
> +        gstvideo_debug_available_decoders(codec_type, all_decoders,
> codec_decoders);
> +
> +    gst_plugin_feature_list_free(codec_decoders);
> +    gst_plugin_feature_list_free(all_decoders);
> +    return TRUE;
>  }