SRC caps negotiation

[Tim Müller]

Hi Peter,

you don't need a query or event function on the src pad, it's much simpler: before you output your header buffers you do a gst_pad_get_allowed_caps(), and if the result is not fixed you truncate the caps to the first caps structure, and there you have your output caps.

Cheers
 -Tim

----- Original message -----
> Hi,
> 
> despite having read
> http://gstreamer.freedesktop.org/data/doc/gstreamer/head/pwg/html/section-nego-usecases.html
> I still don't get the details of the caps negotiation right.
> 
> I want to fix bug https://bugzilla.gnome.org/show_bug.cgi?id=735627, 
> that means implement two different wav formats depending on the 
> negotiated output format of the wavenc plug-in with a preference to the 
> current "audio/x-wav".
> 
> I thought, that in the code below I could get the proposed format and 
> set the preferred one in "gst_wavenc_src_setcaps". But the if clause in 
> this function is never entered.
> 
> Any pointer welcome,
> 
> Peter
> 
> 
> 
> diff --git a/gst/wavenc/gstwavenc.c b/gst/wavenc/gstwavenc.c
> index 4bcccf2..a2fd310 100644
> --- a/gst/wavenc/gstwavenc.c
> +++ b/gst/wavenc/gstwavenc.c
> @@ -96,6 +96,9 @@ typedef struct
>             "rate = (int) [ 8000, 192000 ], "       \
>             "channels = (int) [ 1, 2 ]"
> 
> +#define SRC_CAPS \
> +       "audio/x-wav; " \
> +       "audio/x-rf64"
> 
>     static GstStaticPadTemplate sink_factory = GST_STATIC_PAD_TEMPLATE 
> ("sink",
>             GST_PAD_SINK,
> @@ -106,7 +109,7 @@ static GstStaticPadTemplate sink_factory = 
> GST_STATIC_PAD_TEMPLATE ("sink",
>     static GstStaticPadTemplate src_factory = GST_STATIC_PAD_TEMPLATE
> ("src",           GST_PAD_SRC,
>             GST_PAD_ALWAYS,
> -       GST_STATIC_CAPS ("audio/x-wav")
> +       GST_STATIC_CAPS (SRC_CAPS)
>             );
> 
>     #define gst_wavenc_parent_class parent_class
> @@ -122,6 +125,7 @@ static gboolean gst_wavenc_event (GstPad * pad, 
> GstObject * parent,
>     static GstStateChangeReturn gst_wavenc_change_state (GstElement *
> element,           GstStateChange transition);
>     static gboolean gst_wavenc_sink_setcaps (GstPad * pad, GstCaps * caps);
> +static gboolean gst_wavenc_src_setcaps (GstPad *pad,   GstObject 
> *parent, GstEvent *event );
> 
>     static void
>     gst_wavenc_class_init (GstWavEncClass * klass)
> @@ -144,6 +148,46 @@ gst_wavenc_class_init (GstWavEncClass * klass)
>         GST_DEBUG_CATEGORY_INIT (wavenc_debug, "wavenc", 0, "WAV encoder 
> element");
>     }
> 
> +static gboolean
> +gst_wavenc_src_query (GstPad * pad, GstObject * parent, GstQuery *
> query) +{
> +   GstWavEnc *wavenc;
> +   gboolean ret = FALSE;
> +
> +   wavenc = GST_WAVENC (parent);
> +
> +   GST_DEBUG_OBJECT (wavenc, "Got %s query on pad %s: %s",
> +           GST_QUERY_TYPE_NAME (query), GST_DEBUG_PAD_NAME (pad));
> +
> +   switch (GST_QUERY_TYPE (query)) {
> +       case GST_QUERY_CAPS:
> +       {
> +           GstCaps *caps, *filter;
> +           GstStaticCaps staticCaps = GST_STATIC_CAPS (SRC_CAPS);
> +
> +           /* caps = gst_pad_get_allowed_caps (wavenc->srcpad); */
> +           caps = gst_static_caps_get (&staticCaps);
> +           GST_DEBUG_OBJECT (wavenc, "allowed %" GST_PTR_FORMAT, caps);
> +           gst_query_parse_caps (query, &filter);
> +           if (filter) {
> +               GstCaps *temp = gst_caps_intersect (caps, filter);
> +               gst_caps_unref (caps);
> +               caps = temp;
> +               GST_DEBUG_OBJECT (wavenc, "filtered %" GST_PTR_FORMAT, caps);
> +           }
> +           gst_query_set_caps_result (query, caps);
> +           gst_caps_unref (caps);
> +           ret = TRUE;
> +       }
> +       default:
> +           ret = gst_pad_query_default (pad, parent, query);
> +           break;
> +   }
> +
> +   return ret;
> +
> +}
> +
>     static void
>     gst_wavenc_init (GstWavEnc * wavenc)
>     {
> @@ -157,8 +201,15 @@ gst_wavenc_init (GstWavEnc * wavenc)
> 
>         wavenc->srcpad = gst_pad_new_from_static_template (&src_factory,
> "src");       gst_pad_use_fixed_caps (wavenc->srcpad);
> +   gst_pad_set_query_function (wavenc->srcpad,
> +           GST_DEBUG_FUNCPTR (gst_wavenc_src_query));
> +   gst_pad_set_event_function (wavenc->srcpad,
> +           GST_DEBUG_FUNCPTR (gst_wavenc_src_setcaps));
> +
> +   /*
>         gst_pad_set_caps (wavenc->srcpad,
>                 gst_static_pad_template_get_caps (&src_factory));
> +   */
>         gst_element_add_pad (GST_ELEMENT (wavenc), wavenc->srcpad);
>     }
> 
> @@ -377,6 +428,19 @@ gst_wavenc_push_header (GstWavEnc * wavenc)
>     }
> 
>     static gboolean
> +gst_wavenc_src_setcaps (GstPad *pad,   GstObject *parent, GstEvent
> *event ) +{
> +   GstCaps *caps;
> +   GstWavEnc * wavenc = GST_WAVENC (parent);
> +
> +   if (GST_EVENT_TYPE (event) == GST_EVENT_CAPS) {
> +         gst_event_parse_caps (event, &caps);
> +         GST_DEBUG_OBJECT (wavenc, "src caps are %" GST_PTR_FORMAT, caps);
> +   }
> +   return gst_pad_event_default (pad, parent, event);
> +}
> +
> +static gboolean
>     gst_wavenc_sink_setcaps (GstPad * pad, GstCaps * caps)
>     {
>         GstWavEnc *wavenc;
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