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140 lines
3 KiB
Text
140 lines
3 KiB
Text
some random ramblings about the event system:
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Possible candidates for events
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------------------------------
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- QoS
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- EOS
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- Seek
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- caps nego??
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- bufferpool get??
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- ...
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Assumptions for events
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----------------------
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- They are tied to a pad.
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- get rid of gst_pad_set_*_function (except for the chain/get ones)
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- occur async to dataflow. (need locking?)
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- fixed set of events only for core features. (elements cannot abuse
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events for doing dataflow)
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Questions
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---------
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limit the valid directions an event can travel in? ie. Can EOS only
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travel downstream (left to right)?
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eg. Seek travels upstream, but it makes sense to also make it travel
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downstream (the case of a disksink, where we overwrite the header)
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Setting an event function
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-------------------------
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void gst_pad_set_event_function (GstPad *pad, gint event_mask,
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GstEventFunction *function);
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event masks:
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typedef enum {
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GST_EVENT_EOS = (1 << 0),
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GST_EVENT_QOS = (1 << 1),
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GST_EVENT_SEEK = (1 << 2),
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GST_EVENT_CAPS = (1 << 3),
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} GstEventType;
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Event structure
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---------------
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typedef struct {
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GstEventType type;
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GstEventMinorType minor;
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guint64 timestamp; /* also sequence number ?? */
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union {
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/* EOS stuff */
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/* QoS stuff */
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/* Seek stuff */
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GstSeekType type; /* time, bytes, ... */
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gint64 offset;
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gint64 lenth;
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/* Caps stuff */
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GstCaps *caps;
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} data;
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} GstEvent;
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typedef enum {
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GST_EVENT_MINOR_NONE,
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/* EOS stuff */
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/* QoS stuff */
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/* Seek stuff */
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GST_EVENT_MINOR_OFFSET,
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GST_EVENT_MINOR_TIME,
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/* caps nego stuff */
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GST_EVENT_MINOR_CAPS_TRY,
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GST_EVENT_MINOR_CAPS_START,
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GST_EVENT_MINOR_CAPS_FINAL,
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} GstEventMinorType;
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Receiving events
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----------------
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a sample GstEventFunction, the event functions returns TRUE if the event is handled,
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FALSE otherwise.
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gboolean
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gst_anelement_handle_event (GstPad *pad, GstEvent *event)
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{
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if (event->type == GST_EVENT_EOS) {
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/* do something */
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return TRUE;
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}
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else if (event->type == GST_EVENT_CAPS) {
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if (event->minor == GST_EVENT_CAPS_TRY) {
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/* try using this caps structure */
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return TRUE; /* return FALSE to proxy ???*/
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}
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}
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return FALSE;
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}
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Default event handler for pads
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------------------------------
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gboolean
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gst_pad_handle_event (GstPad *pad, GstEvent *event)
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{
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GstElement *element;
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GList *pads;
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GstPad *srcpad;
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gboolean result = TRUE;
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GstPadDirection dir = GST_PAD_DIRECTION (pad);
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g_return_val_if_fail (pad != NULL, FALSE);
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g_return_val_if_fail (GST_IS_REAL_PAD(pad), FALSE); // NOTE the restriction
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element = GST_ELEMENT (gst_object_get_parent (GST_OBJECT (pad)));
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/* send out the events to all pad with opposite direction */
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pads = gst_element_get_pad_list(element);
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while (pads) {
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otherpad = GST_PAD(pads->data);
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pads = g_list_next(pads);
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if (gst_pad_get_direction(otherpad) != dir) {
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result &= gst_pad_send_event (GST_REAL_PAD(otherpad), event);
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}
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}
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/* result is combined result of all handlers? */
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return result;
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}
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