Commit 38a28fda authored by Wim Taymans's avatar Wim Taymans
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ext/theora/: Document and partially implement an algorithm for doing reverse...

ext/theora/: Document and partially implement an algorithm for doing reverse playback of theora video.

Original commit message from CVS:
* ext/theora/gsttheoradec.h:
* ext/theora/theoradec.c: (gst_theora_dec_init),
(theora_dec_sink_event), (theora_dec_chain_forward),
(theora_dec_flush_decode), (theora_dec_chain_reverse),
(theora_dec_chain):
Document and partially implement an algorithm for doing reverse playback
of theora video.
parent f4010367
2006-11-02 Wim Taymans <wim@fluendo.com>
* ext/theora/gsttheoradec.h:
* ext/theora/theoradec.c: (gst_theora_dec_init),
(theora_dec_sink_event), (theora_dec_chain_forward),
(theora_dec_flush_decode), (theora_dec_chain_reverse),
(theora_dec_chain):
Document and partially implement an algorithm for doing reverse playback
of theora video.
2006-11-02 Tim-Philipp Müller <tim at centricular dot net>
 
Patch by: Sergey Scobich <sergey.scobich at gmail com>
......@@ -74,7 +74,13 @@ struct _GstTheoraDec
gboolean crop;
/* list of buffers that need timestamps */
GList *queued;
/* list of raw output buffers */
GList *output;
/* gather/decode queues for reverse playback */
GList *gather;
GList *decode;
/* segment info */ /* with STREAM_LOCK */
GstSegment segment;
......
......@@ -163,6 +163,8 @@ gst_theora_dec_init (GstTheoraDec * dec, GstTheoraDecClass * g_class)
gst_element_add_pad (GST_ELEMENT (dec), dec->srcpad);
dec->crop = THEORA_DEF_CROP;
dec->gather = NULL;
dec->decode = NULL;
dec->queued = NULL;
}
......@@ -681,9 +683,6 @@ theora_dec_sink_event (GstPad * pad, GstEvent * event)
if (format != GST_FORMAT_TIME)
goto newseg_wrong_format;
if (rate <= 0.0)
goto newseg_wrong_rate;
/* now configure the values */
gst_segment_set_newsegment_full (&dec->segment, update,
rate, arate, format, start, stop, time);
......@@ -708,12 +707,6 @@ newseg_wrong_format:
gst_event_unref (event);
goto done;
}
newseg_wrong_rate:
{
GST_DEBUG_OBJECT (dec, "negative rates not supported yet");
gst_event_unref (event);
goto done;
}
}
static GstFlowReturn
......@@ -1150,16 +1143,13 @@ no_buffer:
}
static GstFlowReturn
theora_dec_chain (GstPad * pad, GstBuffer * buf)
theora_dec_chain_forward (GstTheoraDec * dec, gboolean discont, GstBuffer * buf)
{
GstTheoraDec *dec;
ogg_packet packet;
GstFlowReturn result = GST_FLOW_OK;
dec = GST_THEORA_DEC (gst_pad_get_parent (pad));
/* resync on DISCONT */
if (G_UNLIKELY (GST_BUFFER_FLAG_IS_SET (buf, GST_BUFFER_FLAG_DISCONT))) {
if (G_UNLIKELY (discont)) {
GST_DEBUG_OBJECT (dec, "received DISCONT buffer");
dec->need_keyframe = TRUE;
dec->last_timestamp = -1;
......@@ -1209,13 +1199,173 @@ done:
/* interpolate granule pos */
dec->granulepos = _inc_granulepos (dec, dec->granulepos);
gst_object_unref (dec);
gst_buffer_unref (buf);
return result;
}
/* For reverse playback we use a technique that can be used for
* any keyframe based video codec.
*
* Input:
* Buffer decoding order: 7 8 9 4 5 6 1 2 3 EOS
* Keyframe flag: K K
* Discont flag: D D D
*
* - Each Discont marks a discont in the decoding order.
* - The keyframes mark where we can start decoding.
*
* First we prepend incomming buffers to the gather queue, whenever we receive
* a discont, we flush out the gather queue.
*
* The above data will be accumulated in the gather queue like this:
*
* gather queue: 9 8 7
* D
*
* Whe buffer 4 is received (with a DISCONT), we flush the gather queue like
* this:
*
* while (gather)
* take head of queue and prepend to decode queue.
* if we copied a keyframe, decode the decode queue.
*
* After we flushed the gather queue, we add 4 to the (now empty) gather queue.
* We get the following situation:
*
* gather queue: 4
* decode queue: 7 8 9
*
* After we received 5 (Keyframe) and 6:
*
* gather queue: 6 5 4
* decode queue: 7 8 9
*
* When we receive 1 (DISCONT) which triggers a flush of the gather queue:
*
* Copy head of the gather queue (6) to decode queue:
*
* gather queue: 5 4
* decode queue: 6 7 8 9
*
* Copy head of the gather queue (5) to decode queue. This is a keyframe so we
* can start decoding.
*
* gather queue: 4
* decode queue: 5 6 7 8 9
*
* Decode frames in decode queue, store raw decoded data in output queue, we
* can take the head of the decode queue and prepend the decoded result in the
* output queue:
*
* gather queue: 4
* decode queue:
* output queue: 9 8 7 6 5
*
* Now output all the frames in the output queue, picking a frame from the
* head of the queue.
*
* Copy head of the gather queue (4) to decode queue, we flushed the gather
* queue an can now store input buffer in the gather queue:
*
* gather queue: 1
* decode queue: 4
*
* When we receive EOS, the queue looks like:
*
* gather queue: 3 2 1
* decode queue: 4
*
* Fill decode queue, first keyframe we copy is 2:
*
* gather queue: 1
* decode queue: 2 3 4
*
* Decoded output:
*
* gather queue: 1
* decode queue:
* output queue: 4 3 2
*
* Leftover buffer 1 cannot be decoded and must be discarded.
*/
static GstFlowReturn
theora_dec_flush_decode (GstTheoraDec * dec)
{
GstFlowReturn res = GST_FLOW_OK;
while (dec->decode) {
GstBuffer *buf = GST_BUFFER_CAST (dec->decode->data);
/* FIXME, decode buffer, prepend to output queue */
gst_buffer_unref (buf);
dec->decode = g_list_delete_link (dec->decode, dec->decode);
}
while (dec->queued) {
GstBuffer *buf = GST_BUFFER_CAST (dec->queued->data);
/* iterate ouput queue an push downstream */
res = gst_pad_push (dec->srcpad, buf);
dec->queued = g_list_delete_link (dec->queued, dec->queued);
}
return res;
}
static GstFlowReturn
theora_dec_chain_reverse (GstTheoraDec * dec, gboolean discont, GstBuffer * buf)
{
GstFlowReturn res = GST_FLOW_OK;
/* if we have a discont, move buffers to the decode list */
if (discont) {
while (dec->gather) {
GstBuffer *buf;
guint8 *data;
buf = GST_BUFFER_CAST (dec->gather->data);
/* remove from the gather list */
dec->gather = g_list_delete_link (dec->gather, dec->gather);
/* copy to decode queue */
dec->decode = g_list_prepend (dec->decode, buf);
/* if we copied a keyframe, flush and decode the decode queue */
data = GST_BUFFER_DATA (buf);
if ((data[0] & 0x40) == 0)
res = theora_dec_flush_decode (dec);
}
}
/* add buffer to gather queue */
dec->gather = g_list_prepend (dec->gather, buf);
return res;
}
static GstFlowReturn
theora_dec_chain (GstPad * pad, GstBuffer * buf)
{
GstTheoraDec *dec;
GstFlowReturn res;
gboolean discont;
dec = GST_THEORA_DEC (gst_pad_get_parent (pad));
/* peel of DISCONT flag */
discont = GST_BUFFER_FLAG_IS_SET (buf, GST_BUFFER_FLAG_DISCONT);
if (dec->segment.rate > 0.0)
res = theora_dec_chain_forward (dec, discont, buf);
else
res = theora_dec_chain_reverse (dec, discont, buf);
gst_object_unref (dec);
return res;
}
static GstStateChangeReturn
theora_dec_change_state (GstElement * element, GstStateChange transition)
{
......
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