1、rtp协议头
2、rtp可以基于TCP或者UDP
其中基于TCP需要加4个字节的RTP标志
3、rtph264depay定义解析函数gst_rtp_h264_depay_process，通过RFC 3984文档实现。
static void
gst_rtp_h264_depay_class_init (GstRtpH264DepayClass * klass)
{
GObjectClass *gobject_class;
GstElementClass *gstelement_class;
GstRTPBaseDepayloadClass *gstrtpbasedepayload_class;
gobject_class = (GObjectClass *) klass;
gstelement_class = (GstElementClass *) klass;
gstrtpbasedepayload_class = (GstRTPBaseDepayloadClass *) klass;
gobject_class->finalize = gst_rtp_h264_depay_finalize;
gobject_class->set_property = gst_rtp_h264_depay_set_property;
gobject_class->get_property = gst_rtp_h264_depay_get_property;
/**
* GstRtpH264Depay:wait-for-keyframe:
*
* Wait for the next keyframe after packet loss,
* meaningful only when outputting access units
*
* Since: 1.20
*/
g_object_class_install_property (gobject_class, PROP_WAIT_FOR_KEYFRAME,
g_param_spec_boolean ("wait-for-keyframe", "Wait for Keyframe",
"Wait for the next keyframe after packet loss, meaningful only when "
"outputting access units",
DEFAULT_WAIT_FOR_KEYFRAME,
G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
/**
* GstRtpH264Depay:request-keyframe:
*
* Request new keyframe when packet loss is detected
*
* Since: 1.20
*/
g_object_class_install_property (gobject_class, PROP_REQUEST_KEYFRAME,
g_param_spec_boolean ("request-keyframe", "Request Keyframe",
"Request new keyframe when packet loss is detected",
DEFAULT_REQUEST_KEYFRAME,
G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
gst_element_class_add_static_pad_template (gstelement_class,
&gst_rtp_h264_depay_src_template);
gst_element_class_add_static_pad_template (gstelement_class,
&gst_rtp_h264_depay_sink_template);
gst_element_class_set_static_metadata (gstelement_class,
"RTP H264 depayloader", "Codec/Depayloader/Network/RTP",
"Extracts H264 video from RTP packets (RFC 3984)",
"Wim Taymans <wim.taymans@gmail.com>");
gstelement_class->change_state = gst_rtp_h264_depay_change_state;
gstrtpbasedepayload_class->process_rtp_packet = gst_rtp_h264_depay_process;
gstrtpbasedepayload_class->set_caps = gst_rtp_h264_depay_setcaps;
gstrtpbasedepayload_class->handle_event = gst_rtp_h264_depay_handle_event;
}4、gst_rtp_h264_depay_process的具体实现
static GstBuffer *
gst_rtp_h264_depay_process (GstRTPBaseDepayload * depayload, GstRTPBuffer * rtp)
{
GstRtpH264Depay *rtph264depay;
GstBuffer *outbuf = NULL;
guint8 nal_unit_type;
rtph264depay = GST_RTP_H264_DEPAY (depayload);
if (!rtph264depay->merge)
rtph264depay->waiting_for_keyframe = FALSE;
/* 是否是弃用数据 */
if (GST_BUFFER_IS_DISCONT (rtp->buffer)) {
gst_adapter_clear (rtph264depay->adapter);
rtph264depay->wait_start = TRUE;
rtph264depay->current_fu_type = 0;
rtph264depay->last_fu_seqnum = 0;
if (rtph264depay->merge && rtph264depay->wait_for_keyframe) {
rtph264depay->waiting_for_keyframe = TRUE;
}
if (rtph264depay->request_keyframe)
gst_pad_push_event (GST_RTP_BASE_DEPAYLOAD_SINKPAD (depayload),gst_video_event_new_upstream_force_key_unit (GST_CLOCK_TIME_NONE,TRUE, 0));
}
{
gint payload_len;
guint8 *payload;
guint header_len;
guint8 nal_ref_idc;
GstMapInfo map;
guint outsize, nalu_size;
GstClockTime timestamp;
gboolean marker;
timestamp = GST_BUFFER_PTS (rtp->buffer);
payload_len = gst_rtp_buffer_get_payload_len (rtp);
payload = gst_rtp_buffer_get_payload (rtp);
marker = gst_rtp_buffer_get_marker (rtp);
GST_DEBUG_OBJECT (rtph264depay, "receiving %d bytes", payload_len);
if (payload_len == 0)
goto empty_packet;
/* +---------------+
* |0|1|2|3|4|5|6|7|
* +-+-+-+-+-+-+-+-+
* |F|NRI| Type |
* +---------------+
*
* F must be 0.
*/
nal_ref_idc = (payload[0] & 0x60) >> 5;
nal_unit_type = payload[0] & 0x1f;
/* at least one byte header with type */
header_len = 1;
GST_DEBUG_OBJECT (rtph264depay, "NRI %d, Type %d %s", nal_ref_idc, nal_unit_type, marker ? "marker" : "");
/* If FU unit was being processed, but the current nal is of a different
* type. Assume that the remote payloader is buggy (didn't set the end bit
* when the FU ended) and send out what we gathered thusfar */
if (G_UNLIKELY (rtph264depay->current_fu_type != 0 && nal_unit_type != rtph264depay->current_fu_type))
gst_rtp_h264_finish_fragmentation_unit (rtph264depay);
switch (nal_unit_type) {
case 0:
case 30:
case 31:
/* undefined */
goto undefined_type;
case 25:
/* STAP-B Single-time aggregation packet 5.7.1 */
/* 2 byte extra header for DON */
header_len += 2;
/* fallthrough */
case 24:
{
/* strip headers */
payload += header_len;
payload_len -= header_len;
rtph264depay->wait_start = FALSE;
/* STAP-A Single-time aggregation packet 5.7.1 */
while (payload_len > 2) {
gboolean last = FALSE;
/* 1
* 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* | NALU Size |
* +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*/
nalu_size = (payload[0] << 8) | payload[1];
/* don't include nalu_size */
if (nalu_size > (payload_len - 2))
nalu_size = payload_len - 2;
outsize = nalu_size + sizeof (sync_bytes);
outbuf = gst_buffer_new_and_alloc (outsize);
gst_buffer_map (outbuf, &map, GST_MAP_WRITE);
if (rtph264depay->byte_stream) {
memcpy (map.data, sync_bytes, sizeof (sync_bytes));
} else {
map.data[0] = map.data[1] = 0;
map.data[2] = payload[0];
map.data[3] = payload[1];
}
/* strip NALU size */
payload += 2;
payload_len -= 2;
memcpy (map.data + sizeof (sync_bytes), payload, nalu_size);
gst_buffer_unmap (outbuf, &map);
gst_rtp_copy_video_meta (rtph264depay, outbuf, rtp->buffer);
if (payload_len - nalu_size <= 2)
last = TRUE;
gst_rtp_h264_depay_handle_nal (rtph264depay, outbuf, timestamp,
marker && last);
payload += nalu_size;
payload_len -= nalu_size;
}
break;
}
case 26:
/* MTAP16 Multi-time aggregation packet 5.7.2 */
// header_len = 5;
/* fallthrough, not implemented */
case 27:
/* MTAP24 Multi-time aggregation packet 5.7.2 */
// header_len = 6;
goto not_implemented;
break;
case 28:
case 29:
{
/* FU-A Fragmentation unit 5.8 */
/* FU-B Fragmentation unit 5.8 */
gboolean S, E;
/* +---------------+
* |0|1|2|3|4|5|6|7|
* +-+-+-+-+-+-+-+-+
* |S|E|R| Type |
* +---------------+
*
* R is reserved and always 0
*/
S = (payload[1] & 0x80) == 0x80;
E = (payload[1] & 0x40) == 0x40;
GST_DEBUG_OBJECT (rtph264depay, "S %d, E %d", S, E);
if (rtph264depay->wait_start && !S)
goto waiting_start;
if (S) {
/* NAL unit starts here */
guint8 nal_header;
/* If a new FU unit started, while still processing an older one.
* Assume that the remote payloader is buggy (doesn't set the end
* bit) and send out what we've gathered thusfar */
if (G_UNLIKELY (rtph264depay->current_fu_type != 0))
gst_rtp_h264_finish_fragmentation_unit (rtph264depay);
rtph264depay->current_fu_type = nal_unit_type;
rtph264depay->fu_timestamp = timestamp;
rtph264depay->last_fu_seqnum = gst_rtp_buffer_get_seq (rtp);
rtph264depay->wait_start = FALSE;
/* reconstruct NAL header */
nal_header = (payload[0] & 0xe0) | (payload[1] & 0x1f);
/* strip type header, keep FU header, we'll reuse it to reconstruct
* the NAL header. */
payload += 1;
payload_len -= 1;
nalu_size = payload_len;
outsize = nalu_size + sizeof (sync_bytes);
outbuf = gst_buffer_new_and_alloc (outsize);
gst_buffer_map (outbuf, &map, GST_MAP_WRITE);
memcpy (map.data + sizeof (sync_bytes), payload, nalu_size);
map.data[sizeof (sync_bytes)] = nal_header;
gst_buffer_unmap (outbuf, &map);
gst_rtp_copy_video_meta (rtph264depay, outbuf, rtp->buffer);
GST_DEBUG_OBJECT (rtph264depay, "queueing %d bytes", outsize);
/* and assemble in the adapter */
gst_adapter_push (rtph264depay->adapter, outbuf);
} else {
if (rtph264depay->current_fu_type == 0) {
/* previous FU packet missing start bit? */
GST_WARNING_OBJECT (rtph264depay, "missing FU start bit on an "
"earlier packet. Dropping.");
gst_adapter_clear (rtph264depay->adapter);
return NULL;
}
if (gst_rtp_buffer_compare_seqnum (rtph264depay->last_fu_seqnum,
gst_rtp_buffer_get_seq (rtp)) != 1) {
/* jump in sequence numbers within an FU is cause for discarding */
GST_WARNING_OBJECT (rtph264depay, "Jump in sequence numbers from "
"%u to %u within Fragmentation Unit. Data was lost, dropping "
"stored.", rtph264depay->last_fu_seqnum,
gst_rtp_buffer_get_seq (rtp));
gst_adapter_clear (rtph264depay->adapter);
return NULL;
}
rtph264depay->last_fu_seqnum = gst_rtp_buffer_get_seq (rtp);
/* strip off FU indicator and FU header bytes */
payload += 2;
payload_len -= 2;
outsize = payload_len;
outbuf = gst_buffer_new_and_alloc (outsize);
gst_buffer_fill (outbuf, 0, payload, outsize);
gst_rtp_copy_video_meta (rtph264depay, outbuf, rtp->buffer);
GST_DEBUG_OBJECT (rtph264depay, "queueing %d bytes", outsize);
/* and assemble in the adapter */
gst_adapter_push (rtph264depay->adapter, outbuf);
}
outbuf = NULL;
rtph264depay->fu_marker = marker;
/* if NAL unit ends, flush the adapter */
if (E)
gst_rtp_h264_finish_fragmentation_unit (rtph264depay);
break;
}
default:
{
rtph264depay->wait_start = FALSE;
/* 1-23 NAL unit Single NAL unit packet per H.264 5.6 */
/* the entire payload is the output buffer */
nalu_size = payload_len;
outsize = nalu_size + sizeof (sync_bytes);
outbuf = gst_buffer_new_and_alloc (outsize);
gst_buffer_map (outbuf, &map, GST_MAP_WRITE);
if (rtph264depay->byte_stream) {
memcpy (map.data, sync_bytes, sizeof (sync_bytes));
} else {
map.data[0] = map.data[1] = 0;
map.data[2] = nalu_size >> 8;
map.data[3] = nalu_size & 0xff;
}
memcpy (map.data + sizeof (sync_bytes), payload, nalu_size);
gst_buffer_unmap (outbuf, &map);
gst_rtp_copy_video_meta (rtph264depay, outbuf, rtp->buffer);
gst_rtp_h264_depay_handle_nal (rtph264depay, outbuf, timestamp, marker);
break;
}
}
}
return NULL;
/* ERRORS */
empty_packet:
{
GST_DEBUG_OBJECT (rtph264depay, "empty packet");
return NULL;
}
undefined_type:
{
GST_ELEMENT_WARNING (rtph264depay, STREAM, DECODE,
(NULL), ("Undefined packet type"));
return NULL;
}
waiting_start:
{
GST_DEBUG_OBJECT (rtph264depay, "waiting for start");
return NULL;
}
not_implemented:
{
GST_ELEMENT_ERROR (rtph264depay, STREAM, FORMAT,
(NULL), ("NAL unit type %d not supported yet", nal_unit_type));
return NULL;
}
}
