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mpegtspacketizer: Estimate clock skew and retimestamps buffers more precisly

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Apply the EPTLA algotithm to estimate clock skew.
Reusing code from  -good/gst/rtpmanager/rtpjitterbuffer.c
This commit is contained in:
Thibault Saunier 2012-02-23 14:46:09 -03:00 committed by Edward Hervey
parent 48a699812b
commit 6a8d2c45f6
3 changed files with 336 additions and 0 deletions
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3
gst/mpegtsdemux/mpegtsbase.c
View File

@ -1258,6 +1258,9 @@ query_upstream_latency (MpegTSBase * base)
GST_WARNING_OBJECT (base, "Failed to query upstream latency"); GST_WARNING_OBJECT (base, "Failed to query upstream latency");
gst_query_unref (query); gst_query_unref (query);
base->query_latency = TRUE; base->query_latency = TRUE;
/* Calculate clock skew for live streams only */
base->packetizer->calculate_skew = base->upstream_live;
} }
static inline GstFlowReturn static inline GstFlowReturn

314
gst/mpegtsdemux/mpegtspacketizer.c
View File

@ -28,6 +28,8 @@
* with newer GLib versions (>= 2.31.0) */ * with newer GLib versions (>= 2.31.0) */
#define GLIB_DISABLE_DEPRECATION_WARNINGS #define GLIB_DISABLE_DEPRECATION_WARNINGS
/* Skew calculation pameters */
#define MAX_TIME (2 * GST_SECOND)
#include "mpegtspacketizer.h" #include "mpegtspacketizer.h"
#include "gstmpegdesc.h" #include "gstmpegdesc.h"
@ -78,6 +80,9 @@ static gchar *convert_to_utf8 (const gchar * text, gint length, guint start,
static gchar *get_encoding (const gchar * text, guint * start_text, static gchar *get_encoding (const gchar * text, guint * start_text,
gboolean * is_multibyte); gboolean * is_multibyte);
static gchar *get_encoding_and_convert (const gchar * text, guint length); static gchar *get_encoding_and_convert (const gchar * text, guint length);
static GstClockTime calculate_skew (MpegTSPacketizer2 * packetizer,
guint32 pcrtime, GstClockTime time);
static void mpegts_packetizer_reset_skew (MpegTSPacketizer2 * packetizer);
#define CONTINUITY_UNSET 255 #define CONTINUITY_UNSET 255
#define MAX_CONTINUITY 15 #define MAX_CONTINUITY 15
@ -165,6 +170,8 @@ mpegts_packetizer_init (MpegTSPacketizer2 * packetizer)
packetizer->empty = TRUE; packetizer->empty = TRUE;
packetizer->streams = g_new0 (MpegTSPacketizerStream *, 8192); packetizer->streams = g_new0 (MpegTSPacketizerStream *, 8192);
packetizer->know_packet_size = FALSE; packetizer->know_packet_size = FALSE;
packetizer->calculate_skew = FALSE;
mpegts_packetizer_reset_skew (packetizer);
} }
static void static void
@ -262,6 +269,9 @@ mpegts_packetizer_parse_adaptation_field_control (MpegTSPacketizer2 *
/* PCR */ /* PCR */
if (afcflags & MPEGTS_AFC_PCR_FLAG) { if (afcflags & MPEGTS_AFC_PCR_FLAG) {
packet->pcr = mpegts_packetizer_compute_pcr (data); packet->pcr = mpegts_packetizer_compute_pcr (data);
if (packetizer->calculate_skew)
packet->pcr = calculate_skew (packetizer, packet->pcr,
GST_BUFFER_TIMESTAMP (packet->buffer));
*data += 6; *data += 6;
} }
@ -2736,3 +2746,307 @@ failed:
return g_strndup (text, length - start_text); return g_strndup (text, length - start_text);
} }
} }
/**
* mpegts_packetizer_reset_skew:
* @packetizer: an #MpegTSPacketizer2
*
* Reset the skew calculations in @packetizer.
*/
static void
mpegts_packetizer_reset_skew (MpegTSPacketizer2 * packetizer)
{
packetizer->base_time = GST_CLOCK_TIME_NONE;
packetizer->base_pcrtime = GST_CLOCK_TIME_NONE;
packetizer->last_pcrtime = GST_CLOCK_TIME_NONE;
packetizer->window_pos = 0;
packetizer->window_filling = TRUE;
packetizer->window_min = 0;
packetizer->skew = 0;
packetizer->prev_send_diff = GST_CLOCK_TIME_NONE;
packetizer->prev_out_time = GST_CLOCK_TIME_NONE;
GST_DEBUG ("reset skew correction");
}
static void
mpegts_packetizer_resync (MpegTSPacketizer2 * packetizer, GstClockTime time,
GstClockTime gstpcrtime, gboolean reset_skew)
{
packetizer->base_time = time;
packetizer->base_pcrtime = gstpcrtime;
packetizer->prev_out_time = GST_CLOCK_TIME_NONE;
packetizer->prev_send_diff = GST_CLOCK_TIME_NONE;
if (reset_skew) {
packetizer->window_filling = TRUE;
packetizer->window_pos = 0;
packetizer->window_min = 0;
packetizer->window_size = 0;
packetizer->skew = 0;
}
}
/* Code mostly copied from -good/gst/rtpmanager/rtpjitterbuffer.c */
/* For the clock skew we use a windowed low point averaging algorithm as can be
* found in Fober, Orlarey and Letz, 2005, "Real Time Clock Skew Estimation
* over Network Delays":
* http://www.grame.fr/Ressources/pub/TR-050601.pdf
* http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.102.1546
*
* The idea is that the jitter is composed of:
*
* J = N + n
*
* N : a constant network delay.
* n : random added noise. The noise is concentrated around 0
*
* In the receiver we can track the elapsed time at the sender with:
*
* send_diff(i) = (Tsi - Ts0);
*
* Tsi : The time at the sender at packet i
* Ts0 : The time at the sender at the first packet
*
* This is the difference between the RTP timestamp in the first received packet
* and the current packet.
*
* At the receiver we have to deal with the jitter introduced by the network.
*
* recv_diff(i) = (Tri - Tr0)
*
* Tri : The time at the receiver at packet i
* Tr0 : The time at the receiver at the first packet
*
* Both of these values contain a jitter Ji, a jitter for packet i, so we can
* write:
*
* recv_diff(i) = (Cri + D + ni) - (Cr0 + D + n0))
*
* Cri : The time of the clock at the receiver for packet i
* D + ni : The jitter when receiving packet i
*
* We see that the network delay is irrelevant here as we can elliminate D:
*
* recv_diff(i) = (Cri + ni) - (Cr0 + n0))
*
* The drift is now expressed as:
*
* Drift(i) = recv_diff(i) - send_diff(i);
*
* We now keep the W latest values of Drift and find the minimum (this is the
* one with the lowest network jitter and thus the one which is least affected
* by it). We average this lowest value to smooth out the resulting network skew.
*
* Both the window and the weighting used for averaging influence the accuracy
* of the drift estimation. Finding the correct parameters turns out to be a
* compromise between accuracy and inertia.
*
* We use a 2 second window or up to 512 data points, which is statistically big
* enough to catch spikes (FIXME, detect spikes).
* We also use a rather large weighting factor (125) to smoothly adapt. During
* startup, when filling the window, we use a parabolic weighting factor, the
* more the window is filled, the faster we move to the detected possible skew.
*
* Returns: @time adjusted with the clock skew.
*/
static GstClockTime
calculate_skew (MpegTSPacketizer2 * packetizer, guint32 pcrtime,
GstClockTime time)
{
guint64 send_diff, recv_diff;
gint64 delta;
gint64 old;
gint pos, i;
GstClockTime gstpcrtime, out_time;
guint64 slope;
gstpcrtime = PCRTIME_TO_GSTTIME (pcrtime);
/* keep track of the last extended pcrtime */
packetizer->last_pcrtime = gstpcrtime;
/* first time, lock on to time and gstpcrtime */
if (G_UNLIKELY (!GST_CLOCK_TIME_IS_VALID (packetizer->base_time))) {
packetizer->base_time = time;
packetizer->prev_out_time = GST_CLOCK_TIME_NONE;
GST_DEBUG ("Taking new base time %" GST_TIME_FORMAT, GST_TIME_ARGS (time));
}
if (G_UNLIKELY (!GST_CLOCK_TIME_IS_VALID (packetizer->base_pcrtime))) {
packetizer->base_pcrtime = gstpcrtime;
packetizer->prev_send_diff = -1;
GST_DEBUG ("Taking new base pcrtime %" GST_TIME_FORMAT,
GST_TIME_ARGS (gstpcrtime));
}
if (G_LIKELY (gstpcrtime >= packetizer->base_pcrtime))
send_diff = gstpcrtime - packetizer->base_pcrtime;
else if (GST_CLOCK_TIME_IS_VALID (time)) {
/* elapsed time at sender, timestamps can go backwards and thus be smaller
* than our base time, take a new base time in that case. */
GST_WARNING ("backward timestamps at server, taking new base time");
mpegts_packetizer_resync (packetizer, time, gstpcrtime, FALSE);
send_diff = 0;
} else {
GST_WARNING ("backward timestamps at server but no timestamps");
send_diff = 0;
/* at least try to get a new timestamp.. */
packetizer->base_time = -1;
}
GST_DEBUG ("gstpcr %" GST_TIME_FORMAT ", base %"
GST_TIME_FORMAT ", send_diff %" GST_TIME_FORMAT,
GST_TIME_ARGS (gstpcrtime), GST_TIME_ARGS (packetizer->base_pcrtime),
GST_TIME_ARGS (send_diff));
/* we don't have an arrival timestamp so we can't do skew detection. we
* should still apply a timestamp based on RTP timestamp and base_time */
if (!GST_CLOCK_TIME_IS_VALID (time)
|| !GST_CLOCK_TIME_IS_VALID (packetizer->base_time))
goto no_skew;
/* elapsed time at receiver, includes the jitter */
recv_diff = time - packetizer->base_time;
/* measure the diff */
delta = ((gint64) recv_diff) - ((gint64) send_diff);
/* measure the slope, this gives a rought estimate between the sender speed
* and the receiver speed. This should be approximately 8, higher values
* indicate a burst (especially when the connection starts) */
slope = recv_diff > 0 ? (send_diff * 8) / recv_diff : 8;
GST_DEBUG ("time %" GST_TIME_FORMAT ", base %" GST_TIME_FORMAT ", recv_diff %"
GST_TIME_FORMAT ", slope %" G_GUINT64_FORMAT, GST_TIME_ARGS (time),
GST_TIME_ARGS (packetizer->base_time), GST_TIME_ARGS (recv_diff), slope);
/* if the difference between the sender timeline and the receiver timeline
* changed too quickly we have to resync because the server likely restarted
* its timestamps. */
if (ABS (delta - packetizer->skew) > GST_SECOND) {
GST_WARNING ("delta - skew: %" GST_TIME_FORMAT " too big, reset skew",
GST_TIME_ARGS (delta - packetizer->skew));
mpegts_packetizer_resync (packetizer, time, gstpcrtime, TRUE);
send_diff = 0;
delta = 0;
}
pos = packetizer->window_pos;
if (G_UNLIKELY (packetizer->window_filling)) {
/* we are filling the window */
GST_DEBUG ("filling %d, delta %" G_GINT64_FORMAT, pos, delta);
packetizer->window[pos++] = delta;
/* calc the min delta we observed */
if (G_UNLIKELY (pos == 1 || delta < packetizer->window_min))
packetizer->window_min = delta;
if (G_UNLIKELY (send_diff >= MAX_TIME || pos >= MAX_WINDOW)) {
packetizer->window_size = pos;
/* window filled */
GST_DEBUG ("min %" G_GINT64_FORMAT, packetizer->window_min);
/* the skew is now the min */
packetizer->skew = packetizer->window_min;
packetizer->window_filling = FALSE;
} else {
gint perc_time, perc_window, perc;
/* figure out how much we filled the window, this depends on the amount of
* time we have or the max number of points we keep. */
perc_time = send_diff * 100 / MAX_TIME;
perc_window = pos * 100 / MAX_WINDOW;
perc = MAX (perc_time, perc_window);
/* make a parabolic function, the closer we get to the MAX, the more value
* we give to the scaling factor of the new value */
perc = perc * perc;
/* quickly go to the min value when we are filling up, slowly when we are
* just starting because we're not sure it's a good value yet. */
packetizer->skew =
(perc * packetizer->window_min + ((10000 -
perc) * packetizer->skew)) / 10000;
packetizer->window_size = pos + 1;
}
} else {
/* pick old value and store new value. We keep the previous value in order
* to quickly check if the min of the window changed */
old = packetizer->window[pos];
packetizer->window[pos++] = delta;
if (G_UNLIKELY (delta <= packetizer->window_min)) {
/* if the new value we inserted is smaller or equal to the current min,
* it becomes the new min */
packetizer->window_min = delta;
} else if (G_UNLIKELY (old == packetizer->window_min)) {
gint64 min = G_MAXINT64;
/* if we removed the old min, we have to find a new min */
for (i = 0; i < packetizer->window_size; i++) {
/* we found another value equal to the old min, we can stop searching now */
if (packetizer->window[i] == old) {
min = old;
break;
}
if (packetizer->window[i] < min)
min = packetizer->window[i];
}
packetizer->window_min = min;
}
/* average the min values */
packetizer->skew =
(packetizer->window_min + (124 * packetizer->skew)) / 125;
GST_DEBUG ("delta %" G_GINT64_FORMAT ", new min: %" G_GINT64_FORMAT, delta,
packetizer->window_min);
}
/* wrap around in the window */
if (G_UNLIKELY (pos >= packetizer->window_size))
pos = 0;
packetizer->window_pos = pos;
no_skew:
/* the output time is defined as the base timestamp plus the PCR time
* adjusted for the clock skew .*/
if (packetizer->base_time != -1) {
out_time = packetizer->base_time + send_diff;
/* skew can be negative and we don't want to make invalid timestamps */
if (packetizer->skew < 0 && out_time < -packetizer->skew) {
out_time = 0;
} else {
out_time += packetizer->skew;
}
/* check if timestamps are not going backwards, we can only check this if we
* have a previous out time and a previous send_diff */
if (G_LIKELY (packetizer->prev_out_time != -1
&& packetizer->prev_send_diff != -1)) {
/* now check for backwards timestamps */
if (G_UNLIKELY (
/* if the server timestamps went up and the out_time backwards */
(send_diff > packetizer->prev_send_diff
&& out_time < packetizer->prev_out_time) ||
/* if the server timestamps went backwards and the out_time forwards */
(send_diff < packetizer->prev_send_diff
&& out_time > packetizer->prev_out_time) ||
/* if the server timestamps did not change */
send_diff == packetizer->prev_send_diff)) {
GST_DEBUG ("backwards timestamps, using previous time");
out_time = GSTTIME_TO_MPEGTIME (out_time);
}
}
} else {
/* We simply use the pcrtime without applying any skew compensation */
out_time = pcrtime;
}
packetizer->prev_out_time = out_time;
packetizer->prev_send_diff = send_diff;
GST_DEBUG ("skew %" G_GINT64_FORMAT ", out %" GST_TIME_FORMAT,
packetizer->skew, GST_TIME_ARGS (out_time));
return out_time;
}

19
gst/mpegtsdemux/mpegtspacketizer.h
View File

@ -28,6 +28,8 @@
#include <gst/base/gstadapter.h> #include <gst/base/gstadapter.h>
#include <glib.h> #include <glib.h>
#include "gstmpegdefs.h"
#define MPEGTS_NORMAL_PACKETSIZE 188 #define MPEGTS_NORMAL_PACKETSIZE 188
#define MPEGTS_M2TS_PACKETSIZE 192 #define MPEGTS_M2TS_PACKETSIZE 192
#define MPEGTS_DVB_ASI_PACKETSIZE 204 #define MPEGTS_DVB_ASI_PACKETSIZE 204
@ -39,6 +41,8 @@
#define MPEGTS_AFC_PCR_FLAG 0x10 #define MPEGTS_AFC_PCR_FLAG 0x10
#define MPEGTS_AFC_OPCR_FLAG 0x08 #define MPEGTS_AFC_OPCR_FLAG 0x08
#define MAX_WINDOW 512
G_BEGIN_DECLS G_BEGIN_DECLS
#define GST_TYPE_MPEGTS_PACKETIZER \ #define GST_TYPE_MPEGTS_PACKETIZER \
@ -79,6 +83,21 @@ struct _MpegTSPacketizer2 {
/* current offset of the tip of the adapter */ /* current offset of the tip of the adapter */
guint64 offset; guint64 offset;
gboolean empty; gboolean empty;
/* clock skew calculation */
gboolean calculate_skew;
GstClockTime base_time;
GstClockTime base_pcrtime;
GstClockTime base_extrtp;
GstClockTime prev_out_time;
GstClockTime last_pcrtime;
gint64 window[MAX_WINDOW];
guint window_pos;
guint window_size;
gboolean window_filling;
gint64 window_min;
gint64 skew;
gint64 prev_send_diff;
}; };
struct _MpegTSPacketizer2Class { struct _MpegTSPacketizer2Class {