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authorThibault Saunier <thibault.saunier@collabora.com>2012-02-23 17:46:09 (GMT)
committerEdward Hervey <edward.hervey@collabora.co.uk>2012-02-24 09:57:09 (GMT)
commit6a8d2c45f6d0b0d8d2ef25a639ff35787af4544e (patch)
treec9045aaab00868c7f50bf8d328eaa34f8a6f004a
parent48a699812b5cb25d712d737740e9cf64147c1eac (diff)
mpegtspacketizer: Estimate clock skew and retimestamps buffers more precisly
Apply the EPTLA algotithm to estimate clock skew. Reusing code from -good/gst/rtpmanager/rtpjitterbuffer.c
-rw-r--r--gst/mpegtsdemux/mpegtsbase.c3
-rw-r--r--gst/mpegtsdemux/mpegtspacketizer.c314
-rw-r--r--gst/mpegtsdemux/mpegtspacketizer.h19
3 files changed, 336 insertions, 0 deletions
diff --git a/gst/mpegtsdemux/mpegtsbase.c b/gst/mpegtsdemux/mpegtsbase.c
index 2b480c0..193e84a 100644
--- a/gst/mpegtsdemux/mpegtsbase.c
+++ b/gst/mpegtsdemux/mpegtsbase.c
@@ -1258,6 +1258,9 @@ query_upstream_latency (MpegTSBase * base)
GST_WARNING_OBJECT (base, "Failed to query upstream latency");
gst_query_unref (query);
base->query_latency = TRUE;
+
+ /* Calculate clock skew for live streams only */
+ base->packetizer->calculate_skew = base->upstream_live;
}
static inline GstFlowReturn
diff --git a/gst/mpegtsdemux/mpegtspacketizer.c b/gst/mpegtsdemux/mpegtspacketizer.c
index 85eac76..a7ce40f 100644
--- a/gst/mpegtsdemux/mpegtspacketizer.c
+++ b/gst/mpegtsdemux/mpegtspacketizer.c
@@ -28,6 +28,8 @@
* with newer GLib versions (>= 2.31.0) */
#define GLIB_DISABLE_DEPRECATION_WARNINGS
+/* Skew calculation pameters */
+#define MAX_TIME (2 * GST_SECOND)
#include "mpegtspacketizer.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,
gboolean * is_multibyte);
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 MAX_CONTINUITY 15
@@ -165,6 +170,8 @@ mpegts_packetizer_init (MpegTSPacketizer2 * packetizer)
packetizer->empty = TRUE;
packetizer->streams = g_new0 (MpegTSPacketizerStream *, 8192);
packetizer->know_packet_size = FALSE;
+ packetizer->calculate_skew = FALSE;
+ mpegts_packetizer_reset_skew (packetizer);
}
static void
@@ -262,6 +269,9 @@ mpegts_packetizer_parse_adaptation_field_control (MpegTSPacketizer2 *
/* PCR */
if (afcflags & MPEGTS_AFC_PCR_FLAG) {
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;
}
@@ -2736,3 +2746,307 @@ failed:
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;
+}
diff --git a/gst/mpegtsdemux/mpegtspacketizer.h b/gst/mpegtsdemux/mpegtspacketizer.h
index 8328625..84da5f6 100644
--- a/gst/mpegtsdemux/mpegtspacketizer.h
+++ b/gst/mpegtsdemux/mpegtspacketizer.h
@@ -28,6 +28,8 @@
#include <gst/base/gstadapter.h>
#include <glib.h>
+#include "gstmpegdefs.h"
+
#define MPEGTS_NORMAL_PACKETSIZE 188
#define MPEGTS_M2TS_PACKETSIZE 192
#define MPEGTS_DVB_ASI_PACKETSIZE 204
@@ -39,6 +41,8 @@
#define MPEGTS_AFC_PCR_FLAG 0x10
#define MPEGTS_AFC_OPCR_FLAG 0x08
+#define MAX_WINDOW 512
+
G_BEGIN_DECLS
#define GST_TYPE_MPEGTS_PACKETIZER \
@@ -79,6 +83,21 @@ struct _MpegTSPacketizer2 {
/* current offset of the tip of the adapter */
guint64 offset;
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 {