[FFmpeg-cvslog] v4l2: allow to convert monotonic timestamps.
Nicolas George
git at videolan.org
Wed Apr 4 15:23:30 CEST 2012
ffmpeg | branch: master | Nicolas George <nicolas.george at normalesup.org> | Sat Mar 3 15:56:11 2012 +0100| [12292f35a3affe1265d63acba98f651cf82ae233] | committer: Nicolas George
v4l2: allow to convert monotonic timestamps.
> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=12292f35a3affe1265d63acba98f651cf82ae233
---
configure | 2 +
doc/indevs.texi | 7 ++++
libavdevice/Makefile | 2 +-
libavdevice/v4l2.c | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 104 insertions(+), 1 deletions(-)
diff --git a/configure b/configure
index 1eb8e92..1b75390 100755
--- a/configure
+++ b/configure
@@ -1157,6 +1157,7 @@ HAVE_LIST="
attribute_may_alias
attribute_packed
cbrtf
+ clock_gettime
closesocket
cmov
dcbzl
@@ -3048,6 +3049,7 @@ fi
# Solaris has nanosleep in -lrt, OpenSolaris no longer needs that
check_func nanosleep || { check_func nanosleep -lrt && add_extralibs -lrt; }
+check_func clock_gettime || { check_func clock_gettime -lrt && add_extralibs -lrt; }
check_func fcntl
check_func fork
check_func getaddrinfo $network_extralibs
diff --git a/doc/indevs.texi b/doc/indevs.texi
index f41c1cb..e699e11 100644
--- a/doc/indevs.texi
+++ b/doc/indevs.texi
@@ -520,6 +520,13 @@ supported using @command{-list_formats all} for Video4Linux2 devices.
Some usage examples of the video4linux2 devices with ffmpeg and ffplay:
+The time base for the timestamps is 1 microsecond. Depending on the kernel
+version and configuration, the timestamps may be derived from the real time
+clock (origin at the Unix Epoch) or the monotonic clock (origin usually at
+boot time, unaffected by NTP or manual changes to the clock). The
+ at option{-timestamps abs} or @option{-ts abs} option can be used to force
+conversion into the real time clock.
+
Note that if FFmpeg is build with v4l-utils support ("--enable-libv4l2"
option), it will always be used.
@example
diff --git a/libavdevice/Makefile b/libavdevice/Makefile
index d7806ea..7f0c1d3 100644
--- a/libavdevice/Makefile
+++ b/libavdevice/Makefile
@@ -28,7 +28,7 @@ OBJS-$(CONFIG_PULSE_INDEV) += pulse.o
OBJS-$(CONFIG_SDL_OUTDEV) += sdl.o
OBJS-$(CONFIG_SNDIO_INDEV) += sndio_common.o sndio_dec.o
OBJS-$(CONFIG_SNDIO_OUTDEV) += sndio_common.o sndio_enc.o
-OBJS-$(CONFIG_V4L2_INDEV) += v4l2.o
+OBJS-$(CONFIG_V4L2_INDEV) += v4l2.o timefilter.o
OBJS-$(CONFIG_V4L_INDEV) += v4l.o
OBJS-$(CONFIG_VFWCAP_INDEV) += vfwcap.o
OBJS-$(CONFIG_X11_GRAB_DEVICE_INDEV) += x11grab.o
diff --git a/libavdevice/v4l2.c b/libavdevice/v4l2.c
index 642df1d..cecc18d 100644
--- a/libavdevice/v4l2.c
+++ b/libavdevice/v4l2.c
@@ -51,6 +51,7 @@
#include "libavutil/log.h"
#include "libavutil/opt.h"
#include "avdevice.h"
+#include "timefilter.h"
#include "libavutil/parseutils.h"
#include "libavutil/pixdesc.h"
#include "libavutil/avstring.h"
@@ -73,6 +74,28 @@ static const int desired_video_buffers = 256;
#define V4L_RAWFORMATS 1
#define V4L_COMPFORMATS 2
+/**
+ * Return timestamps to the user exactly as returned by the kernel
+ */
+#define V4L_TS_DEFAULT 0
+/**
+ * Autodetect the kind of timestamps returned by the kernel and convert to
+ * absolute (wall clock) timestamps.
+ */
+#define V4L_TS_ABS 1
+/**
+ * Assume kernel timestamps are from the monotonic clock and convert to
+ * absolute timestamps.
+ */
+#define V4L_TS_MONO2ABS 2
+
+/**
+ * Once the kind of timestamps returned by the kernel have been detected,
+ * the value of the timefilter (NULL or not) determines whether a conversion
+ * takes place.
+ */
+#define V4L_TS_CONVERT_READY V4L_TS_DEFAULT
+
struct video_data {
AVClass *class;
int fd;
@@ -81,6 +104,9 @@ struct video_data {
int frame_size;
int interlaced;
int top_field_first;
+ int ts_mode;
+ TimeFilter *timefilter;
+ int64_t last_time_m;
int buffers;
void **buf_start;
@@ -455,6 +481,66 @@ static void mmap_release_buffer(AVPacket *pkt)
pkt->size = 0;
}
+#if HAVE_CLOCK_GETTIME && defined(CLOCK_MONOTONIC)
+static int64_t av_gettime_monotonic(void)
+{
+ struct timespec tv;
+
+ clock_gettime(CLOCK_MONOTONIC, &tv);
+ return (int64_t)tv.tv_sec * 1000000 + tv.tv_nsec / 1000;
+}
+#endif
+
+static int init_convert_timestamp(AVFormatContext *ctx, int64_t ts)
+{
+ struct video_data *s = ctx->priv_data;
+ int64_t now;
+
+ now = av_gettime();
+ if (s->ts_mode == V4L_TS_ABS &&
+ ts <= now + 1 * AV_TIME_BASE && ts >= now - 10 * AV_TIME_BASE) {
+ av_log(ctx, AV_LOG_INFO, "Detected absolute timestamps\n");
+ s->ts_mode = V4L_TS_CONVERT_READY;
+ return 0;
+ }
+#if HAVE_CLOCK_GETTIME && defined(CLOCK_MONOTONIC)
+ now = av_gettime_monotonic();
+ if (s->ts_mode == V4L_TS_MONO2ABS ||
+ (ts <= now + 1 * AV_TIME_BASE && ts >= now - 10 * AV_TIME_BASE)) {
+ int64_t period = av_rescale_q(1, ctx->streams[0]->codec->time_base,
+ AV_TIME_BASE_Q);
+ av_log(ctx, AV_LOG_INFO, "Detected monotonic timestamps, converting\n");
+ /* microseconds instead of seconds, MHz instead of Hz */
+ s->timefilter = ff_timefilter_new(1, period, 1.0E-6);
+ s->ts_mode = V4L_TS_CONVERT_READY;
+ return 0;
+ }
+#endif
+ av_log(ctx, AV_LOG_ERROR, "Unknown timestamps\n");
+ return AVERROR(EIO);
+}
+
+static int convert_timestamp(AVFormatContext *ctx, int64_t *ts)
+{
+ struct video_data *s = ctx->priv_data;
+
+ if (s->ts_mode) {
+ int r = init_convert_timestamp(ctx, *ts);
+ if (r < 0)
+ return r;
+ }
+#if HAVE_CLOCK_GETTIME && defined(CLOCK_MONOTONIC)
+ if (s->timefilter) {
+ int64_t nowa = av_gettime();
+ int64_t nowm = av_gettime_monotonic();
+ ff_timefilter_update(s->timefilter, nowa, nowm - s->last_time_m);
+ s->last_time_m = nowm;
+ *ts = ff_timefilter_eval(s->timefilter, *ts - nowm);
+ }
+#endif
+ return 0;
+}
+
static int mmap_read_frame(AVFormatContext *ctx, AVPacket *pkt)
{
struct video_data *s = ctx->priv_data;
@@ -490,6 +576,9 @@ static int mmap_read_frame(AVFormatContext *ctx, AVPacket *pkt)
pkt->data= s->buf_start[buf.index];
pkt->size = buf.bytesused;
pkt->pts = buf.timestamp.tv_sec * INT64_C(1000000) + buf.timestamp.tv_usec;
+ res = convert_timestamp(ctx, &pkt->pts);
+ if (res < 0)
+ return res;
pkt->destruct = mmap_release_buffer;
buf_descriptor = av_malloc(sizeof(struct buff_data));
if (buf_descriptor == NULL) {
@@ -847,6 +936,11 @@ static const AVOption options[] = {
{ "all", "Show all available formats", OFFSET(list_format), AV_OPT_TYPE_CONST, {.dbl = V4L_ALLFORMATS }, 0, INT_MAX, DEC, "list_formats" },
{ "raw", "Show only non-compressed formats", OFFSET(list_format), AV_OPT_TYPE_CONST, {.dbl = V4L_RAWFORMATS }, 0, INT_MAX, DEC, "list_formats" },
{ "compressed", "Show only compressed formats", OFFSET(list_format), AV_OPT_TYPE_CONST, {.dbl = V4L_COMPFORMATS }, 0, INT_MAX, DEC, "list_formats" },
+ { "timestamps", "Kind of timestamps for grabbed frames", OFFSET(ts_mode), AV_OPT_TYPE_INT, {.dbl = 0 }, 0, 2, DEC, "timestamps" },
+ { "default", "Use timestamps from the kernel", OFFSET(ts_mode), AV_OPT_TYPE_CONST, {.dbl = V4L_TS_DEFAULT }, 0, 2, DEC, "timestamps" },
+ { "abs", "Use absolute timestamps (wall clock)", OFFSET(ts_mode), AV_OPT_TYPE_CONST, {.dbl = V4L_TS_ABS }, 0, 2, DEC, "timestamps" },
+ { "mono2abs", "Force conversion from monotonic to absolute timestamps", OFFSET(ts_mode), AV_OPT_TYPE_CONST, {.dbl = V4L_TS_MONO2ABS }, 0, 2, DEC, "timestamps" },
+ { "ts", "Kind of timestamps for grabbed frames", OFFSET(ts_mode), AV_OPT_TYPE_INT, {.dbl = 0 }, 0, 2, DEC, "timestamps" },
{ NULL },
};
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