[FFmpeg-devel] [PATCH v3 1/1] avformat/demux: Add durationprobesize AVOption
Nicolas Gaullier
nicolas.gaullier at cji.paris
Mon Mar 11 17:57:19 EET 2024
Yet another probesize used to get the durations when
estimate_timings_from_pts is required. It is aimed at users interested
in better durations probing for itself, or because using
avformat_find_stream_info indirectly and requiring exact values: for
concatdec for example, especially if streamcopying above it.
The current code is a performance trade-off that can fail to get video
stream durations in a scenario with high bitrates and buffering for
files ending cleanly (as opposed to live captures): the physical gap
between the last video packet and the last audio packet is very high in
such a case.
Default behaviour is unchanged: 250k up to 250k << 6 (step by step).
Setting this new option has two effects:
- override the maximum probesize (currently 250k << 6)
- reduce the number of steps to 1 instead of 6, this is to avoid
detecting the audio "too early" and failing to reach a video packet.
Even if a single audio stream duration is found but not the other
audio/video stream durations, there will be a retry, so at the end the
full user-overriden probesize will be used as expected by the user.
Signed-off-by: Nicolas Gaullier <nicolas.gaullier at cji.paris>
---
doc/APIchanges | 3 +++
doc/formats.texi | 16 +++++++++++++++-
libavformat/avformat.h | 12 ++++++++++++
libavformat/demux.c | 13 ++++++++-----
libavformat/options_table.h | 1 +
libavformat/version.h | 2 +-
6 files changed, 40 insertions(+), 7 deletions(-)
diff --git a/doc/APIchanges b/doc/APIchanges
index cf58c8c5f0..c97acf60d1 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -2,6 +2,9 @@ The last version increases of all libraries were on 2024-03-07
API changes, most recent first:
+2024-03-11 - xxxxxxxxxx - lavf 61.1.100 - avformat.h
+ Add AVFormatContext.duration_probesize
+
2024-03-08 - xxxxxxxxxx - lavc 61.1.100 - avcodec.h
Add AVCodecContext.[nb_]side_data_prefer_packet.
diff --git a/doc/formats.texi b/doc/formats.texi
index 69fc1457a4..9cada03a6e 100644
--- a/doc/formats.texi
+++ b/doc/formats.texi
@@ -225,9 +225,23 @@ Specifies the maximum number of streams. This can be used to reject files that
would require too many resources due to a large number of streams.
@item skip_estimate_duration_from_pts @var{bool} (@emph{input})
-Skip estimation of input duration when calculated using PTS.
+Skip estimation of input duration if it requires an additional probing for pts at end of file.
At present, applicable for MPEG-PS and MPEG-TS.
+ at item durationprobesize @var{integer} (@emph{input})
+Set probing size for input duration estimation when it actually requires an additional probing
+for pts at end of file.
+At present, applicable for MPEG-PS and MPEG-TS.
+It is aimed at users interested in better durations probing for itself, or indirectly
+for specific use cases like using the concat demuxer.
+Files with high bitrates and ending cleanly (as opposed to live captures), can lead
+to a large physical gap between the last video packet and the last audio packet,
+so many bytes have to be read in order to get a video stream duration.
+Setting this value has a performance impact even for small files because the probing size is fixed.
+Default behaviour is a trade-off, largely adaptive: the probing size may range from
+250K up to 16M, but it is not extended to get streams durations at all costs.
+Must be an integer not lesser than 1, or 0 for default behaviour.
+
@item strict, f_strict @var{integer} (@emph{input/output})
Specify how strictly to follow the standards. @code{f_strict} is deprecated and
should be used only via the @command{ffmpeg} tool.
diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index de40397676..9042a62b70 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -1667,6 +1667,8 @@ typedef struct AVFormatContext {
* Skip duration calcuation in estimate_timings_from_pts.
* - encoding: unused
* - decoding: set by user
+ *
+ * @sa duration_probesize
*/
int skip_estimate_duration_from_pts;
@@ -1870,6 +1872,16 @@ typedef struct AVFormatContext {
* @return 0 on success, a negative AVERROR code on failure
*/
int (*io_close2)(struct AVFormatContext *s, AVIOContext *pb);
+
+ /**
+ * Maximum number of bytes read from input in order to determine stream durations
+ * when using estimate_timings_from_pts in avformat_find_stream_info().
+ * Demuxing only, set by the caller before avformat_find_stream_info().
+ * Can be set to 0 to let avformat choose using a heuristic.
+ *
+ * @sa skip_estimate_duration_from_pts
+ */
+ int64_t duration_probesize;
} AVFormatContext;
/**
diff --git a/libavformat/demux.c b/libavformat/demux.c
index 4c50eb5568..68b0c51720 100644
--- a/libavformat/demux.c
+++ b/libavformat/demux.c
@@ -1817,8 +1817,9 @@ static void estimate_timings_from_bit_rate(AVFormatContext *ic)
"Estimating duration from bitrate, this may be inaccurate\n");
}
-#define DURATION_MAX_READ_SIZE 250000LL
-#define DURATION_MAX_RETRY 6
+#define DURATION_MAX_READ_SIZE_DEFAULT 250000LL
+#define DURATION_MAX_RETRY_DEFAULT 6
+#define DURATION_MAX_RETRY_USER 1
/* only usable for MPEG-PS streams */
static void estimate_timings_from_pts(AVFormatContext *ic, int64_t old_offset)
@@ -1826,6 +1827,8 @@ static void estimate_timings_from_pts(AVFormatContext *ic, int64_t old_offset)
FFFormatContext *const si = ffformatcontext(ic);
AVPacket *const pkt = si->pkt;
int num, den, read_size, ret;
+ int64_t duration_max_read_size = ic->duration_probesize ? ic->duration_probesize >> DURATION_MAX_RETRY_USER : DURATION_MAX_READ_SIZE_DEFAULT;
+ int duration_max_retry = ic->duration_probesize ? DURATION_MAX_RETRY_USER : DURATION_MAX_RETRY_DEFAULT;
int found_duration = 0;
int is_end;
int64_t filesize, offset, duration;
@@ -1861,7 +1864,7 @@ static void estimate_timings_from_pts(AVFormatContext *ic, int64_t old_offset)
filesize = ic->pb ? avio_size(ic->pb) : 0;
do {
is_end = found_duration;
- offset = filesize - (DURATION_MAX_READ_SIZE << retry);
+ offset = filesize - (duration_max_read_size << retry);
if (offset < 0)
offset = 0;
@@ -1870,7 +1873,7 @@ static void estimate_timings_from_pts(AVFormatContext *ic, int64_t old_offset)
for (;;) {
AVStream *st;
FFStream *sti;
- if (read_size >= DURATION_MAX_READ_SIZE << (FFMAX(retry - 1, 0)))
+ if (read_size >= duration_max_read_size << (FFMAX(retry - 1, 0)))
break;
do {
@@ -1924,7 +1927,7 @@ static void estimate_timings_from_pts(AVFormatContext *ic, int64_t old_offset)
}
} while (!is_end &&
offset &&
- ++retry <= DURATION_MAX_RETRY);
+ ++retry <= duration_max_retry);
av_opt_set_int(ic, "skip_changes", 0, AV_OPT_SEARCH_CHILDREN);
diff --git a/libavformat/options_table.h b/libavformat/options_table.h
index b9dca147f9..0cc921a28d 100644
--- a/libavformat/options_table.h
+++ b/libavformat/options_table.h
@@ -108,6 +108,7 @@ static const AVOption avformat_options[] = {
{"max_streams", "maximum number of streams", OFFSET(max_streams), AV_OPT_TYPE_INT, { .i64 = 1000 }, 0, INT_MAX, D },
{"skip_estimate_duration_from_pts", "skip duration calculation in estimate_timings_from_pts", OFFSET(skip_estimate_duration_from_pts), AV_OPT_TYPE_BOOL, {.i64 = 0}, 0, 1, D},
{"max_probe_packets", "Maximum number of packets to probe a codec", OFFSET(max_probe_packets), AV_OPT_TYPE_INT, { .i64 = 2500 }, 0, INT_MAX, D },
+{"durationprobesize", "maximum number of bytes to probe the durations of the streams in estimate_timings_from_pts", OFFSET(duration_probesize), AV_OPT_TYPE_INT64, {.i64 = 0 }, 0, INT64_MAX, D},
{NULL},
};
diff --git a/libavformat/version.h b/libavformat/version.h
index 752aac16f7..a7c80dc564 100644
--- a/libavformat/version.h
+++ b/libavformat/version.h
@@ -31,7 +31,7 @@
#include "version_major.h"
-#define LIBAVFORMAT_VERSION_MINOR 0
+#define LIBAVFORMAT_VERSION_MINOR 1
#define LIBAVFORMAT_VERSION_MICRO 100
#define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
--
2.30.2
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