[FFmpeg-devel] [PATCH v3 1/1] avformat/demux: Add durationprobesize AVOption
Stefano Sabatini
stefasab at gmail.com
Tue Mar 19 13:06:01 EET 2024
Sorry for the slow replay.
On date Monday 2024-03-11 16:57:19 +0100, Nicolas Gaullier wrote:
> 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
nit++: missing dot at end of sentence
> +
> 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.
consistency: PTS
> At present, applicable for MPEG-PS and MPEG-TS.
>
> + at item durationprobesize @var{integer} (@emph{input})
I'd go with duration_probesize, as it looks more readable (although we
also have fpsprobesize), but most option names are splitting the name
and this looks way more readable.
> +Set probing size for input duration estimation when it actually requires an additional probing
> +for pts at end of file.
consistency: PTS
also specify the measure unit of the value
> +At present, applicable for MPEG-PS and MPEG-TS.
I'm still confused why this should not be applicated to other formats
as well.
> +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.
If this is bytes, then it might be confusing using K and M, maybe
I'd use Ki and Mi to prevent the possible confusion.
> +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
nit: let's favor long forms to help readability (seealso or equivalent)
> */
> 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
ditto
> + */
> + 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
nit:
DURATION_DEFAULT_MAX_READ_SIZE
DURATION_DEFAULT_MAX_RETRY_DEFAULT
DURATION_MAX_RETRY 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;
nit: I find the right shift followed by the leftshift a bit confusing,
but probably there is no simple way to prevent it
> + 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},
duration_probesize ?
[...]
Thanks
More information about the ffmpeg-devel
mailing list