githubmirror/FFmpeg

doc/formats.texi
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Nicolas Gaullier
avformat/demux: add duration_probesize AVOption
02 апр 2024, 20:53
02 апр 2024, 20:53ed93630
@chapter Format Options
@c man begin FORMAT OPTIONS

The libavformat library provides some generic global options, which
can be set on all the muxers and demuxers. In addition each muxer or
demuxer may support so-called private options, which are specific for
that component.

Options may be set by specifying -@var{option} @var{value} in the
FFmpeg tools, or by setting the value explicitly in the
@code{AVFormatContext} options or using the @file{libavutil/opt.h} API
for programmatic use.

The list of supported options follows:

@table @option
@item avioflags @var{flags} (@emph{input/output})
Possible values:
@table @samp
@item direct
Reduce buffering.
@end table

@item probesize @var{integer} (@emph{input})
Set probing size in bytes, i.e. the size of the data to analyze to get
stream information. A higher value will enable detecting more
information in case it is dispersed into the stream, but will increase
latency. Must be an integer not lesser than 32. It is 5000000 by default.

@item max_probe_packets @var{integer} (@emph{input})
Set the maximum number of buffered packets when probing a codec.
Default is 2500 packets.

@item packetsize @var{integer} (@emph{output})
Set packet size.

@item fflags @var{flags}
Set format flags. Some are implemented for a limited number of formats.

Possible values for input files:
@table @samp
@item discardcorrupt
Discard corrupted packets.
@item fastseek
Enable fast, but inaccurate seeks for some formats.
@item genpts
Generate missing PTS if DTS is present.
@item igndts
Ignore DTS if PTS is also set. In case the PTS is set, the DTS value
is set to NOPTS. This is ignored when the @code{nofillin} flag is set.
@item ignidx
Ignore index.
@item nobuffer
Reduce the latency introduced by buffering during initial input streams analysis.
@item nofillin
Do not fill in missing values in packet fields that can be exactly calculated.
@item noparse
Disable AVParsers, this needs @code{+nofillin} too.
@item sortdts
Try to interleave output packets by DTS. At present, available only for AVIs with an index.
@end table

Possible values for output files:
@table @samp
@item autobsf
Automatically apply bitstream filters as required by the output format. Enabled by default.
@item bitexact
Only write platform-, build- and time-independent data.
This ensures that file and data checksums are reproducible and match between
platforms. Its primary use is for regression testing.
@item flush_packets
Write out packets immediately.
@item shortest
Stop muxing at the end of the shortest stream.
It may be needed to increase max_interleave_delta to avoid flushing the longer
streams before EOF.
@end table

@item seek2any @var{integer} (@emph{input})
Allow seeking to non-keyframes on demuxer level when supported if set to 1.
Default is 0.

@item analyzeduration @var{integer} (@emph{input})
Specify how many microseconds are analyzed to probe the input. A
higher value will enable detecting more accurate information, but will
increase latency. It defaults to 5,000,000 microseconds = 5 seconds.

@item cryptokey @var{hexadecimal string} (@emph{input})
Set decryption key.

@item indexmem @var{integer} (@emph{input})
Set max memory used for timestamp index (per stream).

@item rtbufsize @var{integer} (@emph{input})
Set max memory used for buffering real-time frames.

@item fdebug @var{flags} (@emph{input/output})
Print specific debug info.

Possible values:
@table @samp
@item ts
@end table

@item max_delay @var{integer} (@emph{input/output})
Set maximum muxing or demuxing delay in microseconds.

@item fpsprobesize @var{integer} (@emph{input})
Set number of frames used to probe fps.

@item audio_preload @var{integer} (@emph{output})
Set microseconds by which audio packets should be interleaved earlier.

@item chunk_duration @var{integer} (@emph{output})
Set microseconds for each chunk.

@item chunk_size @var{integer} (@emph{output})
Set size in bytes for each chunk.

@item err_detect, f_err_detect @var{flags} (@emph{input})
Set error detection flags. @code{f_err_detect} is deprecated and
should be used only via the @command{ffmpeg} tool.

Possible values:
@table @samp
@item crccheck
Verify embedded CRCs.
@item bitstream
Detect bitstream specification deviations.
@item buffer
Detect improper bitstream length.
@item explode
Abort decoding on minor error detection.
@item careful
Consider things that violate the spec and have not been seen in the
wild as errors.
@item compliant
Consider all spec non compliancies as errors.
@item aggressive
Consider things that a sane encoder should not do as an error.
@end table

@item max_interleave_delta @var{integer} (@emph{output})
Set maximum buffering duration for interleaving. The duration is
expressed in microseconds, and defaults to 10000000 (10 seconds).

To ensure all the streams are interleaved correctly, libavformat will
wait until it has at least one packet for each stream before actually
writing any packets to the output file. When some streams are
"sparse" (i.e. there are large gaps between successive packets), this
can result in excessive buffering.

This field specifies the maximum difference between the timestamps of the
first and the last packet in the muxing queue, above which libavformat
will output a packet regardless of whether it has queued a packet for all
the streams.

If set to 0, libavformat will continue buffering packets until it has
a packet for each stream, regardless of the maximum timestamp
difference between the buffered packets.

@item use_wallclock_as_timestamps @var{integer} (@emph{input})
Use wallclock as timestamps if set to 1. Default is 0.

@item avoid_negative_ts @var{integer} (@emph{output})

Possible values:
@table @samp
@item make_non_negative
Shift timestamps to make them non-negative.
Also note that this affects only leading negative timestamps, and not
non-monotonic negative timestamps.
@item make_zero
Shift timestamps so that the first timestamp is 0.
@item auto (default)
Enables shifting when required by the target format.
@item disabled
Disables shifting of timestamp.
@end table

When shifting is enabled, all output timestamps are shifted by the
same amount. Audio, video, and subtitles desynching and relative
timestamp differences are preserved compared to how they would have
been without shifting.

@item skip_initial_bytes @var{integer} (@emph{input})
Set number of bytes to skip before reading header and frames if set to 1.
Default is 0.

@item correct_ts_overflow @var{integer} (@emph{input})
Correct single timestamp overflows if set to 1. Default is 1.

@item flush_packets @var{integer} (@emph{output})
Flush the underlying I/O stream after each packet. Default is -1 (auto), which
means that the underlying protocol will decide, 1 enables it, and has the
effect of reducing the latency, 0 disables it and may increase IO throughput in
some cases.

@item output_ts_offset @var{offset} (@emph{output})
Set the output time offset.

@var{offset} must be a time duration specification,
see @ref{time duration syntax,,the Time duration section in the ffmpeg-utils(1) manual,ffmpeg-utils}.

The offset is added by the muxer to the output timestamps.

Specifying a positive offset means that the corresponding streams are
delayed bt the time duration specified in @var{offset}. Default value
is @code{0} (meaning that no offset is applied).

@item format_whitelist @var{list} (@emph{input})
"," separated list of allowed demuxers. By default all are allowed.

@item dump_separator @var{string} (@emph{input})
Separator used to separate the fields printed on the command line about the
Stream parameters.
For example, to separate the fields with newlines and indentation:
@example
ffprobe -dump_separator "
                          "  -i ~/videos/matrixbench_mpeg2.mpg
@end example

@item max_streams @var{integer} (@emph{input})
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 if it requires an additional probing for PTS at end of file.
At present, applicable for MPEG-PS and MPEG-TS.

@item duration_probesize @var{integer} (@emph{input})
Set probing size, in bytes, for input duration estimation when it actually requires
an additional probing for PTS at end of file (at present: MPEG-PS and MPEG-TS).
It is aimed at users interested in better durations probing for itself, or indirectly
because using the concat demuxer, for example.
The typical use case is an MPEG-TS CBR with a high bitrate, high video buffering and
ending cleaning with similar PTS for video and audio: in such a scenario, the large
physical gap between the last video packet and the last audio packet makes it necessary
to read many bytes in order to get the video stream duration.
Another use case is where the default probing behaviour only reaches a single video frame which is
not the last one of the stream due to frame reordering, so the duration is not accurate.
Setting this option has a performance impact even for small files because the probing
size is fixed.
Default behaviour is a general purpose trade-off, largely adaptive, but the probing size
will not be 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.

Possible values:
@table @samp
@item very
strictly conform to an older more strict version of the spec or reference software
@item strict
strictly conform to all the things in the spec no matter what consequences
@item normal

@item unofficial
allow unofficial extensions
@item experimental
allow non standardized experimental things, experimental
(unfinished/work in progress/not well tested) decoders and encoders.
Note: experimental decoders can pose a security risk, do not use this for
decoding untrusted input.
@end table

@end table

@c man end FORMAT OPTIONS

@anchor{Format stream specifiers}
@section Format stream specifiers

Format stream specifiers allow selection of one or more streams that
match specific properties.

The exact semantics of stream specifiers is defined by the
@code{avformat_match_stream_specifier()} function declared in the
@file{libavformat/avformat.h} header and documented in the
@ref{Stream specifiers,,Stream specifiers section in the ffmpeg(1) manual,ffmpeg}.

@ifclear config-writeonly
@include demuxers.texi
@end ifclear
@ifclear config-readonly
@include muxers.texi
@end ifclear
@include metadata.texi