@c man end DESCRIPTION
+@chapter Detailed description
+@c man begin DETAILED DESCRIPTION
+
+The transcoding process in @command{avconv} for each output can be described by
+the following diagram:
+
+@example
+ _______ ______________ _________ ______________ ________
+| | | | | | | | | |
+| input | demuxer | encoded data | decoder | decoded | encoder | encoded data | muxer | output |
+| file | ---------> | packets | ---------> | frames | ---------> | packets | -------> | file |
+|_______| |______________| |_________| |______________| |________|
+
+@end example
+
+@command{avconv} calls the libavformat library (containing demuxers) to read
+input files and get packets containing encoded data from them. When there are
+multiple input files, @command{avconv} tries to keep them synchronized by
+tracking lowest timestamp on any active input stream.
+
+Encoded packets are then passed to the decoder (unless streamcopy is selected
+for the stream, see further for a description). The decoder produces
+uncompressed frames (raw video/PCM audio/...) which can be processed further by
+filtering (see next section). After filtering the frames are passed to the
+encoder, which encodes them and outputs encoded packets again. Finally those are
+passed to the muxer, which writes the encoded packets to the output file.
+
+@section Filtering
+Before encoding, @command{avconv} can process raw audio and video frames using
+filters from the libavfilter library. Several chained filters form a filter
+graph. @command{avconv} distinguishes between two types of filtergraphs -
+simple and complex.
+
+@subsection Simple filtergraphs
+Simple filtergraphs are those that have exactly one input and output, both of
+the same type. In the above diagram they can be represented by simply inserting
+an additional step between decoding and encoding:
+
+@example
+ _________ __________ ______________
+| | | | | |
+| decoded | simple filtergraph | filtered | encoder | encoded data |
+| frames | -------------------> | frames | ---------> | packets |
+|_________| |__________| |______________|
+
+@end example
+
+Simple filtergraphs are configured with the per-stream @option{-filter} option
+(with @option{-vf} and @option{-af} aliases for video and audio respectively).
+A simple filtergraph for video can look for example like this:
+
+@example
+ _______ _____________ _______ _____ ________
+| | | | | | | | | |
+| input | ---> | deinterlace | ---> | scale | ---> | fps | ---> | output |
+|_______| |_____________| |_______| |_____| |________|
+
+@end example
+
+Note that some filters change frame properties but not frame contents. E.g. the
+@code{fps} filter in the example above changes number of frames, but does not
+touch the frame contents. Another example is the @code{setpts} filter, which
+only sets timestamps and otherwise passes the frames unchanged.
+
+@subsection Complex filtergraphs
+Complex filtergraphs are those which cannot be described as simply a linear
+processing chain applied to one stream. This is the case e.g. when the graph has
+more than one input and/or output, or when output stream type is different from
+input. They can be represented with the following diagram:
+
+@example
+ _________
+| |
+| input 0 |\ __________
+|_________| \ | |
+ \ _________ /| output 0 |
+ \ | | / |__________|
+ _________ \| complex | /
+| | | |/
+| input 1 |---->| filter |\
+|_________| | | \ __________
+ /| graph | \ | |
+ / | | \| output 1 |
+ _________ / |_________| |__________|
+| | /
+| input 2 |/
+|_________|
+
+@end example
+
+Complex filtergraphs are configured with the @option{-filter_complex} option.
+Note that this option is global, since a complex filtergraph by its nature
+cannot be unambiguously associated with a single stream or file.
+
+A trivial example of a complex filtergraph is the @code{overlay} filter, which
+has two video inputs and one video output, containing one video overlaid on top
+of the other. Its audio counterpart is the @code{amix} filter.
+
+@section Stream copy
+Stream copy is a mode selected by supplying the @code{copy} parameter to the
+@option{-codec} option. It makes @command{avconv} omit the decoding and encoding
+step for the specified stream, so it does only demuxing and muxing. It is useful
+for changing the container format or modifying container-level metadata. The
+diagram above will in this case simplify to this:
+
+@example
+ _______ ______________ ________
+| | | | | |
+| input | demuxer | encoded data | muxer | output |
+| file | ---------> | packets | -------> | file |
+|_______| |______________| |________|
+
+@end example
+
+Since there is no decoding or encoding, it is very fast and there is no quality
+loss. However it might not work in some cases because of many factors. Applying
+filters is obviously also impossible, since filters work on uncompressed data.
+
+@c man end DETAILED DESCRIPTION
+
@chapter Stream selection
@c man begin STREAM SELECTION
@item -vframes @var{number} (@emph{output})
Set the number of video frames to record. This is an alias for @code{-frames:v}.
@item -r[:@var{stream_specifier}] @var{fps} (@emph{input/output,per-stream})
-Set frame rate (Hz value, fraction or abbreviation), (default = 25). For output
-streams implies @code{-vsync cfr}.
+Set frame rate (Hz value, fraction or abbreviation).
+
+As an input option, ignore any timestamps stored in the file and instead
+generate timestamps assuming constant frame rate @var{fps}.
+
+As an output option, duplicate or drop input frames to achieve constant output
+frame rate @var{fps} (note that this actually causes the @code{fps} filter to be
+inserted to the end of the corresponding filtergraph).
+
@item -s[:@var{stream_specifier}] @var{size} (@emph{input/output,per-stream})
-Set frame size. The format is @samp{wxh} (default - same as source).
-The following abbreviations are recognized:
+Set frame size.
+
+As an input option, this is a shortcut for the @option{video_size} private
+option, recognized by some demuxers for which the frame size is either not
+stored in the file or is configurable -- e.g. raw video or video grabbers.
+
+As an output option, this inserts the @code{scale} video filter to the
+@emph{end} of the corresponding filtergraph. Please use the @code{scale} filter
+directly to insert it at the beginning or some other place.
+
+The format is @samp{wxh} (default - same as source). The following
+abbreviations are recognized:
@table @samp
@item sqcif
128x96
@item -vcodec @var{codec} (@emph{output})
Set the video codec. This is an alias for @code{-codec:v}.
-@item -same_quant
-Use same quantizer as source (implies VBR).
-
-Note that this is NOT SAME QUALITY. Do not use this option unless you know you
-need it.
-@item -pass @var{n}
+@item -pass[:@var{stream_specifier}] @var{n} (@emph{output,per-stream})
Select the pass number (1 or 2). It is used to do two-pass
video encoding. The statistics of the video are recorded in the first
pass into a log file (see also the option -passlogfile),
avconv -i foo.mov -c:v libxvid -pass 1 -an -f rawvideo -y /dev/null
@end example
-@item -passlogfile @var{prefix} (@emph{global})
+@item -passlogfile[:@var{stream_specifier}] @var{prefix} (@emph{output,per-stream})
Set two-pass log file name prefix to @var{prefix}, the default file name
prefix is ``av2pass''. The complete file name will be
@file{PREFIX-N.log}, where N is a number specific to the output
@item -sample_fmt[:@var{stream_specifier}] @var{sample_fmt} (@emph{output,per-stream})
Set the audio sample format. Use @code{-sample_fmts} to get a list
of supported sample formats.
+@item -af @var{filter_graph} (@emph{output})
+@var{filter_graph} is a description of the filter graph to apply to
+the input audio.
+Use the option "-filters" to show all the available filters (including
+also sources and sinks). This is an alias for @code{-filter:a}.
@end table
@section Advanced Audio options:
Disable subtitle recording.
@end table
-@section Audio/Video grab options
-
-@table @option
-@item -isync (@emph{global})
-Synchronize read on input.
-@end table
-
@section Advanced options
@table @option
the parameter is the maximum samples per second by which the audio is changed.
-async 1 is a special case where only the start of the audio stream is corrected
without any later correction.
+This option has been deprecated. Use the @code{asyncts} audio filter instead.
@item -copyts
Copy timestamps from input to output.
@item -copytb
Copy input stream time base from input to output when stream copying.
-@item -shortest
+@item -shortest (@emph{output})
Finish encoding when the shortest input stream ends.
@item -dts_delta_threshold
Timestamp discontinuity delta threshold.
Output link labels are referred to with @option{-map}. Unlabeled outputs are
added to the first output file.
+Note that with this option it is possible to use only lavfi sources without
+normal input files.
+
For example, to overlay an image over video
@example
avconv -i video.mkv -i image.png -filter_complex '[0:v][1:v]overlay[out]' -map
@example
avconv -i video.mkv -i image.png -filter_complex 'overlay' out.mkv
@end example
+
+To generate 5 seconds of pure red video using lavfi @code{color} source:
+@example
+avconv -filter_complex 'color=red' -t 5 out.mkv
+@end example
@end table
@c man end OPTIONS
projects / ffmpeg / blobdiff