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@chapter Bitstream Filters

@c man begin BITSTREAM FILTERS

When you configure your FFmpeg build, all the supported bitstream

filters are enabled by default. You can list all available ones using

the configure option @code{--list-bsfs}.

You can disable all the bitstream filters using the configure option

@code{--disable-bsfs}, and selectively enable any bitstream filter using

the option @code{--enable-bsf=BSF}, or you can disable a particular

bitstream filter using the option @code{--disable-bsf=BSF}.

The option @code{-bsfs} of the ff* tools will display the list of

all the supported bitstream filters included in your build.

The ff* tools have a -bsf option applied per stream, taking a

comma-separated list of filters, whose parameters follow the filter

name after a '='.

@example

ffmpeg -i INPUT -c:v copy -bsf:v filter1[=opt1=str1/opt2=str2][,filter2] OUTPUT

@end example

Below is a description of the currently available bitstream filters,

with their parameters, if any.

@section aac_adtstoasc

Convert MPEG-2/4 AAC ADTS to MPEG-4 Audio Specific Configuration

bitstream filter.

This filter creates an MPEG-4 AudioSpecificConfig from an MPEG-2/4

ADTS header and removes the ADTS header.

This is required for example when copying an AAC stream from a raw

ADTS AAC container to a FLV or a MOV/MP4 file.

@section chomp

Remove zero padding at the end of a packet.

@section dump_extra

Add extradata to the beginning of the filtered packets.

The additional argument specifies which packets should be filtered.

It accepts the values:

@table @samp

@item a

add extradata to all key packets, but only if @var{local_header} is

set in the @option{flags2} codec context field

@item k

add extradata to all key packets

@item e

add extradata to all packets

@end table

If not specified it is assumed @samp{k}.

For example the following @command{ffmpeg} command forces a global

header (thus disabling individual packet headers) in the H.264 packets

generated by the @code{libx264} encoder, but corrects them by adding

the header stored in extradata to the key packets:

@example

ffmpeg -i INPUT -map 0 -flags:v +global_header -c:v libx264 -bsf:v dump_extra out.ts

@end example

@section h264_mp4toannexb

Convert an H.264 bitstream from length prefixed mode to start code

prefixed mode (as defined in the Annex B of the ITU-T H.264

specification).

This is required by some streaming formats, typically the MPEG-2

transport stream format ("mpegts").

For example to remux an MP4 file containing an H.264 stream to mpegts

format with @command{ffmpeg}, you can use the command:

@example

ffmpeg -i INPUT.mp4 -codec copy -bsf:v h264_mp4toannexb OUTPUT.ts

@end example

@section imxdump

Modifies the bitstream to fit in MOV and to be usable by the Final Cut

Pro decoder. This filter only applies to the mpeg2video codec, and is

likely not needed for Final Cut Pro 7 and newer with the appropriate

@option{-tag:v}.

For example, to remux 30 MB/sec NTSC IMX to MOV:

@example

ffmpeg -i input.mxf -c copy -bsf:v imxdump -tag:v mx3n output.mov

@end example

@section mjpeg2jpeg

Convert MJPEG/AVI1 packets to full JPEG/JFIF packets.

MJPEG is a video codec wherein each video frame is essentially a

JPEG image. The individual frames can be extracted without loss,

e.g. by

@example

ffmpeg -i ../some_mjpeg.avi -c:v copy frames_%d.jpg

@end example

Unfortunately, these chunks are incomplete JPEG images, because

they lack the DHT segment required for decoding. Quoting from

@url{http://www.digitalpreservation.gov/formats/fdd/fdd000063.shtml}:

Avery Lee, writing in the rec.video.desktop newsgroup in 2001,

commented that "MJPEG, or at least the MJPEG in AVIs having the

MJPG fourcc, is restricted JPEG with a fixed -- and *omitted* --

Huffman table. The JPEG must be YCbCr colorspace, it must be 4:2:2,

and it must use basic Huffman encoding, not arithmetic or

progressive. . . . You can indeed extract the MJPEG frames and

decode them with a regular JPEG decoder, but you have to prepend

the DHT segment to them, or else the decoder won't have any idea

how to decompress the data. The exact table necessary is given in

the OpenDML spec."

This bitstream filter patches the header of frames extracted from an MJPEG

stream (carrying the AVI1 header ID and lacking a DHT segment) to

produce fully qualified JPEG images.

@example

ffmpeg -i mjpeg-movie.avi -c:v copy -bsf:v mjpeg2jpeg frame_%d.jpg

exiftran -i -9 frame*.jpg

ffmpeg -i frame_%d.jpg -c:v copy rotated.avi

@end example

@section mjpega_dump_header

@section movsub

@section mp3_header_decompress

@section mpeg4_unpack_bframes

Unpack DivX-style packed B-frames.

DivX-style packed B-frames are not valid MPEG-4 and were only a

workaround for the broken Video for Windows subsystem.

They use more space, can cause minor AV sync issues, require more

CPU power to decode (unless the player has some decoded picture queue

to compensate the 2,0,2,0 frame per packet style) and cause

trouble if copied into a standard container like mp4 or mpeg-ps/ts,

because MPEG-4 decoders may not be able to decode them, since they are

not valid MPEG-4.

For example to fix an AVI file containing an MPEG-4 stream with

DivX-style packed B-frames using @command{ffmpeg}, you can use the command:

@example

ffmpeg -i INPUT.avi -codec copy -bsf:v mpeg4_unpack_bframes OUTPUT.avi

@end example

@section noise

Damages the contents of packets without damaging the container. Can be

used for fuzzing or testing error resilience/concealment.

Parameters:

A numeral string, whose value is related to how often output bytes will

be modified. Therefore, values below or equal to 0 are forbidden, and

the lower the more frequent bytes will be modified, with 1 meaning

every byte is modified.

@example

ffmpeg -i INPUT -c copy -bsf noise[=1] output.mkv

@end example

applies the modification to every byte.

@section remove_extra

@c man end BITSTREAM FILTERS