ffmpeg-bitstream-filters (1)

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NAME

ffmpeg-bitstream-filters - FFmpeg bitstream filters

DESCRIPTION

This document describes the bitstream filters provided by the libavcodec library.

A bitstream filter operates on the encoded stream data, and performs bitstream level modifications without performing decoding.

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 "--list-bsfs".

You can disable all the bitstream filters using the configure option "--disable-bsfs", and selectively enable any bitstream filter using the option "--enable-bsf=BSF", or you can disable a particular bitstream filter using the option "--disable-bsf=BSF".

The option "-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 '='.

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

Below is a description of the currently available bitstream filters, with their parameters, if any.

aac_adtstoasc

Convert to Audio Specific Configuration bitstream filter.

This filter creates an

AudioSpecificConfig from an header and removes the header.

This is required for example when copying an

stream from a raw container to a or a file.

chomp

Remove zero padding at the end of a packet.

dump_extra

Add extradata to the beginning of the filtered packets.

The additional argument specifies which packets should be filtered. It accepts the values:

a

add extradata to all key packets, but only if local_header is set in the flags2 codec context field

k

add extradata to all key packets

e

add extradata to all packets

If not specified it is assumed k.

For example the following ffmpeg command forces a global header (thus disabling individual packet headers) in the H.264 packets generated by the "libx264" encoder, but corrects them by adding the header stored in extradata to the key packets:

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

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

transport stream format (``mpegts'').

For example to remux an

file containing an H.264 stream to mpegts format with ffmpeg, you can use the command:

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

imxdump

Modifies the bitstream to fit in 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 -tag:v.

For example, to remux 30 MB/sec

to

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

mjpeg2jpeg

Convert packets to full packets.

is a video codec wherein each video frame is essentially a image. The individual frames can be extracted without loss, e.g. by

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

Unfortunately, these chunks are incomplete

images, because they lack the segment required for decoding. Quoting from <www.digitalpreservation.gov/formats/fdd/fdd000063.shtml>:

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

or at least the in AVIs having the fourcc, is restricted with a fixed --- and *omitted* --- Huffman table. The 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 frames and decode them with a regular decoder, but you have to prepend the 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

stream (carrying the header and lacking a segment) to produce fully qualified images.

        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

mjpega_dump_header

movsub

mp3_header_decompress

mpeg4_unpack_bframes

Unpack DivX-style packed B-frames.

DivX-style packed B-frames are not valid

and were only a workaround for the broken Video for Windows subsystem. They use more space, can cause minor sync issues, require more 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 decoders may not be able to decode them, since they are not valid

For example to fix an

file containing an stream with DivX-style packed B-frames using ffmpeg, you can use the command:

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

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.

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

applies the modification to every byte.

remove_extra

SEE ALSO

ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1), libavcodec(3)

AUTHORS

The FFmpeg developers.

For details about the authorship, see the Git history of the project (git://source.ffmpeg.org/ffmpeg e.g. by typing the command git log in the FFmpeg source directory, or browsing the online repository at <source.ffmpeg.org>.

Maintainers for the specific components are listed in the file

in the source code tree.