ffmpeg-bitstream-filters - Online in the Cloud

PROGRAM:

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 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.

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 MPEG-2 transport stream format
("mpegts").

For example to remux an MP4 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 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 -tag:v.

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

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

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

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

Unfortunately, these chunks are incomplete JPEG images, because they lack the DHT segment
required for decoding. Quoting from
<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.

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 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 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

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