=head1 NAME
ffmpeg-bitstream-filters - FFmpeg bitstream filters
=head1 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.
=head1 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 C<--list-bsfs>.
You can disable all the bitstream filters using the configure option
C<--disable-bsfs>, and selectively enable any bitstream filter using
the option C<--enable-bsf=BSF>, or you can disable a particular
bitstream filter using the option C<--disable-bsf=BSF>.
The option C<-bsfs> of the ff* tools will display the list of
all the supported bitstream filters included in your build.
Below is a description of the currently available bitstream filters.
=head2 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.
=head2 chomp
Remove zero padding at the end of a packet.
=head2 dump_extra
Add extradata to the beginning of the filtered packets.
The additional argument specifies which packets should be filtered.
It accepts the values:
=over 4
=item B<a>
add extradata to all key packets, but only if I<local_header> is
set in the B<flags2> codec context field
=item B<k>
add extradata to all key packets
=item B<e>
add extradata to all packets
=back
If not specified it is assumed B<k>.
For example the following B<ffmpeg> command forces a global
header (thus disabling individual packet headers) in the H.264 packets
generated by the C<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
=head2 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 B<ffmpeg>, you can use the command:
ffmpeg -i INPUT.mp4 -codec copy -bsf:v h264_mp4toannexb OUTPUT.ts
=head2 imx_dump_header
=head2 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
E<lt>B<http://www.digitalpreservation.gov/formats/fdd/fdd000063.shtml>E<gt>:
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
=head2 mjpega_dump_header
=head2 movsub
=head2 mp3_header_compress
=head2 mp3_header_decompress
=head2 noise
=head2 remove_extra
=head1 SEE ALSO
ffmpeg(1), ffplay(1), ffprobe(1), ffserver(1), libavcodec(3)
=head1 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
B<git log> in the FFmpeg source directory, or browsing the
online repository at E<lt>B<http://source.ffmpeg.org>E<gt>.
Maintainers for the specific components are listed in the file
F<MAINTAINERS> in the source code tree.