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.\" ========================================================================
.\"
.IX Title "FFMPEG-BITSTREAM-FILTERS 1"
.TH FFMPEG-BITSTREAM-FILTERS 1 "2013-04-21" " " " "
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
ffmpeg\-bitstream\-filters \- FFmpeg bitstream filters
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This document describes the bitstream filters provided by the
libavcodec library.
.PP
A bitstream filter operates on the encoded stream data, and performs
bitstream level modifications without performing decoding.
.SH "BITSTREAM FILTERS"
.IX Header "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 \f(CW\*(C`\-\-list\-bsfs\*(C'\fR.
.PP
You can disable all the bitstream filters using the configure option
\&\f(CW\*(C`\-\-disable\-bsfs\*(C'\fR, and selectively enable any bitstream filter using
the option \f(CW\*(C`\-\-enable\-bsf=BSF\*(C'\fR, or you can disable a particular
bitstream filter using the option \f(CW\*(C`\-\-disable\-bsf=BSF\*(C'\fR.
.PP
The option \f(CW\*(C`\-bsfs\*(C'\fR of the ff* tools will display the list of
all the supported bitstream filters included in your build.
.PP
Below is a description of the currently available bitstream filters.
.SS "aac_adtstoasc"
.IX Subsection "aac_adtstoasc"
.SS "chomp"
.IX Subsection "chomp"
.SS "dump_extradata"
.IX Subsection "dump_extradata"
.SS "h264_mp4toannexb"
.IX Subsection "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).
.PP
This is required by some streaming formats, typically the \s-1MPEG\-2\s0
transport stream format (\*(L"mpegts\*(R").
.PP
For example to remux an \s-1MP4\s0 file containing an H.264 stream to mpegts
format with \fBffmpeg\fR, you can use the command:
.PP
.Vb 1
\&        ffmpeg \-i INPUT.mp4 \-codec copy \-bsf:v h264_mp4toannexb OUTPUT.ts
.Ve
.SS "imx_dump_header"
.IX Subsection "imx_dump_header"
.SS "mjpeg2jpeg"
.IX Subsection "mjpeg2jpeg"
Convert \s-1MJPEG/AVI1\s0 packets to full \s-1JPEG/JFIF\s0 packets.
.PP
\&\s-1MJPEG\s0 is a video codec wherein each video frame is essentially a
\&\s-1JPEG\s0 image. The individual frames can be extracted without loss,
e.g. by
.PP
.Vb 1
\&        ffmpeg \-i ../some_mjpeg.avi \-c:v copy frames_%d.jpg
.Ve
.PP
Unfortunately, these chunks are incomplete \s-1JPEG\s0 images, because
they lack the \s-1DHT\s0 segment required for decoding. Quoting from
<\fBhttp://www.digitalpreservation.gov/formats/fdd/fdd000063.shtml\fR>:
.PP
Avery Lee, writing in the rec.video.desktop newsgroup in 2001,
commented that \*(L"\s-1MJPEG\s0, or at least the \s-1MJPEG\s0 in AVIs having the
\&\s-1MJPG\s0 fourcc, is restricted \s-1JPEG\s0 with a fixed \*(-- and *omitted* \*(--
Huffman table. The \s-1JPEG\s0 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 \s-1MJPEG\s0 frames and
decode them with a regular \s-1JPEG\s0 decoder, but you have to prepend
the \s-1DHT\s0 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.\*(R"
.PP
This bitstream filter patches the header of frames extracted from an \s-1MJPEG\s0
stream (carrying the \s-1AVI1\s0 header \s-1ID\s0 and lacking a \s-1DHT\s0 segment) to
produce fully qualified \s-1JPEG\s0 images.
.PP
.Vb 3
\&        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
.Ve
.SS "mjpega_dump_header"
.IX Subsection "mjpega_dump_header"
.SS "movsub"
.IX Subsection "movsub"
.SS "mp3_header_compress"
.IX Subsection "mp3_header_compress"
.SS "mp3_header_decompress"
.IX Subsection "mp3_header_decompress"
.SS "noise"
.IX Subsection "noise"
.SS "remove_extradata"
.IX Subsection "remove_extradata"
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fIffmpeg\fR\|(1), \fIffplay\fR\|(1), \fIffprobe\fR\|(1), \fIffserver\fR\|(1), \fIlibavcodec\fR\|(3)
.SH "AUTHORS"
.IX Header "AUTHORS"
The FFmpeg developers.
.PP
For details about the authorship, see the Git history of the project
(git://source.ffmpeg.org/ffmpeg), e.g. by typing the command
\&\fBgit log\fR in the FFmpeg source directory, or browsing the
online repository at <\fBhttp://source.ffmpeg.org\fR>.
.PP
Maintainers for the specific components are listed in the file
\&\fI\s-1MAINTAINERS\s0\fR in the source code tree.