Muxers are configured elements in Libav which allow writing multimedia streams to a particular type of file.
When you configure your Libav build, all the supported muxers
are enabled by default. You can list all available muxers using the
configure option --list-muxers
.
You can disable all the muxers with the configure option
--disable-muxers
and selectively enable / disable single muxers
with the options --enable-muxer=MUXER
/
--disable-muxer=MUXER
.
The option -formats
of the ff* tools will display the list of
enabled muxers.
A description of some of the currently available muxers follows.
CRC (Cyclic Redundancy Check) testing format.
This muxer computes and prints the Adler-32 CRC of all the input audio and video frames. By default audio frames are converted to signed 16-bit raw audio and video frames to raw video before computing the CRC.
The output of the muxer consists of a single line of the form: CRC=0xCRC, where CRC is a hexadecimal number 0-padded to 8 digits containing the CRC for all the decoded input frames.
For example to compute the CRC of the input, and store it in the file ‘out.crc’:
ffmpeg -i INPUT -f crc out.crc |
You can print the CRC to stdout with the command:
ffmpeg -i INPUT -f crc - |
You can select the output format of each frame with ‘ffmpeg’ by specifying the audio and video codec and format. For example to compute the CRC of the input audio converted to PCM unsigned 8-bit and the input video converted to MPEG-2 video, use the command:
ffmpeg -i INPUT -acodec pcm_u8 -vcodec mpeg2video -f crc - |
See also the framecrc
muxer (see framecrc).
Per-frame CRC (Cyclic Redundancy Check) testing format.
This muxer computes and prints the Adler-32 CRC for each decoded audio and video frame. By default audio frames are converted to signed 16-bit raw audio and video frames to raw video before computing the CRC.
The output of the muxer consists of a line for each audio and video frame of the form: stream_index, frame_dts, frame_size, 0xCRC, where CRC is a hexadecimal number 0-padded to 8 digits containing the CRC of the decoded frame.
For example to compute the CRC of each decoded frame in the input, and store it in the file ‘out.crc’:
ffmpeg -i INPUT -f framecrc out.crc |
You can print the CRC of each decoded frame to stdout with the command:
ffmpeg -i INPUT -f framecrc - |
You can select the output format of each frame with ‘ffmpeg’ by specifying the audio and video codec and format. For example, to compute the CRC of each decoded input audio frame converted to PCM unsigned 8-bit and of each decoded input video frame converted to MPEG-2 video, use the command:
ffmpeg -i INPUT -acodec pcm_u8 -vcodec mpeg2video -f framecrc - |
See also the crc
muxer (see crc).
Image file muxer.
The image file muxer writes video frames to image files.
The output filenames are specified by a pattern, which can be used to produce sequentially numbered series of files. The pattern may contain the string "%d" or "%0Nd", this string specifies the position of the characters representing a numbering in the filenames. If the form "%0Nd" is used, the string representing the number in each filename is 0-padded to N digits. The literal character ’%’ can be specified in the pattern with the string "%%".
If the pattern contains "%d" or "%0Nd", the first filename of the file list specified will contain the number 1, all the following numbers will be sequential.
The pattern may contain a suffix which is used to automatically determine the format of the image files to write.
For example the pattern "img-%03d.bmp" will specify a sequence of filenames of the form ‘img-001.bmp’, ‘img-002.bmp’, ..., ‘img-010.bmp’, etc. The pattern "img%%-%d.jpg" will specify a sequence of filenames of the form ‘img%-1.jpg’, ‘img%-2.jpg’, ..., ‘img%-10.jpg’, etc.
The following example shows how to use ‘ffmpeg’ for creating a sequence of files ‘img-001.jpeg’, ‘img-002.jpeg’, ..., taking one image every second from the input video:
ffmpeg -i in.avi -r 1 -f image2 'img-%03d.jpeg' |
Note that with ‘ffmpeg’, if the format is not specified with the
-f
option and the output filename specifies an image file
format, the image2 muxer is automatically selected, so the previous
command can be written as:
ffmpeg -i in.avi -r 1 'img-%03d.jpeg' |
Note also that the pattern must not necessarily contain "%d" or "%0Nd", for example to create a single image file ‘img.jpeg’ from the input video you can employ the command:
ffmpeg -i in.avi -f image2 -vframes 1 img.jpeg |
MPEG transport stream muxer.
This muxer implements ISO 13818-1 and part of ETSI EN 300 468.
The muxer options are:
Set the original_network_id (default 0x0001). This is unique identifier of a network in DVB. Its main use is in the unique identification of a service through the path Original_Network_ID, Transport_Stream_ID.
Set the transport_stream_id (default 0x0001). This identifies a transponder in DVB.
Set the service_id (default 0x0001) also known as program in DVB.
Set the first PID for PMT (default 0x1000, max 0x1f00).
Set the first PID for data packets (default 0x0100, max 0x0f00).
The recognized metadata settings in mpegts muxer are service_provider
and service_name
. If they are not set the default for
service_provider
is "Libav" and the default for
service_name
is "Service01".
ffmpeg -i file.mpg -acodec copy -vcodec copy \ -mpegts_original_network_id 0x1122 \ -mpegts_transport_stream_id 0x3344 \ -mpegts_service_id 0x5566 \ -mpegts_pmt_start_pid 0x1500 \ -mpegts_start_pid 0x150 \ -metadata service_provider="Some provider" \ -metadata service_name="Some Channel" \ -y out.ts |
Null muxer.
This muxer does not generate any output file, it is mainly useful for testing or benchmarking purposes.
For example to benchmark decoding with ‘ffmpeg’ you can use the command:
ffmpeg -benchmark -i INPUT -f null out.null |
Note that the above command does not read or write the ‘out.null’ file, but specifying the output file is required by the ‘ffmpeg’ syntax.
Alternatively you can write the command as:
ffmpeg -benchmark -i INPUT -f null - |
Matroska container muxer.
This muxer implements the matroska and webm container specs.
The recognized metadata settings in this muxer are:
Name provided to a single track
Specifies the language of the track in the Matroska languages form
Stereo 3D video layout of two views in a single video track
video is not stereo
Both views are arranged side by side, Left-eye view is on the left
Both views are arranged in top-bottom orientation, Left-eye view is at bottom
Both views are arranged in top-bottom orientation, Left-eye view is on top
Each view is arranged in a checkerboard interleaved pattern, Left-eye view being first
Each view is arranged in a checkerboard interleaved pattern, Right-eye view being first
Each view is constituted by a row based interleaving, Right-eye view is first row
Each view is constituted by a row based interleaving, Left-eye view is first row
Both views are arranged in a column based interleaving manner, Right-eye view is first column
Both views are arranged in a column based interleaving manner, Left-eye view is first column
All frames are in anaglyph format viewable through red-cyan filters
Both views are arranged side by side, Right-eye view is on the left
All frames are in anaglyph format viewable through green-magenta filters
Both eyes laced in one Block, Left-eye view is first
Both eyes laced in one Block, Right-eye view is first
For example a 3D WebM clip can be created using the following command line:
ffmpeg -i sample_left_right_clip.mpg -an -vcodec libvpx -metadata STEREO_MODE=left_right -y stereo_clip.webm |
This document was generated by mdx on February 3, 2021 using texi2html 1.82.