Muxers
******

Muxers are configured elements in FFmpeg which allow writing multimedia streams to a particular type of file.

When you configure your FFmpeg 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
===

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 -c:a pcm_u8 -c:v mpeg2video -f crc -

See also the framecrc muxer.

framecrc
========

Per-packet CRC (Cyclic Redundancy Check) testing format.

This muxer computes and prints the Adler-32 CRC for each audio and video packet. 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 packet of the form:

     STREAM_INDEX, PACKET_DTS, PACKET_PTS, PACKET_DURATION, PACKET_SIZE, 0xCRC

CRC is a hexadecimal number 0-padded to 8 digits containing the CRC of the packet.

For example to compute the CRC of the audio and video frames in INPUT, converted to raw audio and video packets, and store it in the file out.crc:

     ffmpeg -i INPUT -f framecrc out.crc

To print the information to stdout, use the command:

     ffmpeg -i INPUT -f framecrc -

With ffmpeg, you can select the output format to which the audio and video frames are encoded before computing the CRC for each packet by specifying the audio and video codec. 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 -c:a pcm_u8 -c:v mpeg2video -f framecrc -

See also the crc muxer.

framemd5
========

Per-packet MD5 testing format.

This muxer computes and prints the MD5 hash for each audio and video packet. By default audio frames are converted to signed 16-bit raw audio and video frames to raw video before computing the hash.

The output of the muxer consists of a line for each audio and video packet of the form:

     STREAM_INDEX, PACKET_DTS, PACKET_PTS, PACKET_DURATION, PACKET_SIZE, MD5

MD5 is a hexadecimal number representing the computed MD5 hash for the packet.

For example to compute the MD5 of the audio and video frames in INPUT, converted to raw audio and video packets, and store it in the file out.md5:

     ffmpeg -i INPUT -f framemd5 out.md5

To print the information to stdout, use the command:

     ffmpeg -i INPUT -f framemd5 -

See also the md5 muxer.

hls
===

Apple HTTP Live Streaming muxer that segments MPEG-TS according to the HTTP Live Streaming specification.

It creates a playlist file and numbered segment files. The output filename specifies the playlist filename; the segment filenames receive the same basename as the playlist, a sequential number and a .ts extension.

     ffmpeg -i in.nut out.m3u8

-hls_time SECONDS
     Set the segment length in seconds.

-hls_list_size SIZE
     Set the maximum number of playlist entries.

-hls_wrap WRAP
     Set the number after which index wraps.

-start_number NUMBER
     Start the sequence from NUMBER.

ico
===

ICO file muxer.

Microsoft's icon file format (ICO) has some strict limitations that should be noted:

  * Size cannot exceed 256 pixels in any dimension

  * Only BMP and PNG images can be stored

  * If a BMP image is used, it must be one of the following pixel formats:

          BMP Bit Depth      FFmpeg Pixel Format
          1bit               pal8
          4bit               pal8
          8bit               pal8
          16bit              rgb555le
          24bit              bgr24
          32bit              bgra

  * If a BMP image is used, it must use the BITMAPINFOHEADER DIB header

  * If a PNG image is used, it must use the rgba pixel format

image2
======

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 -vsync 1 -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 -vsync 1 -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 -frames:v 1 img.jpeg

-start_number NUMBER
     Start the sequence from NUMBER.

The image muxer supports the .Y.U.V image file format. This format is special in that that each image frame consists of three files, for each of the YUV420P components. To read or write this image file format, specify the name of the '.Y' file. The muxer will automatically open the '.U' and '.V' files as required.

md5
===

MD5 testing format.

This muxer computes and prints the MD5 hash 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 hash.

The output of the muxer consists of a single line of the form: MD5=MD5, where MD5 is a hexadecimal number representing the computed MD5 hash.

For example to compute the MD5 hash of the input converted to raw audio and video, and store it in the file out.md5:

     ffmpeg -i INPUT -f md5 out.md5

You can print the MD5 to stdout with the command:

     ffmpeg -i INPUT -f md5 -

See also the framemd5 muxer.

MOV/MP4/ISMV
============

The mov/mp4/ismv muxer supports fragmentation. Normally, a MOV/MP4 file has all the metadata about all packets stored in one location (written at the end of the file, it can be moved to the start for better playback by adding FASTSTART to the MOVFLAGS, or using the qt-faststart tool). A fragmented file consists of a number of fragments, where packets and metadata about these packets are stored together. Writing a fragmented file has the advantage that the file is decodable even if the writing is interrupted (while a normal MOV/MP4 is undecodable if it is not properly finished), and it requires less memory when writing very long files (since writing normal MOV/MP4 files stores info about every single packet in memory until the file is closed). The downside is that it is less compatible with other applications.

Fragmentation is enabled by setting one of the AVOptions that define how to cut the file into fragments:

-moov_size BYTES
     Reserves space for the moov atom at the beginning of the file instead of placing the moov atom at the end. If the space reserved is insufficient, muxing will fail.

-movflags frag_keyframe
     Start a new fragment at each video keyframe.

-frag_duration DURATION
     Create fragments that are DURATION microseconds long.

-frag_size SIZE
     Create fragments that contain up to SIZE bytes of payload data.

-movflags frag_custom
     Allow the caller to manually choose when to cut fragments, by calling av_write_frame(ctx, NULL) to write a fragment with the packets written so far. (This is only useful with other applications integrating libavformat, not from ffmpeg.)

-min_frag_duration DURATION
     Don't create fragments that are shorter than DURATION microseconds long.

If more than one condition is specified, fragments are cut when one of the specified conditions is fulfilled. The exception to this is -min_frag_duration, which has to be fulfilled for any of the other conditions to apply.

Additionally, the way the output file is written can be adjusted through a few other options:

-movflags empty_moov
     Write an initial moov atom directly at the start of the file, without describing any samples in it. Generally, an mdat/moov pair is written at the start of the file, as a normal MOV/MP4 file, containing only a short portion of the file. With this option set, there is no initial mdat atom, and the moov atom only describes the tracks but has a zero duration.

     Files written with this option set do not work in QuickTime. This option is implicitly set when writing ismv (Smooth Streaming) files.

-movflags separate_moof
     Write a separate moof (movie fragment) atom for each track. Normally, packets for all tracks are written in a moof atom (which is slightly more efficient), but with this option set, the muxer writes one moof/mdat pair for each track, making it easier to separate tracks.

     This option is implicitly set when writing ismv (Smooth Streaming) files.

-movflags faststart
     Run a second pass moving the moov atom on top of the file. This operation can take a while, and will not work in various situations such as fragmented output, thus it is not enabled by default.

-movflags rtphint
     Add RTP hinting tracks to the output file.

Smooth Streaming content can be pushed in real time to a publishing point on IIS with this muxer. Example:

     ffmpeg -re <NORMAL INPUT/TRANSCODING OPTIONS> -movflags isml+frag_keyframe -f ismv http://server/publishingpoint.isml/Streams(Encoder1)

mpegts
======

MPEG transport stream muxer.

This muxer implements ISO 13818-1 and part of ETSI EN 300 468.

The muxer options are:

-mpegts_original_network_id NUMBER
     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.

-mpegts_transport_stream_id NUMBER
     Set the transport_stream_id (default 0x0001). This identifies a transponder in DVB.

-mpegts_service_id NUMBER
     Set the service_id (default 0x0001) also known as program in DVB.

-mpegts_pmt_start_pid NUMBER
     Set the first PID for PMT (default 0x1000, max 0x1f00).

-mpegts_start_pid NUMBER
     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 "FFmpeg" and the default for service_name is "Service01".

     ffmpeg -i file.mpg -c 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
====

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
========

Matroska container muxer.

This muxer implements the matroska and webm container specs.

The recognized metadata settings in this muxer are:

title=TITLE NAME
     Name provided to a single track

language=LANGUAGE NAME
     Specifies the language of the track in the Matroska languages form

stereo_mode=MODE
     Stereo 3D video layout of two views in a single video track

     mono
          video is not stereo

     left_right
          Both views are arranged side by side, Left-eye view is on the left

     bottom_top
          Both views are arranged in top-bottom orientation, Left-eye view is at bottom

     top_bottom
          Both views are arranged in top-bottom orientation, Left-eye view is on top

     checkerboard_rl
          Each view is arranged in a checkerboard interleaved pattern, Left-eye view being first

     checkerboard_lr
          Each view is arranged in a checkerboard interleaved pattern, Right-eye view being first

     row_interleaved_rl
          Each view is constituted by a row based interleaving, Right-eye view is first row

     row_interleaved_lr
          Each view is constituted by a row based interleaving, Left-eye view is first row

     col_interleaved_rl
          Both views are arranged in a column based interleaving manner, Right-eye view is first column

     col_interleaved_lr
          Both views are arranged in a column based interleaving manner, Left-eye view is first column

     anaglyph_cyan_red
          All frames are in anaglyph format viewable through red-cyan filters

     right_left
          Both views are arranged side by side, Right-eye view is on the left

     anaglyph_green_magenta
          All frames are in anaglyph format viewable through green-magenta filters

     block_lr
          Both eyes laced in one Block, Left-eye view is first

     block_rl
          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 -c:v libvpx -metadata stereo_mode=left_right -y stereo_clip.webm

segment, stream_segment, ssegment
=================================

Basic stream segmenter.

The segmenter muxer outputs streams to a number of separate files of nearly fixed duration. Output filename pattern can be set in a fashion similar to image2.

stream_segment is a variant of the muxer used to write to streaming output formats, i.e. which do not require global headers, and is recommended for outputting e.g. to MPEG transport stream segments. ssegment is a shorter alias for stream_segment.

Every segment starts with a keyframe of the selected reference stream, which is set through the reference_stream option.

Note that if you want accurate splitting for a video file, you need to make the input key frames correspond to the exact splitting times expected by the segmenter, or the segment muxer will start the new segment with the key frame found next after the specified start time.

The segment muxer works best with a single constant frame rate video.

Optionally it can generate a list of the created segments, by setting the option SEGMENT_LIST. The list type is specified by the SEGMENT_LIST_TYPE option.

The segment muxer supports the following options:

reference_stream SPECIFIER
     Set the reference stream, as specified by the string SPECIFIER. If SPECIFIER is set to auto, the reference is choosen automatically. Otherwise it must be a stream specifier (see the ``Stream specifiers'' chapter in the ffmpeg manual) which specifies the reference stream. The default value is ``auto''.

segment_format FORMAT
     Override the inner container format, by default it is guessed by the filename extension.

segment_list NAME
     Generate also a listfile named NAME. If not specified no listfile is generated.

segment_list_flags FLAGS
     Set flags affecting the segment list generation.

     It currently supports the following flags:

     cache
          Allow caching (only affects M3U8 list files).

     live
          Allow live-friendly file generation.

          This currently only affects M3U8 lists. In particular, write a fake EXT-X-TARGETDURATION duration field at the top of the file, based on the specified SEGMENT_TIME.

     Default value is cache.

segment_list_size SIZE
     Update the list file so that it contains at most the last SIZE segments. If 0 the list file will contain all the segments. Default value is 0.

segment_list type TYPE
     Specify the format for the segment list file.

     The following values are recognized:

     flat
          Generate a flat list for the created segments, one segment per line.

     csv, ext
          Generate a list for the created segments, one segment per line, each line matching the format (comma-separated values):

               SEGMENT_FILENAME,SEGMENT_START_TIME,SEGMENT_END_TIME

          SEGMENT_FILENAME is the name of the output file generated by the muxer according to the provided pattern. CSV escaping (according to RFC4180) is applied if required.

          SEGMENT_START_TIME and SEGMENT_END_TIME specify the segment start and end time expressed in seconds.

          A list file with the suffix ".csv" or ".ext" will auto-select this format.

          ext is deprecated in favor or csv.

     m3u8
          Generate an extended M3U8 file, version 4, compliant with http://tools.ietf.org/id/draft-pantos-http-live-streaming-08.txt.

          A list file with the suffix ".m3u8" will auto-select this format.

     If not specified the type is guessed from the list file name suffix.

segment_time TIME
     Set segment duration to TIME. Default value is "2".

segment_time_delta DELTA
     Specify the accuracy time when selecting the start time for a segment. Default value is "0".

     When delta is specified a key-frame will start a new segment if its PTS satisfies the relation:

          PTS >= start_time - time_delta

     This option is useful when splitting video content, which is always split at GOP boundaries, in case a key frame is found just before the specified split time.

     In particular may be used in combination with the ffmpeg option FORCE_KEY_FRAMES. The key frame times specified by FORCE_KEY_FRAMES may not be set accurately because of rounding issues, with the consequence that a key frame time may result set just before the specified time. For constant frame rate videos a value of 1/2*FRAME_RATE should address the worst case mismatch between the specified time and the time set by FORCE_KEY_FRAMES.

segment_times TIMES
     Specify a list of split points. TIMES contains a list of comma separated duration specifications, in increasing order.

segment_frames FRAMES
     Specify a list of split video frame numbers. FRAMES contains a list of comma separated integer numbers, in increasing order.

     This option specifies to start a new segment whenever a reference stream key frame is found and the sequential number (starting from 0) of the frame is greater or equal to the next value in the list.

segment_wrap LIMIT
     Wrap around segment index once it reaches LIMIT.

segment_start_number NUMBER
     Set the sequence number of the first segment. Defaults to 0.

reset_timestamps 1|0
     Reset timestamps at the begin of each segment, so that each segment will start with near-zero timestamps. It is meant to ease the playback of the generated segments. May not work with some combinations of muxers/codecs. It is set to 0 by default.

Examples
========

  * To remux the content of file in.mkv to a list of segments out-000.nut, out-001.nut, etc., and write the list of generated segments to out.list:

          ffmpeg -i in.mkv -codec copy -map 0 -f segment -segment_list out.list out%03d.nut

  * As the example above, but segment the input file according to the split points specified by the SEGMENT_TIMES option:

          ffmpeg -i in.mkv -codec copy -map 0 -f segment -segment_list out.csv -segment_times 1,2,3,5,8,13,21 out%03d.nut

  * As the example above, but use the ffmpeg FORCE_KEY_FRAMES option to force key frames in the input at the specified location, together with the segment option SEGMENT_TIME_DELTA to account for possible roundings operated when setting key frame times.

          ffmpeg -i in.mkv -force_key_frames 1,2,3,5,8,13,21 -codec:v mpeg4 -codec:a pcm_s16le -map 0 \
          -f segment -segment_list out.csv -segment_times 1,2,3,5,8,13,21 -segment_time_delta 0.05 out%03d.nut

     In order to force key frames on the input file, transcoding is required.

  * Segment the input file by splitting the input file according to the frame numbers sequence specified with the SEGMENT_FRAMES option:

          ffmpeg -i in.mkv -codec copy -map 0 -f segment -segment_list out.csv -segment_frames 100,200,300,500,800 out%03d.nut

  * To convert the in.mkv to TS segments using the libx264 and libfaac encoders:

          ffmpeg -i in.mkv -map 0 -codec:v libx264 -codec:a libfaac -f ssegment -segment_list out.list out%03d.ts

  * Segment the input file, and create an M3U8 live playlist (can be used as live HLS source):

          ffmpeg -re -i in.mkv -codec copy -map 0 -f segment -segment_list playlist.m3u8 \
          -segment_list_flags +live -segment_time 10 out%03d.mkv

mp3
===

The MP3 muxer writes a raw MP3 stream with an ID3v2 header at the beginning and optionally an ID3v1 tag at the end. ID3v2.3 and ID3v2.4 are supported, the id3v2_version option controls which one is used. The legacy ID3v1 tag is not written by default, but may be enabled with the write_id3v1 option.

For seekable output the muxer also writes a Xing frame at the beginning, which contains the number of frames in the file. It is useful for computing duration of VBR files.

The muxer supports writing ID3v2 attached pictures (APIC frames). The pictures are supplied to the muxer in form of a video stream with a single packet. There can be any number of those streams, each will correspond to a single APIC frame. The stream metadata tags TITLE and COMMENT map to APIC DESCRIPTION and PICTURE TYPE respectively. See http://id3.org/id3v2.4.0-frames for allowed picture types.

Note that the APIC frames must be written at the beginning, so the muxer will buffer the audio frames until it gets all the pictures. It is therefore advised to provide the pictures as soon as possible to avoid excessive buffering.

Examples:

Write an mp3 with an ID3v2.3 header and an ID3v1 footer:

     ffmpeg -i INPUT -id3v2_version 3 -write_id3v1 1 out.mp3

Attach a picture to an mp3:

     ffmpeg -i input.mp3 -i cover.png -c copy -metadata:s:v title="Album cover"
     -metadata:s:v comment="Cover (Front)" out.mp3

ogg
===

Ogg container muxer.

-page_duration DURATION
     Preferred page duration, in microseconds. The muxer will attempt to create pages that are approximately DURATION microseconds long. This allows the user to compromise between seek granularity and container overhead. The default is 1 second. A value of 0 will fill all segments, making pages as large as possible. A value of 1 will effectively use 1 packet-per-page in most situations, giving a small seek granularity at the cost of additional container overhead.