Containers, bitstream filters & protocols¶

What the engine can read (demuxers), write (muxers), and rewrite in passing (bitstream filters), by profile. This is the container half of the picture; codecs is the codec half and filters the filtergraph half.

The build starts from --disable-everything and enables an explicit allowlist, so a format not listed here is not present — the muxer cannot be resolved and the job fails with process: cannot resolve output format.

How a container is chosen¶

• Reading. libavformat probes the input. Set inputs[].format to force a demuxer by name instead — required for headerless input such as rawvideo or raw PCM, where there is nothing to probe. See the job spec.
• Writing. The muxer is guessed from the output path's extension. Set outputs[].format to force one by name — required wherever the extension does not imply it (hls, dash, segment) or where you want a different muxer than the extension suggests.
• Muxer options go in outputs[].format_options, never in outputs[].options (which reaches the encoder). Segment timing and naming, fragmentation flags and playlist settings are all muxer options.

Lean (all builds)¶

The asymmetry is deliberate: lean reads Ogg, AAC-in-ADTS, FLAC and raw streams but writes only the seven muxers above. Writing an .ogg, .aac or .flac file needs the intermediate profile.

concat is the demuxer behind inputs[].concat — a stream-copy join of like-codec files. It is present in every profile.

Intermediate (+ over lean)¶

The native container batch, all in-tree and LGPL-clean, no external library:

Fragmented MP4 / CMAF is not a separate muxer — it is the mp4 muxer driven with format_options: {"movflags": "+frag_keyframe+empty_moov"}, available in every profile.

Segmenting outputs write a set of files¶

hls, dash, segment and stream_segment write a playlist or manifest plus the segment files beside it on the mounted filesystem. The output's path is the playlist; the segments follow whatever naming pattern you set in format_options. Such an output reports "segmented": true in its result entry rather than listing a single file.

{"op":"process","version":5,"inputs":[{"path":"in.mp4"}],"filter":"[0:v]null[v]",
 "outputs":[{"path":"stream.m3u8","map":["[v]"],"format":"hls","video_codec":"libopenh264",
   "format_options":{"hls_time":"4","hls_segment_filename":"seg_%03d.ts","hls_list_size":"0"}}]}

Nothing is uploaded. HLS and DASH here mean writing the files; serving them is the host's job — the engine has no network (why).

Full (native)¶

The full profile adds no containers. Its additions are the heavy HEVC and AV1 encoders; the format set is identical to intermediate.

Bitstream filters¶

The same four in every profile — a stream copy sometimes needs a container-specific rewrite of the bitstream even though nothing is decoded:

You rarely need to name one. The muxer auto-inserts whichever the container requires, so an MP4 → MPEG-TS remux picks up h264_mp4toannexb on its own. Use outputs[].bitstream_filters to force a specific chain, or the value "none" to suppress the automatic one:

{"outputs":[{"path":"out.ts","map":["0:v","0:a"],
  "video_codec":"copy","audio_codec":"copy",
  "bitstream_filters":{"0:v":"h264_mp4toannexb"}}]}

Naming a BSF this build does not carry fails with process: bad bitstream filter.

Protocols¶

Two, in every profile:

libav* is built --disable-network, so no network protocol exists — no http, https, rtmp, srt, rtsp or tcp. A URL is not an openable path; see limits.

Related¶

• Codecs — what can be decoded and encoded inside these containers.
• The job-spec vocabulary — inputs[].format, outputs[].format, format_options and bitstream_filters.
• Build options — where the allowlist above is defined.