Codecs¶

What the engine can decode (as inputs) and encode (as outputs[].video_codec / audio_codec), by profile. Every codec here is in-tree libavcodec, with no external library, LGPL-clean (the GPL variant additionally links libx264 for H.264 encode).

Lean (all builds)¶

Intermediate (+ over lean)¶

The native codec batch (spec 0016) all in-tree and LGPL-clean:

External encoders (spec 0018)¶

The LGPL/BSD encoder libraries cross-compiled into the build (build/deps.sh) and linked by libav: external code, but all LGPL-compatible, so both licence variants get them. Encode uses the lib* name (e.g. audio_codec: "libopus"); the produced stream probes back to the plain codec name (opus).

All are software, single-threaded, and VP9 encode in particular is slow without threads, so pick VP8 unless VP9 is required. libvpx's encoder uses setjmp/longjmp, lowered to wasm exception-handling; the afmpeg runtime enables that feature to load the module.

Subtitles (spec 0019)¶

The intermediate profile also enables the subtitle codec batch, which rides the dedicated subtitle transcode lane (decode → re-encode), not the filter graph. Drive it with subtitle_codec on a subtitle output stream; see the job spec, for burning subtitles into video use the subtitles/ass/drawtext filters instead.

(movtext is the configure-time name; the encoder is mov_text at runtime; the MP4/MOV timed-text codec.)

Notes¶

• DTS is decode-only (dca): the encoder is experimental in FFmpeg and left out (D-0016-B). TrueHD/AMR are not in this batch.
• eq is not a codec; see filters.
• HEVC/AV1 encode live in the full profile below (native only). AV1 decode is via libdav1d (spec 0023 D-0023-C), in the intermediate profile (and full), both variants, both runtimes. FFmpeg's in-tree av1 decoder is hwaccel-only, so software AV1 decode needs the lib. dav1d ships a threaded-wasm build by default; ours is built single-threaded for WASM (it runs on wazero, which has no threads, so decode is correct but slower than the threaded native driver). So intermediate decodes AV1 identically on the .wasm module and the native driver.
• Patent posture: AC-3, DTS, MPEG-2/4, VC-1 carry codec patents, the same class as the H.264/HEVC the engine already decodes; see the licensing explanation.
• The decode-only codecs (prores, dnxhd, mpeg2video, vc1, …) are enabled in the build but need a licence-clean media corpus to exercise end-to-end (spec 0016 §8): the codecs with an encoder are verified by an encode→decode round-trip.

Full (native only, + over intermediate)¶

The heavy next-generation encoders (spec 0023). They are thread- and SIMD-hungry and impractical in WASM, so they ship only in the native driver's full profile (ffmpeg-wasi-driver-linux-amd64-full-<variant>, spec 0028), never in any .wasm.

HEVC decode needs no full profile: the native hevc decoder is in every build (lean and up). HW-accel encoders (NVENC/VAAPI/…) are the remaining full members, deferred until a GPU is available.