ffmpeg-build

Reproducible builds of a minimal static ffmpeg for Tango.

Tango doesn't link libav* — it ships a standalone ffmpeg binary next to the app and shells out to it to encode replay exports (tango-pvp/src/replay/export.rs). This repo builds that binary for every platform Tango ships on, containing only the codecs/muxers/filters the exporter actually drives and nothing else (we start from --disable-everything and re-enable feature by feature).

It replaces the previously-bundled eugeneware/ffmpeg-static b6.0 builds, which carry the full kitchen-sink ffmpeg (~70 MB) when Tango uses a sliver of it.

Outputs

The build-ffmpeg workflow produces:

Artifact / release asset	Platform	Notes
ffmpeg-linux-x86_64	Linux x86_64	built on ubuntu-22.04 (glibc baseline)
ffmpeg-windows-x86_64.exe	Windows x86_64	MSVC toolchain, static CRT — needs no DLLs
ffmpeg-macos-arm64	macOS arm64	native, min macOS 11.0
ffmpeg-macos-x86_64	macOS x86_64	cross-compiled on the arm64 runner

The two macOS slices are shipped separately (not lipo'd here) because Tango's macos/build.sh already fat-binary's them itself.

The workflow is manual-only — start it from the Actions tab (Run workflow). It builds the latest FFmpeg release by default; set the ffmpeg_version input (e.g. 7.1.1) to pin a specific release.

Each run publishes its binaries (each with a .sha256) to a GitHub Release tagged ffmpeg-<version>. The workflow creates that tag/release itself — no tag push is involved — giving stable download URLs, e.g.:

https://github.com/<owner>/ffmpeg-build/releases/download/ffmpeg-8.1.1/ffmpeg-linux-x86_64

They're also attached to the run as plain Artifacts for quick debugging.

What's enabled, and why

Single source of truth: scripts/ffmpeg-config-common.sh. Every line is traced to a Tango code path:

Component	Tango usage
encoder libx264	scaled export — -c:v libx264 -vf scale=…,format=yuv420p
encoder libx264rgb	lossless export (scale = 0) — -c:v libx264rgb -qp 0
encoder aac	scaled-export audio — -c:a aac -b:a 384k
encoder flac	lossless-export audio — -c:a flac
decoders rawvideo, pcm_s16le	the raw RGBA / s16le streams piped from the emulator
demuxers rawvideo, pcm_s16le	-f rawvideo / -f s16le inputs
demuxer matroska	mux step reads back the intermediate .mkvs
muxer matroska	intermediates (-f matroska) + the final .mkv (lossless)
muxers mov/mp4	the final .mp4 (scaled export)
parsers h264, aac, flac	stream-copy mux (-c:v copy -c:a copy)
bsf extract_extradata	write avcC when copying H.264 into MP4
bsf aac_adtstoasc	AAC stream-copy safety
filters scale, format	nearest-neighbour upscale + pixel-format conversion
filters aresample/aformat/…	auto-inserted s16 → fltp etc. negotiation
protocols file, pipe	temp files + -i pipe:
external libx264 (GPL)	the H.264 encoders above (--enable-gpl)

The side-by-side ("twosided") export is composited in Rust and piped as one double-width rawvideo stream, so no hstack/overlay filter is needed.

Tango writes its per-stream intermediate temp files as matroska (-f matroska, see tango-pvp/src/replay/export.rs) and stream-copies them into the final container. Scaled exports produce an .mp4 (with -movflags +faststart); lossless exports (libx264rgb + FLAC, which mp4 only carries via experimental flags) produce an .mkv instead — the save dialog picks the extension to match.

The resulting binaries are GPL (because of x264).

Each build is smoke-tested (scripts/smoke-test.sh) by running Tango's exact command sequence — both encode paths, both audio codecs, and the flac-in-MP4 / h264-in-MP4 stream-copy mux — so a build missing any enabled component fails in CI rather than in a user's export.

Versions

Each run builds the latest FFmpeg release by default, resolved from the upstream git tags by scripts/latest-ffmpeg-version.sh. To build a specific release, set the ffmpeg_version workflow input. x264 tracks its stable branch (X264_REF); pin it to a commit SHA for fully reproducible builds.

Building locally

# Linux/macOS (needs nasm, pkg-config, a C compiler, curl, git).
# FFMPEG_VERSION unset -> builds the latest release; set it to pin.
export PREFIX="$PWD/prefix" OUTPUT="$PWD/out/ffmpeg"
./scripts/build-x264.sh
./scripts/build-ffmpeg.sh
./scripts/smoke-test.sh ./out/ffmpeg

Wiring Tango to these builds

Tango's packaging scripts currently download from eugeneware/ffmpeg-static. Point them at this repo's release assets instead — same URL shape, e.g. swap .../eugeneware/ffmpeg-static/releases/download/b6.0/ffmpeg-linux-x64 for .../<owner>/ffmpeg-build/releases/download/ffmpeg-<version>/ffmpeg-linux-x86_64:

• linux/build.sh — replace the ffmpeg-linux-x64 download with ffmpeg-linux-x86_64.
• win/build.sh — replace ffmpeg-win32-x64 with ffmpeg-windows-x86_64.exe.
• macos/build.sh — replace the two slices with ffmpeg-macos-arm64 and ffmpeg-macos-x86_64; its existing lipo step fat-binary's them as-is.

(Those edits live in the Tango repo, not here.)