65 lines
3 KiB
Markdown
65 lines
3 KiB
Markdown
# ECP-0033: Deterministic x264 + CMAF(fMP4) Segment Mode
|
|
|
|
## Summary
|
|
|
|
Add an optional stream mode that publishes HLS-compatible CMAF-style fragmented MP4 segments (`.m4s`) encoded with single-threaded `libx264` + AAC, alongside a separate init segment (`init.mp4`). The init segment is published on a dedicated MoQ side-track so subscribers can start playback without out-of-band files.
|
|
|
|
This is an incremental step toward a MoQ-native media pipeline while keeping browser playback practical via standard HLS fMP4 semantics.
|
|
|
|
## Goals
|
|
|
|
- Provide a "mature codec path" for experimentation: `libx264` + AAC.
|
|
- Make output more browser-friendly than raw MPEG-TS while staying simple.
|
|
- Preserve deterministic encoding constraints where feasible:
|
|
- single-threaded encoder
|
|
- `+bitexact` flags
|
|
- fixed GOP
|
|
- Keep the change reversible:
|
|
- default remains raw TS chunk publication
|
|
- CMAF mode is opt-in via CLI
|
|
|
|
## Non-Goals
|
|
|
|
- Full CMAF compliance validation across players.
|
|
- Multi-track audio language selection.
|
|
- End-to-end determinism across independent antennas (this requires timebase normalization and additional constraints).
|
|
- MoQ wire-level media standardization (that belongs in a later ECP).
|
|
|
|
## Design
|
|
|
|
- Publisher (`ec-node moq-publish`) adds `--encode {ts|cmaf}`.
|
|
- In `cmaf` mode:
|
|
- ingest bytes from the source (TS file/HDHR/iptv adapter)
|
|
- invoke `ffmpeg` to encode and segment to HLS fMP4:
|
|
- writes `init.mp4` and `segment_%06d.m4s`
|
|
- publish:
|
|
- `init.mp4` as a single MoQ object on `--init-track` (default: `init`)
|
|
- `.m4s` segments as MoQ objects on the main track
|
|
- all MoQ tracks (objects, init, manifests) are created before the broadcast is published
|
|
to avoid implementation quirks where late-added tracks are not deliverable
|
|
- manifests remain per-epoch over the segment objects only (init is out-of-manifest for now)
|
|
- Subscriber (`ec-node moq-subscribe`) adds:
|
|
- `--container {ts|cmaf}`
|
|
- `--subscribe-init` to fetch `init.mp4` from `--init-track`
|
|
- local output becomes:
|
|
- `index.m3u8` with `#EXT-X-MAP:URI="init.mp4"`
|
|
- `init.mp4`
|
|
- rolling window of `segment_*.m4s`
|
|
|
|
## Rationale
|
|
|
|
- fMP4 (CMAF-style) is broadly supported by modern HLS implementations and aligns with future MoQ media layouts.
|
|
- `libx264` is stable and widely available, making it a pragmatic baseline for determinism experiments.
|
|
- Publishing init as a side-track avoids special cases in the primary segment stream and keeps the UI/receiver model "a stream is a stream".
|
|
|
|
## Risks
|
|
|
|
- MP4 muxers can embed non-deterministic metadata (timestamps/brands). We mitigate by:
|
|
- `+bitexact` flags and single-threaded encoding
|
|
- stripping container metadata where feasible (future follow-up may be needed)
|
|
- Segment boundaries are time-based and depend on timestamps/keyframes; cross-antenna byte equality is not guaranteed yet.
|
|
|
|
## Rollout
|
|
|
|
- Land CMAF mode behind `--encode cmaf` and `--container cmaf`.
|
|
- Add an ignored HDHomeRun E2E test that exercises split-source mesh in CMAF mode.
|