HLS + MPEG-DASH (CMAF)

Live AAC-LC stream in fragmented MP4 — plays directly in any browser.

The CMAF sink encodes live audio as AAC-LC in a fragmented MP4 container and serves it as both HLS and MPEG-DASH from the same in-memory segment ring buffer. Any HLS- or DASH-capable client can play the stream — including every modern browser — without installing extra software.

This is the default audio output for the Docker image: the web UI’s <audio> element attaches to the HLS stream automatically as soon as the active output is set to cmaf / hls / dash.

music_dir       = "/path/to/Music"
audio_output    = "cmaf"          # also accepts "hls" or "dash"
cmaf_http_port  = 7882            # optional, default 7882
cmaf_bitrate    = 128000          # optional, AAC-LC bitrate in bps

Endpoints

Once rockboxd is running with audio_output = "cmaf", three endpoints are served on cmaf_http_port (default 7882):

Path	Content
/hls/master.m3u8	HLS master playlist (one variant — AAC-LC 128 kbps)
/hls/audio.m3u8	HLS media playlist (sliding window of recent segments)
/dash/manifest.mpd	MPEG-DASH manifest (live profile, same segments)
/init.mp4	fMP4 initialisation segment
/seg/{n}.m4s	fMP4 media segments (~2 s each)

Play from anywhere

# Browser — open the web UI; <audio> attaches automatically.
open http://localhost:6062

# CLI players
ffplay http://localhost:7882/hls/master.m3u8
vlc    http://localhost:7882/hls/master.m3u8
mpv    http://localhost:7882/hls/master.m3u8

# Or stream the DASH manifest
ffplay http://localhost:7882/dash/manifest.mpd

How it works

Rockbox PCM (S16LE / 44.1 kHz / stereo)
  → fdk-aac (AAC-LC, 1024-sample frames)
    → fMP4 segmenter (86 frames ≈ 2 s per segment)
      → SegmentStore (sliding ring, last ~6 segments in memory)
        → HTTP server (/init.mp4, /seg/{n}.m4s, /hls/*.m3u8, /dash/manifest.mpd)

• A 2-second sliding window of segments is retained; clients always join at the live edge.
• Between tracks the encoder emits silence segments at wall-clock cadence so clients don’t see an empty playlist (which hls.js would treat as a fatal levelEmptyError).
• The bitrate is clamped to 32 000 – 320 000 bps. Outside that range it is silently clamped to the nearest endpoint.

Mirror to disk for an external HTTP server

To serve the same artefacts from nginx, Caddy, or a CDN origin, point the sink at a directory:

audio_output     = "cmaf"
cmaf_segment_dir = "/var/www/rockbox-cmaf"

init.mp4, seg/N.m4s, hls/master.m3u8, hls/audio.m3u8, and dash/manifest.mpd are all written there alongside the in-memory ring. The in-memory ring is always authoritative; disk I/O is best-effort and never blocks encoding.

Example nginx vhost:

server {
    listen 80;
    location / {
        root /var/www/rockbox-cmaf;
        add_header Cache-Control "no-cache";
        add_header Access-Control-Allow-Origin "*";
    }
}

Licensing note

libfdk-aac ships under the Software License for The Fraunhofer FDK AAC Codec Library for Android — open source but not GPL-compatible. Redistributing a binary that combines this sink with the GPLv2 Rockbox firmware is a license conflict for redistribution. Personal / non-distributed use is the intended scope.

Switching to another sink

Edit audio_output in settings.toml and restart, or call:

mutation { connectDevice(id: "<device-id>") }

…or pick another output from the web UI’s device picker. See Audio output › Overview.