Skip to main content
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):
PathContent
/hls/master.m3u8HLS master playlist (one variant — AAC-LC 128 kbps)
/hls/audio.m3u8HLS media playlist (sliding window of recent segments)
/dash/manifest.mpdMPEG-DASH manifest (live profile, same segments)
/init.mp4fMP4 initialisation segment
/seg/{n}.m4sfMP4 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.