> ## Documentation Index
> Fetch the complete documentation index at: https://rockboxzig.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# 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](/quickstart): the web
UI's `<audio>` element attaches to the HLS stream automatically as soon as the
active output is set to `cmaf` / `hls` / `dash`.

```toml theme={"theme":{"light":"catppuccin-latte","dark":"min-dark"}}
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

```sh theme={"theme":{"light":"catppuccin-latte","dark":"min-dark"}}
# 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:

```toml theme={"theme":{"light":"catppuccin-latte","dark":"min-dark"}}
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:

```nginx theme={"theme":{"light":"catppuccin-latte","dark":"min-dark"}}
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:

```graphql theme={"theme":{"light":"catppuccin-latte","dark":"min-dark"}}
mutation { connectDevice(id: "<device-id>") }
```

…or pick another output from the web UI's device picker. See
[Audio output › Overview](/audio-output/overview).