Title: MP3 Playback
Description: Play MP3 files over GhostLink using the Audio app
URL: /latest/audio/playback/
Version: latest
Section: Audio
Search index: /search-index.json

# MP3 Playback

> Play MP3 files over GhostLink using the Audio app

## On this page

- [Requirements](#requirements)
- [File Setup](#file-setup)
- [Opening the App](#opening-the-app)
- [Controls](#controls)
- [Playback Behavior](#playback-behavior)
- [GhostLink Commands](#ghostlink-commands)
- [Troubleshooting](#troubleshooting)

---

The Audio app plays MP3 files stored on the SD card and streams them over GhostLink between the two chips in The Banshee.
## Requirements
- The Banshee hardware. Its two-chip audio setup uses the Banshee_C5 and Banshee_S3 builds.
- A GhostLink connection between the Banshee control/display chip and audio receiver chip.
- MP3 files on the SD card in /mnt/ghostesp/audio.
- MP3 bitrate under 264kbps. Higher bitrate files are rejected with an on-device toast.
- For headphone output, the TLV320DAC3100 route is detected once before playback starts.
## File Setup
Create this folder on the SD card:
/mnt/ghostesp/audio
Copy .mp3 files into that folder. The Audio app scans the folder when it opens and lists the tracks alphabetically.
Recommended encoding:
- MP3, constant bitrate when possible.
- 128kbps or 160kbps for best reliability.
- Under 264kbps; 264kbps and higher is not accepted.
- Standard sample rates such as 44.1kHz.
## Opening the App
On the device UI, open:
Apps → Audio
If no MP3 files are found, the app shows a toast asking for files in /mnt/ghostesp/audio.
## Controls
- Tap a track row to start playback.
- Use previous/next to switch tracks.
- Use play/pause to pause or resume playback.
- Encoder rotation adjusts volume on supported hardware.
- Touch-drag inside the track list scrolls the list.
The currently selected row is marked SEL. The active track is marked PLAY; paused playback is marked PAUSE.
## Playback Behavior
Audio data is sent over GhostLink as a paced stream. The receiver reports its audio buffer fill level and playback time back to the sender so the stream can adapt to real receiver conditions.
The app displays:
- Current track name.
- Elapsed and estimated total time.
- Playback state.
- Detected bitrate.
- Receiver buffer percentage when feedback is available.
- Volume percentage.
Pause is immediate: the receiver discards buffered audio and resets output so it does not continue playing through the queued buffer.
## GhostLink Commands
These commands are used internally by the Audio app and can be useful for debugging:
audio start
audio stop
audio pause
audio flush
audio state <fill_bytes> <capacity_bytes> <played_ms>
audio state is sent by the receiver to report buffer fill and playback clock. The sender uses it for progress display and adaptive pacing.
## Troubleshooting
- Audio app is missing: Audio playback is currently Banshee-only. Make sure both Banshee chips are flashed with the correct paired builds.
- No files shown: Check that the SD card contains .mp3 files in /mnt/ghostesp/audio.
- Bitrate toast appears: Re-encode the file below 264kbps; 128kbps or 160kbps is recommended.
- Playback underruns or stutters: Try a lower bitrate file and confirm GhostLink is connected with no other streaming app active.
- No headphone output: Reconnect headphones before starting playback so one-shot route detection can select the right output path.
- Progress looks wrong: Some VBR files do not expose accurate duration data. CBR files produce more stable estimates.