mp3

func BitrateFor ¶ added in v0.6.6

func BitrateFor(sampleRate int) int

BitrateFor returns the CBR bitrate, in bits per second, the encoder uses for audio at sampleRate. Shine hard-codes 128 kbps, which is wrong on two counts for the low sample rates GopherTrunk records at:

• 128 kbps is not even a legal Layer-III bitrate for the MPEG-2.5 family (8/11.025/12 kHz), so Shine writes an out-of-range bitrate index that corrupts every frame header.
• More subtly, Shine's single-granule frames (every rate below 32 kHz) desync their bit-reservoir stuffing once the per-frame budget grows past roughly 3300 bits (~420 bytes/frame), emitting oversized frames that no demuxer can follow. This is why an 8 kHz call uploaded to Rdio Scanner transcodes to silence / "Invalid data found".

So each single-granule family gets the highest standard bitrate that keeps a frame comfortably under that limit — 32 kbps for MPEG-2.5, 64 kbps for MPEG-2 — both well above transparent for 8 kHz mono voice. The MPEG-1 rates (≥32 kHz) split each frame into two granules, halving the per-granule budget, so they keep Shine's 128 kbps default. Callers that pace a stream by bitrate (Icecast) use this so their timing tracks the real encoder output.

func Encode ¶

func Encode(samples []int16, sampleRate int) ([]byte, error)

Encode compresses mono 16-bit PCM sampled at sampleRate Hz into a complete MP3 byte stream. The input is treated as a single channel; callers with stereo audio must downmix first.

func EncodeWAVFile ¶

func EncodeWAVFile(path string) ([]byte, int, error)

EncodeWAVFile reads a 16-bit PCM mono WAV file from path and returns the equivalent MP3 byte stream plus the source sample rate.

func ReadWAV ¶

func ReadWAV(path string) ([]int16, int, error)

ReadWAV parses a canonical 16-bit PCM mono WAV file and returns its samples and sample rate. It tolerates extra chunks between `fmt ` and `data` (e.g. LIST/INFO) by walking the chunk list. Only mono 16-bit PCM is supported — the format the recorder writes.