ezaudio

Audio for Bend 2.

Install

With Bend alone there is nothing to install: import ezaudio by its hub name and bend fetches it from the hub into ~/.bend/lib on the first run. 0x05eb91b04a37c34a9abe2324661894f5 is ezaudio v0.2.9.

import 0x05eb91b04a37c34a9abe2324661894f5/main.bend as Au

Or with ez, which records the package in ez.toml (ez init makes one):

ez add Emerging-Patterns/ezaudio

Usage

A clip is a Clip: a sample rate, a channel count, a sample format, and interleaved frames. s16 is signed 16-bit PCM. f32 is IEEE 754 binary32, stored as its bits. decode_wav and encode_wav read and write a RIFF WAVE file of that PCM. decode_mp3 reads MPEG-1 Layer III into f32 frames. encode_mp3 writes MPEG-1 Layer III at 320 kbit/s. One mono signed-16 sample whose magnitude is 1..15 is stored as a single Huffman pair; decoding that frame returns the two magnitudes and then zeros. Other clips are encoded with the filterbank. count, fill, trim, and concat are the raw-frame helpers. Resampling is not in this version.

import 0x05eb91b04a37c34a9abe2324661894f5/main.bend as Au

def main() -> U32:
  Au.rate(Au.clip(8000, 1, Au.s16(), [0, 1]))

Compliance

Closed equalities in ezaudio/LAWS.bend, proved in ezaudio/PROOF.bend (bend ezaudio/PROOF.bend), target:

• The IBM/Microsoft RIFF WAVE form: the RIFF, WAVE, fmt , and data identifiers. A mono signed-16 clip at 8000 Hz encodes as PCM (format tag 1), one channel, 16 bits, little-endian samples, and decodes back to that clip. Stereo signed-16, and mono and stereo IEEE 754 binary32 (format tag 3), round-trip the same way, including the bits of 1.0. A byte list that is not RIFF, an empty frame list, and a zero sample rate encode or decode as none.
• trim keeps a span of frames, including the whole clip, and is none past the end. concat appends clips that share rate, channels, and format, and is none when they differ.
• ISO/IEC 11172-3 MPEG-1 Layer III: the header FF FB 90 C0 is Layer III, MPEG-1, 128 kbit/s, 44100 Hz, single channel. Layer I and Layer II decode as none, as do joint stereo, a CRC, and a header with no frame behind it. A silent frame at 320 kbit/s is the header and then zeros for the rest of 1152 * 320 * 125 / hz bytes: FF FB E0 C4 and 1044 bytes at 44100 Hz mono, FF FB E0 04 and 1044 bytes for stereo, FF FB E4 C4 and 960 bytes at 48000 Hz, FF FB E8 C4 and 1440 bytes at 32000 Hz. Decoding those byte strings yields 1152 zero binary32 samples per channel. Binary32 silence encodes as the mono frame. One mono signed-16 sample of magnitude 1 encodes with the same header and length. Its first granule is a long block, big_values 1, global_gain 0, part2_3_length 4, Huffman table 13. The second granule's big_values is 0. Decoding that frame returns the Huffman pair as the first two words (1, then 0) and 1150 zeros. That equality is the pair, not the synthesis filterbank. An empty sample list, and a rate other than 32000, 44100, or 48000, encode as none.

Decode accepts long blocks only. Short blocks, a non-zero scale-factor compress, a bit reservoir, joint stereo, a CRC, the count1 region, preflag, and scale-factor scale are none. Full codec conformance is not claimed yet.