mediabunny
Version:
Pure TypeScript media toolkit for reading, writing, and converting media files, directly in the browser.
64 lines (63 loc) • 2.25 kB
JavaScript
/*!
* Copyright (c) 2026-present, Vanilagy and contributors
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at https://mozilla.org/MPL/2.0/.
*/
import { Bitstream } from '../../shared/bitstream.js';
import { readBytes } from '../reader.js';
export const MIN_ADTS_FRAME_HEADER_SIZE = 7;
export const MAX_ADTS_FRAME_HEADER_SIZE = 9;
export const readAdtsFrameHeader = (slice) => {
// https://wiki.multimedia.cx/index.php/ADTS (last visited: 2025/08/17)
const startPos = slice.filePos;
const bytes = readBytes(slice, 9); // 9 with CRC, 7 without CRC
const bitstream = new Bitstream(bytes);
const syncword = bitstream.readBits(12);
if (syncword !== 0b1111_11111111) {
return null;
}
bitstream.skipBits(1); // MPEG version
const layer = bitstream.readBits(2);
if (layer !== 0) {
return null;
}
const protectionAbsence = bitstream.readBits(1);
const objectType = bitstream.readBits(2) + 1;
const samplingFrequencyIndex = bitstream.readBits(4);
if (samplingFrequencyIndex === 15) {
return null;
}
bitstream.skipBits(1); // Private bit
const channelConfiguration = bitstream.readBits(3);
if (channelConfiguration === 0) {
throw new Error('ADTS frames with channel configuration 0 are not supported.');
}
bitstream.skipBits(1); // Originality
bitstream.skipBits(1); // Home
bitstream.skipBits(1); // Copyright ID bit
bitstream.skipBits(1); // Copyright ID start
const frameLength = bitstream.readBits(13);
bitstream.skipBits(11); // Buffer fullness
const numberOfAacFrames = bitstream.readBits(2) + 1;
if (numberOfAacFrames !== 1) {
throw new Error('ADTS frames with more than one AAC frame are not supported.');
}
let crcCheck = null;
if (protectionAbsence === 1) { // No CRC
slice.filePos -= 2;
}
else { // CRC
crcCheck = bitstream.readBits(16);
}
return {
objectType,
samplingFrequencyIndex,
channelConfiguration,
frameLength,
numberOfAacFrames,
crcCheck,
startPos,
};
};