story-studio/remotion/node_modules/mediabunny/dist/modules/shared/mp3-misc.js

/*!
 * 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/.
 */
export const FRAME_HEADER_SIZE = 4;
export const SAMPLING_RATES = [44100, 48000, 32000];
export const KILOBIT_RATES = [
    // lowSamplingFrequency === 0
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // layer = 0
    -1, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, -1, // layer 1
    -1, 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384, -1, // layer = 2
    -1, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448, -1, // layer = 3
    // lowSamplingFrequency === 1
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // layer = 0
    -1, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, -1, // layer = 1
    -1, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160, -1, // layer = 2
    -1, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256, -1, // layer = 3
];
/** 'Xing' */
export const XING = 0x58696e67;
/** 'Info' */
export const INFO = 0x496e666f;
export const computeMp3FrameSize = (lowSamplingFrequency, layer, bitrate, sampleRate, padding) => {
    if (layer === 0) {
        return 0; // Not expected that this is hit
    }
    else if (layer === 1) {
        return Math.floor(144 * bitrate / (sampleRate << lowSamplingFrequency)) + padding;
    }
    else if (layer === 2) {
        return Math.floor(144 * bitrate / sampleRate) + padding;
    }
    else { // layer === 3
        return (Math.floor(12 * bitrate / sampleRate) + padding) * 4;
    }
};
export const getXingOffset = (mpegVersionId, channel) => {
    return mpegVersionId === 3
        ? (channel === 3 ? 21 : 36)
        : (channel === 3 ? 13 : 21);
};
export const readMp3FrameHeader = (word, remainingBytes) => {
    const firstByte = word >>> 24;
    const secondByte = (word >>> 16) & 0xff;
    const thirdByte = (word >>> 8) & 0xff;
    const fourthByte = word & 0xff;
    if (firstByte !== 0xff && secondByte !== 0xff && thirdByte !== 0xff && fourthByte !== 0xff) {
        return {
            header: null,
            bytesAdvanced: 4,
        };
    }
    if (firstByte !== 0xff) {
        return { header: null, bytesAdvanced: 1 };
    }
    if ((secondByte & 0xe0) !== 0xe0) {
        return { header: null, bytesAdvanced: 1 };
    }
    let lowSamplingFrequency = 0;
    let mpeg25 = 0;
    if (secondByte & (1 << 4)) {
        lowSamplingFrequency = (secondByte & (1 << 3)) ? 0 : 1;
    }
    else {
        lowSamplingFrequency = 1;
        mpeg25 = 1;
    }
    const mpegVersionId = (secondByte >> 3) & 0x3;
    const layer = (secondByte >> 1) & 0x3;
    const bitrateIndex = (thirdByte >> 4) & 0xf;
    const frequencyIndex = ((thirdByte >> 2) & 0x3) % 3;
    const padding = (thirdByte >> 1) & 0x1;
    const channel = (fourthByte >> 6) & 0x3;
    const modeExtension = (fourthByte >> 4) & 0x3;
    const copyright = (fourthByte >> 3) & 0x1;
    const original = (fourthByte >> 2) & 0x1;
    const emphasis = fourthByte & 0x3;
    const kilobitRate = KILOBIT_RATES[lowSamplingFrequency * 16 * 4 + layer * 16 + bitrateIndex];
    if (kilobitRate === -1) {
        return { header: null, bytesAdvanced: 1 };
    }
    const bitrate = kilobitRate * 1000;
    const sampleRate = SAMPLING_RATES[frequencyIndex] >> (lowSamplingFrequency + mpeg25);
    const frameLength = computeMp3FrameSize(lowSamplingFrequency, layer, bitrate, sampleRate, padding);
    if (remainingBytes !== null && remainingBytes < frameLength) {
        // The frame doesn't fit into the rest of the file
        return { header: null, bytesAdvanced: 1 };
    }
    let audioSamplesInFrame;
    if (mpegVersionId === 3) {
        audioSamplesInFrame = layer === 3 ? 384 : 1152;
    }
    else {
        if (layer === 3) {
            audioSamplesInFrame = 384;
        }
        else if (layer === 2) {
            audioSamplesInFrame = 1152;
        }
        else {
            audioSamplesInFrame = 576;
        }
    }
    return {
        header: {
            totalSize: frameLength,
            mpegVersionId,
            layer,
            bitrate,
            frequencyIndex,
            sampleRate,
            channel,
            modeExtension,
            copyright,
            original,
            emphasis,
            audioSamplesInFrame,
        },
        bytesAdvanced: 1,
    };
};
export const encodeSynchsafe = (unsynchsafed) => {
    let mask = 0x7f;
    let synchsafed = 0;
    let unsynchsafedRest = unsynchsafed;
    while ((mask ^ 0x7fffffff) !== 0) {
        synchsafed = unsynchsafedRest & ~mask;
        synchsafed <<= 1;
        synchsafed |= unsynchsafedRest & mask;
        mask = ((mask + 1) << 8) - 1;
        unsynchsafedRest = synchsafed;
    }
    return synchsafed;
};
export const decodeSynchsafe = (synchsafed) => {
    let mask = 0x7f000000;
    let unsynchsafed = 0;
    while (mask !== 0) {
        unsynchsafed >>= 1;
        unsynchsafed |= synchsafed & mask;
        mask >>= 8;
    }
    return unsynchsafed;
};