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

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+/*!
+ * 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;
+};