mediabunny
Version:
Pure TypeScript media toolkit for reading, writing, and converting media files, directly in the browser.
70 lines (69 loc) • 1.99 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/.
*/
export class Bitstream {
constructor(bytes) {
this.bytes = bytes;
/** Current offset in bits. */
this.pos = 0;
}
seekToByte(byteOffset) {
this.pos = 8 * byteOffset;
}
readBit() {
const byteIndex = Math.floor(this.pos / 8);
const byte = this.bytes[byteIndex] ?? 0;
const bitIndex = 0b111 - (this.pos & 0b111);
const bit = (byte & (1 << bitIndex)) >> bitIndex;
this.pos++;
return bit;
}
readBits(n) {
if (n === 1) {
return this.readBit();
}
let result = 0;
for (let i = 0; i < n; i++) {
result <<= 1;
result |= this.readBit();
}
return result;
}
writeBits(n, value) {
const end = this.pos + n;
for (let i = this.pos; i < end; i++) {
const byteIndex = Math.floor(i / 8);
let byte = this.bytes[byteIndex];
const bitIndex = 0b111 - (i & 0b111);
byte &= ~(1 << bitIndex);
byte |= ((value & (1 << (end - i - 1))) >> (end - i - 1)) << bitIndex;
this.bytes[byteIndex] = byte;
}
this.pos = end;
}
;
readAlignedByte() {
if (this.pos % 8 !== 0) {
throw new Error('Bitstream is not byte-aligned.');
}
const byteIndex = this.pos / 8;
const byte = this.bytes[byteIndex] ?? 0;
this.pos += 8;
return byte;
}
skipBits(n) {
this.pos += n;
}
getBitsLeft() {
return this.bytes.length * 8 - this.pos;
}
clone() {
const clone = new Bitstream(this.bytes);
clone.pos = this.pos;
return clone;
}
}