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Viewing file:     FLACParser.js (5.06 KB)      -rw-r--r--

/* Copyright 2020-2023 Ethan Halsall
    
    This file is part of codec-parser.
    
    codec-parser is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    codec-parser is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <https://www.gnu.org/licenses/>
*/

import { frameStore, headerStore } from "../../globals.js";
import {
  length,
  pageSequenceNumber,
  data,
  codec,
  codecFrames,
  segments,
  subarray,
  readRawData,
  incrementRawData,
  mapFrameStats,
  logWarning,
  parseFrame,
  parseOggPage,
  getHeader,
  enable,
  checkFrameFooterCrc16,
  getHeaderFromUint8Array,
} from "../../constants.js";
import Parser from "../Parser.js";
import FLACFrame from "./FLACFrame.js";
import FLACHeader from "./FLACHeader.js";

const MIN_FLAC_FRAME_SIZE = 2;
const MAX_FLAC_FRAME_SIZE = 512 * 1024;

export default class FLACParser extends Parser {
  constructor(codecParser, headerCache, onCodec) {
    super(codecParser, headerCache);
    this.Frame = FLACFrame;
    this.Header = FLACHeader;

    onCodec(this[codec]);
  }

  get [codec]() {
    return "flac";
  }

  *_getNextFrameSyncOffset(offset) {
    const data = yield* this._codecParser[readRawData](2, 0);
    const dataLength = data[length] - 2;

    while (offset < dataLength) {
      // * `11111111|111110..`: Frame sync
      // * `........|......0.`: Reserved 0 - mandatory, 1 - reserved
      const firstByte = data[offset];
      if (firstByte === 0xff) {
        const secondByte = data[offset + 1];
        if (secondByte === 0xf8 || secondByte === 0xf9) break;
        if (secondByte !== 0xff) offset++; // might as well check for the next sync byte
      }
      offset++;
    }

    return offset;
  }

  *[parseFrame]() {
    // find the first valid frame header
    do {
      const header = yield* FLACHeader[getHeader](
        this._codecParser,
        this._headerCache,
        0,
      );

      if (header) {
        // found a valid frame header
        // find the next valid frame header
        let nextHeaderOffset =
          headerStore.get(header)[length] + MIN_FLAC_FRAME_SIZE;

        while (nextHeaderOffset <= MAX_FLAC_FRAME_SIZE) {
          if (
            this._codecParser._flushing ||
            (yield* FLACHeader[getHeader](
              this._codecParser,
              this._headerCache,
              nextHeaderOffset,
            ))
          ) {
            // found a valid next frame header
            let frameData = yield* this._codecParser[readRawData](
              nextHeaderOffset,
            );

            if (!this._codecParser._flushing)
              frameData = frameData[subarray](0, nextHeaderOffset);

            // check that this is actually the next header by validating the frame footer crc16
            if (FLACFrame[checkFrameFooterCrc16](frameData)) {
              // both frame headers, and frame footer crc16 are valid, we are synced (odds are pretty low of a false positive)
              const frame = new FLACFrame(frameData, header);

              this._headerCache[enable](); // start caching when synced
              this._codecParser[incrementRawData](nextHeaderOffset); // increment to the next frame
              this._codecParser[mapFrameStats](frame);

              return frame;
            }
          }

          nextHeaderOffset = yield* this._getNextFrameSyncOffset(
            nextHeaderOffset + 1,
          );
        }

        this._codecParser[logWarning](
          `Unable to sync FLAC frame after searching ${nextHeaderOffset} bytes.`,
        );
        this._codecParser[incrementRawData](nextHeaderOffset);
      } else {
        // not synced, increment data to continue syncing
        this._codecParser[incrementRawData](
          yield* this._getNextFrameSyncOffset(1),
        );
      }
    } while (true);
  }

  [parseOggPage](oggPage) {
    if (oggPage[pageSequenceNumber] === 0) {
      // Identification header

      this._headerCache[enable]();
      this._streamInfo = oggPage[data][subarray](13);
    } else if (oggPage[pageSequenceNumber] === 1) {
      // Vorbis comments
    } else {
      oggPage[codecFrames] = frameStore
        .get(oggPage)
        [segments].map((segment) => {
          const header = FLACHeader[getHeaderFromUint8Array](
            segment,
            this._headerCache,
          );

          if (header) {
            return new FLACFrame(segment, header, this._streamInfo);
          } else {
            this._codecParser[logWarning](
              "Failed to parse Ogg FLAC frame",
              "Skipping invalid FLAC frame",
            );
          }
        })
        .filter((frame) => !!frame);
    }

    return oggPage;
  }
}