Initial commit

node_modules/prism-media/src/opus/OggDemuxer.js

@@ -0,0 +1,118 @@
+const { Transform } = require('stream');
+
+const OGG_PAGE_HEADER_SIZE = 26;
+const STREAM_STRUCTURE_VERSION = 0;
+
+const charCode = x => x.charCodeAt(0);
+const OGGS_HEADER = Buffer.from([...'OggS'].map(charCode));
+const OPUS_HEAD = Buffer.from([...'OpusHead'].map(charCode));
+const OPUS_TAGS = Buffer.from([...'OpusTags'].map(charCode));
+
+/**
+ * Demuxes an Ogg stream (containing Opus audio) to output an Opus stream.
+ * @extends {TransformStream}
+ * @memberof opus
+ */
+class OggDemuxer extends Transform {
+  /**
+   * Creates a new OggOpus demuxer.
+   * @param {Object} [options] options that you would pass to a regular Transform stream.
+   * @memberof opus
+   */
+  constructor(options = {}) {
+    super(Object.assign({ readableObjectMode: true }, options));
+    this._remainder = null;
+    this._head = null;
+    this._bitstream = null;
+  }
+
+  _transform(chunk, encoding, done) {
+    if (this._remainder) {
+      chunk = Buffer.concat([this._remainder, chunk]);
+      this._remainder = null;
+    }
+
+    while (chunk) {
+      const result = this._readPage(chunk);
+      if (result) chunk = result;
+      else break;
+    }
+    this._remainder = chunk;
+    done();
+  }
+
+  /**
+   * Reads a page from a buffer
+   * @private
+   * @param {Buffer} chunk the chunk containing the page
+   * @returns {boolean|Buffer} if a buffer, it will be a slice of the excess data of the original, otherwise it will be
+   * false and would indicate that there is not enough data to go ahead with reading this page.
+   */
+  _readPage(chunk) {
+    if (chunk.length < OGG_PAGE_HEADER_SIZE) {
+      return false;
+    }
+    if (!chunk.slice(0, 4).equals(OGGS_HEADER)) {
+      throw Error(`capture_pattern is not ${OGGS_HEADER}`);
+    }
+    if (chunk.readUInt8(4) !== STREAM_STRUCTURE_VERSION) {
+      throw Error(`stream_structure_version is not ${STREAM_STRUCTURE_VERSION}`);
+    }
+
+    if (chunk.length < 27) return false;
+    const pageSegments = chunk.readUInt8(26);
+    if (chunk.length < 27 + pageSegments) return false;
+    const table = chunk.slice(27, 27 + pageSegments);
+    const bitstream = chunk.readUInt32BE(14);
+
+    let sizes = [], totalSize = 0;
+
+    for (let i = 0; i < pageSegments;) {
+      let size = 0, x = 255;
+      while (x === 255) {
+        if (i >= table.length) return false;
+        x = table.readUInt8(i);
+        i++;
+        size += x;
+      }
+      sizes.push(size);
+      totalSize += size;
+    }
+
+    if (chunk.length < 27 + pageSegments + totalSize) return false;
+
+    let start = 27 + pageSegments;
+    for (const size of sizes) {
+      const segment = chunk.slice(start, start + size);
+      const header = segment.slice(0, 8);
+      if (this._head) {
+        if (header.equals(OPUS_TAGS)) this.emit('tags', segment);
+        else if (this._bitstream === bitstream) this.push(segment);
+      } else if (header.equals(OPUS_HEAD)) {
+        this.emit('head', segment);
+        this._head = segment;
+        this._bitstream = bitstream;
+      } else {
+        this.emit('unknownSegment', segment);
+      }
+      start += size;
+    }
+    return chunk.slice(start);
+  }
+}
+
+/**
+ * Emitted when the demuxer encounters the opus head.
+ * @event OggDemuxer#head
+ * @memberof opus
+ * @param {Buffer} segment a buffer containing the opus head data.
+ */
+
+/**
+ * Emitted when the demuxer encounters opus tags.
+ * @event OggDemuxer#tags
+ * @memberof opus
+ * @param {Buffer} segment a buffer containing the opus tags.
+ */
+
+module.exports = OggDemuxer;