[YT seek] Only request header data and stop parsing header after reac…

…hing the desired cue

play-dl/YouTube/classes/SeekStream.ts

@@ -29,6 +29,10 @@ export class SeekStream {
      * Calculate per second bytes by using contentLength (Total bytes) / Duration (in seconds)
      */
     private per_sec_bytes: number;
+    /**
+     * Length of the header in bytes
+     */
+    private header_length: number;
     /**
      * Total length of audio file in bytes
      */
@@ -57,12 +61,20 @@ export class SeekStream {
      * @param url Audio Endpoint url.
      * @param type Type of Stream
      * @param duration Duration of audio playback [ in seconds ]
+     * @param headerLength Length of the header in bytes.
      * @param contentLength Total length of Audio file in bytes.
      * @param video_url YouTube video url.
      * @param options Options provided to stream function.
      */
-    constructor(url: string, duration: number, contentLength: number, video_url: string, options: StreamOptions) {
-        this.stream = new WebmSeeker({
+    constructor(
+        url: string,
+        duration: number,
+        headerLength: number,
+        contentLength: number,
+        video_url: string,
+        options: StreamOptions
+    ) {
+        this.stream = new WebmSeeker(options.seek!, {
             highWaterMark: 5 * 1000 * 1000,
             readableObjectMode: true
         });
@@ -72,6 +84,7 @@ export class SeekStream {
         this.bytes_count = 0;
         this.video_url = video_url;
         this.per_sec_bytes = Math.ceil(contentLength / duration);
+        this.header_length = headerLength;
         this.content_length = contentLength;
         this.request = null;
         this.timer = new Timer(() => {
@@ -82,21 +95,20 @@ export class SeekStream {
             this.timer.destroy();
             this.cleanup();
         });
-        this.seek(options.seek!);
+        this.seek();
     }
     /**
      * **INTERNAL Function**
      *
      * Uses stream functions to parse Webm Head and gets Offset byte to seek to.
-     * @param sec No of seconds to seek to
      * @returns Nothing
      */
-    private async seek(sec: number): Promise<void> {
+    private async seek(): Promise<void> {
         const parse = await new Promise(async (res, rej) => {
             if (!this.stream.headerparsed) {
                 const stream = await request_stream(this.url, {
                     headers: {
-                        range: `bytes=0-`
+                        range: `bytes=0-${this.header_length}`
                     }
                 }).catch((err: Error) => err);
 
@@ -111,6 +123,12 @@ export class SeekStream {
                 this.request = stream;
                 stream.pipe(this.stream, { end: false });
 
+                // headComplete should always be called, leaving this here just in case
+                stream.once('end', () => {
+                    this.stream.state = WebmSeekerState.READING_DATA;
+                    res('');
+                });
+
                 this.stream.once('headComplete', () => {
                     stream.unpipe(this.stream);
                     stream.destroy();
@@ -128,9 +146,9 @@ export class SeekStream {
         } else if (parse === 400) {
             await this.retry();
             this.timer.reuse();
-            return this.seek(sec);
+            return this.seek();
         }
-        const bytes = this.stream.seek(sec);
+        const bytes = this.stream.seek();
         if (bytes instanceof Error) {
             this.stream.emit('error', bytes);
             this.bytes_count = 0;

play-dl/YouTube/classes/WebmSeeker.ts

@@ -31,8 +31,11 @@ export class WebmSeeker extends Duplex {
     seekfound: boolean;
     private data_size: number;
     private data_length: number;
+    private sec: number;
+    private time: number;
+    private foundCue: boolean;
 
-    constructor(options: WebmSeekerOptions) {
+    constructor(sec: number, options: WebmSeekerOptions) {
         super(options);
         this.state = WebmSeekerState.READING_HEAD;
         this.cursor = 0;
@@ -42,6 +45,9 @@ export class WebmSeeker extends Duplex {
         this.seekfound = false;
         this.data_length = 0;
         this.data_size = 0;
+        this.sec = sec;
+        this.time = Math.floor(sec / 10) * 10;
+        this.foundCue = false;
     }
 
     private get vint_length(): number {
@@ -71,17 +77,16 @@ export class WebmSeeker extends Duplex {
 
     _read() {}
 
-    seek(sec: number): Error | number {
+    seek(): Error | number {
         let clusterlength = 0,
             position = 0;
-        const time = Math.floor(sec / 10) * 10;
-        let time_left = (sec - time) * 1000 || 0;
+        let time_left = (this.sec - this.time) * 1000 || 0;
         time_left = Math.round(time_left / 20) * 20;
         if (!this.header.segment.cues) return new Error('Failed to Parse Cues');
 
         for (let i = 0; i < this.header.segment.cues.length; i++) {
             const data = this.header.segment.cues[i];
-            if (Math.floor((data.time as number) / 1000) === time) {
+            if (Math.floor((data.time as number) / 1000) === this.time) {
                 position = data.position as number;
                 clusterlength = this.header.segment.cues[i + 1].position! - position - 1;
                 break;
@@ -130,18 +135,24 @@ export class WebmSeeker extends Duplex {
                 if (ebmlID.name === 'ebml') this.headfound = true;
                 else return new Error('Failed to find EBML ID at start of stream.');
             }
-            if (ebmlID.name === 'cluster') {
-                this.emit('headComplete');
-                this.cursor = this.chunk.length;
-                break;
-            }
             const data = this.chunk.slice(
                 this.cursor + this.data_size,
                 this.cursor + this.data_size + this.data_length
             );
             const parse = this.header.parse(ebmlID, data);
             if (parse instanceof Error) return parse;
 
+            // stop parsing the header once we have found the correct cue
+            if (ebmlID.name === 'cueClusterPosition') {
+                if (this.foundCue) {
+                    this.emit('headComplete');
+                    this.cursor = this.chunk.length;
+                    break;
+                } else if (this.time === (this.header.segment.cues!.at(-1)!.time as number) / 1000) {
+                    this.foundCue = true;
+                }
+            }
+
             if (ebmlID.type === DataType.master) {
                 this.cursor += this.data_size;
                 continue;

play-dl/YouTube/stream.ts

@@ -92,6 +92,7 @@ export async function stream_from_info(
             return new SeekStream(
                 final[0].url,
                 info.video_details.durationInSec,
+                final[0].indexRange.end,
                 Number(final[0].contentLength),
                 info.video_details.url,
                 options