perf(transmuxer): various performance improvements (#6003)

This change improves loop performance - creating new arrays is not
performant in large loops, and a traditional for loop is more performant
than for .. of for large concatenations

---------

Co-authored-by: Ivan Kohut <ivan.kohut@lamin.ar>
Co-authored-by: Álvaro Velad Galván <ladvan91@hotmail.com>

Author: 3 people

lib/transmuxer/ts_transmuxer.js

@@ -705,7 +705,7 @@ shaka.transmuxer.TsTransmuxer = class {
     /** @type {?number} */
     let baseMediaDecodeTime = null;
 
-    let nalus = [];
+    const nalus = [];
     const videoData = tsParser.getVideoData();
     if (!videoData.length) {
       throw new shaka.util.Error(
@@ -716,7 +716,7 @@ shaka.transmuxer.TsTransmuxer = class {
     for (let i = 0; i < videoData.length; i++) {
       const pes = videoData[i];
       const dataNalus = pes.nalus;
-      nalus = nalus.concat(dataNalus);
+      nalus.push(...dataNalus);
       const frame = H264.parseFrame(dataNalus);
       if (!frame) {
         continue;
@@ -797,7 +797,7 @@ shaka.transmuxer.TsTransmuxer = class {
     /** @type {?number} */
     let baseMediaDecodeTime = null;
 
-    let nalus = [];
+    const nalus = [];
     const videoData = tsParser.getVideoData();
     if (!videoData.length) {
       throw new shaka.util.Error(
@@ -808,7 +808,7 @@ shaka.transmuxer.TsTransmuxer = class {
     for (let i = 0; i < videoData.length; i++) {
       const pes = videoData[i];
       const dataNalus = pes.nalus;
-      nalus = nalus.concat(dataNalus);
+      nalus.push(...dataNalus);
       const frame = H265.parseFrame(dataNalus);
       if (!frame) {
         continue;

lib/util/uint8array_utils.js

@@ -107,21 +107,26 @@ shaka.util.Uint8ArrayUtils = class {
    * @export
    */
   static concat(...varArgs) {
+    const BufferUtils = shaka.util.BufferUtils;
     let totalLength = 0;
-    for (const arr of varArgs) {
-      totalLength += arr.byteLength;
+    for (let i = 0; i < varArgs.length; ++i) {
+      const value = varArgs[i];
+      totalLength += value.byteLength;
     }
 
     const result = new Uint8Array(totalLength);
     let offset = 0;
-    for (const arr of varArgs) {
-      if (arr instanceof Uint8Array) {
-        result.set(arr, offset);
+
+    for (let i = 0; i < varArgs.length; ++i) {
+      const value = varArgs[i];
+      if (value instanceof Uint8Array) {
+        result.set(value, offset);
       } else {
-        result.set(shaka.util.BufferUtils.toUint8(arr), offset);
+        result.set(BufferUtils.toUint8(value), offset);
       }
-      offset += arr.byteLength;
+      offset += value.byteLength;
     }
+
     return result;
   }
 };