fix: Avoid useless MSE reset when transmuxing muxed content (#7818)

Author: avelad

lib/media/media_source_engine.js

@@ -2247,32 +2247,32 @@ shaka.media.MediaSourceEngine = class {
   }
 
   /**
-   * Codec switch if necessary, this will not resolve until the codec
-   * switch is over.
    * @param {shaka.util.ManifestParserUtils.ContentType} contentType
    * @param {string} mimeType
    * @param {string} codecs
-   * @param {!Map.<shaka.util.ManifestParserUtils.ContentType,
-   *               shaka.extern.Stream>} streamsByType
-   * @return {!Promise.<boolean>} true if there was a codec switch,
-   *                              false otherwise.
+   * @return {{transmuxer: ?shaka.extern.Transmuxer,
+   *          transmuxerMuxed: boolean, basicType: string, codec: string,
+   *          mimeType: string}}
    * @private
    */
-  async codecSwitchIfNecessary_(contentType, mimeType, codecs, streamsByType) {
+  getRealInfo_(contentType, mimeType, codecs) {
     const ContentType = shaka.util.ManifestParserUtils.ContentType;
-    if (contentType == ContentType.TEXT) {
-      return false;
-    }
     const MimeUtils = shaka.util.MimeUtils;
-    const currentCodec = MimeUtils.getNormalizedCodec(
-        MimeUtils.getCodecs(this.sourceBufferTypes_[contentType]));
-    const currentBasicType = MimeUtils.getBasicType(
-        this.sourceBufferTypes_[contentType]);
-
     /** @type {?shaka.extern.Transmuxer} */
     let transmuxer;
     let transmuxerMuxed = false;
-    let newMimeType = shaka.util.MimeUtils.getFullType(mimeType, codecs);
+    const audioCodec = shaka.util.ManifestParserUtils.guessCodecsSafe(
+        ContentType.AUDIO, (codecs || '').split(','));
+    const videoCodec = shaka.util.ManifestParserUtils.guessCodecsSafe(
+        ContentType.VIDEO, (codecs || '').split(','));
+    let codec = videoCodec;
+    if (contentType == ContentType.AUDIO) {
+      codec = audioCodec;
+    }
+    if (!codec) {
+      codec = codecs;
+    }
+    let newMimeType = shaka.util.MimeUtils.getFullType(mimeType, codec);
     let needTransmux = this.config_.forceTransmux;
     if (!shaka.media.Capabilities.isTypeSupported(newMimeType) ||
         (!this.sequenceMode_ &&
@@ -2282,36 +2282,79 @@ shaka.media.MediaSourceEngine = class {
     const TransmuxerEngine = shaka.transmuxer.TransmuxerEngine;
     if (needTransmux) {
       const newMimeTypeWithAllCodecs =
-          shaka.util.MimeUtils.getFullTypeWithAllCodecs(mimeType, codecs);
+          shaka.util.MimeUtils.getFullTypeWithAllCodecs(mimeType, codec);
       const transmuxerPlugin =
           TransmuxerEngine.findTransmuxer(newMimeTypeWithAllCodecs);
       if (transmuxerPlugin) {
         transmuxer = transmuxerPlugin();
-        const audioCodec = shaka.util.ManifestParserUtils.guessCodecsSafe(
-            ContentType.AUDIO, (codecs || '').split(','));
-        const videoCodec = shaka.util.ManifestParserUtils.guessCodecsSafe(
-            ContentType.VIDEO, (codecs || '').split(','));
         if (audioCodec && videoCodec) {
           transmuxerMuxed = true;
-          let codec = videoCodec;
-          if (contentType == ContentType.AUDIO) {
-            codec = audioCodec;
-          }
-          newMimeType = transmuxer.convertCodecs(contentType,
-              shaka.util.MimeUtils.getFullTypeWithAllCodecs(mimeType, codec));
-        } else {
-          newMimeType =
-              transmuxer.convertCodecs(contentType, newMimeTypeWithAllCodecs);
         }
+        newMimeType =
+            transmuxer.convertCodecs(contentType, newMimeTypeWithAllCodecs);
       }
     }
 
     const newCodec = MimeUtils.getNormalizedCodec(
         MimeUtils.getCodecs(newMimeType));
     const newBasicType = MimeUtils.getBasicType(newMimeType);
+    return {
+      transmuxer,
+      transmuxerMuxed,
+      basicType: newBasicType,
+      codec: newCodec,
+      mimeType: newMimeType,
+    };
+  }
+
+  /**
+   * Codec switch if necessary, this will not resolve until the codec
+   * switch is over.
+   * @param {shaka.util.ManifestParserUtils.ContentType} contentType
+   * @param {string} mimeType
+   * @param {string} codecs
+   * @param {!Map.<shaka.util.ManifestParserUtils.ContentType,
+   *               shaka.extern.Stream>} streamsByType
+   * @return {!Promise.<boolean>} true if there was a codec switch,
+   *                              false otherwise.
+   * @private
+   */
+  async codecSwitchIfNecessary_(contentType, mimeType, codecs, streamsByType) {
+    const ContentType = shaka.util.ManifestParserUtils.ContentType;
+    if (contentType == ContentType.TEXT) {
+      return false;
+    }
+    const MimeUtils = shaka.util.MimeUtils;
+    const currentCodec = MimeUtils.getNormalizedCodec(
+        MimeUtils.getCodecs(this.sourceBufferTypes_[contentType]));
+    const currentBasicType = MimeUtils.getBasicType(
+        this.sourceBufferTypes_[contentType]);
+
+    const realInfo = this.getRealInfo_(contentType, mimeType, codecs);
+    const transmuxer = realInfo.transmuxer;
+    const transmuxerMuxed = realInfo.transmuxerMuxed;
+    const newBasicType = realInfo.basicType;
+    const newCodec = realInfo.codec;
+    const newMimeType = realInfo.mimeType;
+
+    let muxedContentCheck = true;
+    if (transmuxerMuxed) {
+      const muxedRealInfo =
+          this.getRealInfo_(ContentType.AUDIO, mimeType, codecs);
+      const muxedCurrentCodec = MimeUtils.getNormalizedCodec(
+          MimeUtils.getCodecs(this.sourceBufferTypes_[ContentType.AUDIO]));
+      const muxedCurrentBasicType = MimeUtils.getBasicType(
+          this.sourceBufferTypes_[ContentType.AUDIO]);
+      muxedContentCheck = muxedCurrentCodec == muxedRealInfo.codec &&
+        muxedCurrentBasicType == muxedRealInfo.basicType;
+      if (muxedRealInfo.transmuxer) {
+        muxedRealInfo.transmuxer.destroy();
+      }
+    }
 
     // Current/new codecs base and basic type match then no need to switch
-    if (currentCodec === newCodec && currentBasicType === newBasicType) {
+    if (currentCodec === newCodec && currentBasicType === newBasicType &&
+        muxedContentCheck) {
       if (this.transmuxers_[contentType] && !transmuxer) {
         this.transmuxers_[contentType].destroy();
         delete this.transmuxers_[contentType];

test/transmuxer/transmuxer_integration.js

@@ -383,12 +383,7 @@ describe('Transmuxer Player', () => {
 
       // eslint-disable-next-line max-len
       await player.load('/base/test/test/assets/hls-ts-muxed-mp3-h264/index.m3u8');
-      try {
-        await video.play();
-      // eslint-disable-next-line no-restricted-syntax
-      } catch (e) {
-        // Ignore play errors
-      }
+      await video.play();
       expect(player.isLive()).toBe(false);
 
       // Wait for the video to start playback.  If it takes longer than 10