Merge pull request #1943 from DolbyLaboratories:dlb/ac4-ajoc/dev

PiperOrigin-RevId: 702281314
(cherry picked from commit e499377)

libraries/extractor/src/main/java/androidx/media3/extractor/Ac4Util.java

@@ -410,13 +410,22 @@ public static Format parseAc4AnnexEFormat(
               ac4Presentation.hasBackChannels,
               ac4Presentation.topChannelPairs);
     } else {
-      channelCount = ac4Presentation.numOfUmxObjects;
+      // The ETSI TS 103 190-2 V1.2.1 (2018-02) specification defines the parameter
+      // n_umx_objects_minus1 in Annex E (E.11.11) to specify the number of fullband objects. While
+      // the elementary stream specification (section 6.3.2.8.1 and 6.3.2.10.4) provides information
+      // about the presence of an LFE channel within the set of dynamic objects, this detail is not
+      // explicitly stated in the ISO Base Media File Format (Annex E). However, current
+      // implementation practices consistently include the LFE channel when creating an object-based
+      // substream. As a result, it has been decided that when interpreting the ISO Base Media File
+      // Format, the LFE channel should always be counted as part of the total channel count.
+      int lfeChannelCount = 1;
+      channelCount = ac4Presentation.numOfUmxObjects + lfeChannelCount;
       // TODO: There is a bug in ETSI TS 103 190-2 V1.2.1 (2018-02), E.11.11
       // For AC-4 level 4 stream, the intention is to set 19 to n_umx_objects_minus1 but it is
       // equal to 15 based on current specification. Dolby has filed a bug report to ETSI.
       // The following sentence should be deleted after ETSI specification error is fixed.
       if (ac4Presentation.level == 4) {
-        channelCount = channelCount == 16 ? 21 : channelCount;
+        channelCount = channelCount == 17 ? 21 : channelCount;
       }
     }