Enable Passthrough remixer for more than 2 audio channels (#209)

* Enable Passthrough remixer for more than 2 channels

* Remove audio track strategy in issue75 tests

Author: natario1

.idea/misc.xml

@@ -14,6 +14,7 @@ import com.otaliastudios.transcoder.source.AssetFileDescriptorDataSource
 import com.otaliastudios.transcoder.source.BlankAudioDataSource
 import com.otaliastudios.transcoder.source.ClipDataSource
 import com.otaliastudios.transcoder.source.FileDescriptorDataSource
+import com.otaliastudios.transcoder.strategy.DefaultAudioStrategy
 import com.otaliastudios.transcoder.strategy.DefaultVideoStrategy
 import com.otaliastudios.transcoder.validator.WriteAlwaysValidator
 import org.junit.Assume
@@ -135,4 +136,19 @@ class IssuesTests {
         }
         Unit
     }
+
+    @Test(timeout = 16000)
+    fun issue75_workaround() = with(Helper(75)) {
+        transcode {
+            val vds = input("bbb_720p_30mb.mp4")
+            addDataSource(ClipDataSource(vds, 0, 500_000))
+            setVideoTrackStrategy(DefaultVideoStrategy.exact(300, 300).build())
+            // API 23:
+            // This video seems to have wrong number of channels in metadata (6) wrt MediaCodec decoder output (2)
+            // so when using DefaultAudioStrategy.CHANNELS_AS_INPUT we target 6 and try to upscale from 2 to 6, which fails
+            // The workaround below explicitly sets a number of channels different than CHANNELS_AS_INPUT to make it work
+            // setAudioTrackStrategy(DefaultAudioStrategy.builder().channels(1).build())
+        }
+        Unit
+    }
 }

lib/src/androidTest/assets/issue_75/bbb_720p_30mb.mp4

@@ -23,11 +23,11 @@ internal interface AudioRemixer {
 
     companion object {
         internal operator fun get(inputChannels: Int, outputChannels: Int): AudioRemixer = when {
+            inputChannels == outputChannels -> PassThroughAudioRemixer()
             inputChannels !in setOf(1, 2) -> error("Input channel count not supported: $inputChannels")
-            outputChannels !in setOf(1, 2) -> error("Output channel count not supported: $inputChannels")
+            outputChannels !in setOf(1, 2) -> error("Output channel count not supported: $outputChannels")
             inputChannels < outputChannels -> UpMixAudioRemixer()
-            inputChannels > outputChannels -> DownMixAudioRemixer()
-            else -> PassThroughAudioRemixer()
+            else -> DownMixAudioRemixer()
         }
     }
 }