Don't fail if we find a track is unsupported

Use AUDIO_UNKNOWN instead. This is in line with our handling
of video tracks with VIDEO_UNKNOWN.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=157209428

library/core/src/main/java/com/google/android/exoplayer2/extractor/mkv/MatroskaExtractor.java

@@ -16,6 +16,7 @@
 package com.google.android.exoplayer2.extractor.mkv;
 
 import android.support.annotation.IntDef;
+import android.util.Log;
 import android.util.SparseArray;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.Format;
@@ -84,6 +85,8 @@ public final class MatroskaExtractor implements Extractor {
    */
   public static final int FLAG_DISABLE_SEEK_FOR_CUES = 1;
 
+  private static final String TAG = "MatroskaExtractor";
+
   private static final int UNSET_ENTRY_ID = -1;
 
   private static final int BLOCK_STATE_START = 0;
@@ -1559,7 +1562,12 @@ public final class MatroskaExtractor implements Extractor {
           break;
         case CODEC_ID_FOURCC:
           initializationData = parseFourCcVc1Private(new ParsableByteArray(codecPrivate));
-          mimeType = initializationData == null ? MimeTypes.VIDEO_UNKNOWN : MimeTypes.VIDEO_VC1;
+          if (initializationData != null) {
+            mimeType = MimeTypes.VIDEO_VC1;
+          } else {
+            Log.w(TAG, "Unsupported FourCC. Setting mimeType to " + MimeTypes.VIDEO_UNKNOWN);
+            mimeType = MimeTypes.VIDEO_UNKNOWN;
+          }
           break;
         case CODEC_ID_THEORA:
           // TODO: This can be set to the real mimeType if/when we work out what initializationData
@@ -1615,19 +1623,27 @@ public final class MatroskaExtractor implements Extractor {
           break;
         case CODEC_ID_ACM:
           mimeType = MimeTypes.AUDIO_RAW;
-          if (!parseMsAcmCodecPrivate(new ParsableByteArray(codecPrivate))) {
-            throw new ParserException("Non-PCM MS/ACM is unsupported");
-          }
-          pcmEncoding = Util.getPcmEncoding(audioBitDepth);
-          if (pcmEncoding == C.ENCODING_INVALID) {
-            throw new ParserException("Unsupported PCM bit depth: " + audioBitDepth);
+          if (parseMsAcmCodecPrivate(new ParsableByteArray(codecPrivate))) {
+            pcmEncoding = Util.getPcmEncoding(audioBitDepth);
+            if (pcmEncoding == C.ENCODING_INVALID) {
+              pcmEncoding = Format.NO_VALUE;
+              mimeType = MimeTypes.AUDIO_UNKNOWN;
+              Log.w(TAG, "Unsupported PCM bit depth: " + audioBitDepth + ". Setting mimeType to "
+                  + mimeType);
+            }
+          } else {
+            mimeType = MimeTypes.AUDIO_UNKNOWN;
+            Log.w(TAG, "Non-PCM MS/ACM is unsupported. Setting mimeType to " + mimeType);
           }
           break;
         case CODEC_ID_PCM_INT_LIT:
           mimeType = MimeTypes.AUDIO_RAW;
           pcmEncoding = Util.getPcmEncoding(audioBitDepth);
           if (pcmEncoding == C.ENCODING_INVALID) {
-            throw new ParserException("Unsupported PCM bit depth: " + audioBitDepth);
+            pcmEncoding = Format.NO_VALUE;
+            mimeType = MimeTypes.AUDIO_UNKNOWN;
+            Log.w(TAG, "Unsupported PCM bit depth: " + audioBitDepth + ". Setting mimeType to "
+                + mimeType);
           }
           break;
         case CODEC_ID_SUBRIP:

library/core/src/main/java/com/google/android/exoplayer2/util/MimeTypes.java

@@ -61,6 +61,7 @@ public final class MimeTypes {
   public static final String AUDIO_AMR_WB = BASE_TYPE_AUDIO + "/amr-wb";
   public static final String AUDIO_FLAC = BASE_TYPE_AUDIO + "/x-flac";
   public static final String AUDIO_ALAC = BASE_TYPE_AUDIO + "/alac";
+  public static final String AUDIO_UNKNOWN = BASE_TYPE_AUDIO + "/x-unknown";
 
   public static final String TEXT_VTT = BASE_TYPE_TEXT + "/vtt";