Fix handling of text codecs strings in DashManifestParser

Also fix an NPE in FfmpegAudioRenderer if sampleMimeType wasn't set.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=208230947

extensions/ffmpeg/src/main/java/com/google/android/exoplayer2/ext/ffmpeg/FfmpegAudioRenderer.java

@@ -95,7 +95,7 @@ public final class FfmpegAudioRenderer extends SimpleDecoderAudioRenderer {
   protected int supportsFormatInternal(DrmSessionManager<ExoMediaCrypto> drmSessionManager,
       Format format) {
     Assertions.checkNotNull(format.sampleMimeType);
-    if (!FfmpegLibrary.isAvailable() || !MimeTypes.isAudio(format.sampleMimeType)) {
+    if (!FfmpegLibrary.isAvailable()) {
       return FORMAT_UNSUPPORTED_TYPE;
     } else if (!FfmpegLibrary.supportsFormat(format.sampleMimeType, format.pcmEncoding)
         || !isOutputSupported(format)) {

library/core/src/main/java/com/google/android/exoplayer2/audio/SimpleDecoderAudioRenderer.java

@@ -218,6 +218,9 @@ public abstract class SimpleDecoderAudioRenderer extends BaseRenderer implements
 
   @Override
   public final int supportsFormat(Format format) {
+    if (!MimeTypes.isAudio(format.sampleMimeType)) {
+      return FORMAT_UNSUPPORTED_TYPE;
+    }
     int formatSupport = supportsFormatInternal(drmSessionManager, format);
     if (formatSupport <= FORMAT_UNSUPPORTED_DRM) {
       return formatSupport;
@@ -227,15 +230,15 @@ public abstract class SimpleDecoderAudioRenderer extends BaseRenderer implements
   }
 
   /**
-   * Returns the {@link #FORMAT_SUPPORT_MASK} component of the return value for
-   * {@link #supportsFormat(Format)}.
+   * Returns the {@link #FORMAT_SUPPORT_MASK} component of the return value for {@link
+   * #supportsFormat(Format)}.
    *
    * @param drmSessionManager The renderer's {@link DrmSessionManager}.
-   * @param format The format.
+   * @param format The format, which has an audio {@link Format#sampleMimeType}.
    * @return The extent to which the renderer supports the format itself.
    */
-  protected abstract int supportsFormatInternal(DrmSessionManager<ExoMediaCrypto> drmSessionManager,
-      Format format);
+  protected abstract int supportsFormatInternal(
+      DrmSessionManager<ExoMediaCrypto> drmSessionManager, Format format);
 
   /**
    * Returns whether the audio sink can accept audio in the specified encoding.

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/manifest/DashManifestParser.java

@@ -1022,10 +1022,12 @@ public class DashManifestParser extends DefaultHandler
     } else if (mimeTypeIsRawText(containerMimeType)) {
       return containerMimeType;
     } else if (MimeTypes.APPLICATION_MP4.equals(containerMimeType)) {
-      if ("stpp".equals(codecs)) {
-        return MimeTypes.APPLICATION_TTML;
-      } else if ("wvtt".equals(codecs)) {
-        return MimeTypes.APPLICATION_MP4VTT;
+      if (codecs != null) {
+        if (codecs.startsWith("stpp")) {
+          return MimeTypes.APPLICATION_TTML;
+        } else if (codecs.startsWith("wvtt")) {
+          return MimeTypes.APPLICATION_MP4VTT;
+        }
       }
     } else if (MimeTypes.APPLICATION_RAWCC.equals(containerMimeType)) {
       if (codecs != null) {