Enable embedded CEA-708 support

[jruesga]

Currently, DashMediaPeriod only takes into account as CEA-608 accessibility tags as embedded closed captions tracks CEA-608. CEA-708 closed captions format is parsed when is present on its own AdaptationSet, but not when is embedded as an accessibility tag in a video AdaptationSet.

Embedded CEA-708 support is added by parsing accessibility tags like the example below:

<Accessibility schemeIdUri="urn:scte:dash:cc:cea-708:2015" value="1=lang:eng;2=lang:deu"/>
<Accessibility schemeIdUri="urn:scte:dash:cc:cea-708:2015" value="1=lang:eng;2=lang:eng,war:1,er:1"/>

Creates a new CEA-708 track for accessibility tags with schemeIdUri urn:scte:dash:cc:cea-708:2015 and extract accessibilityChannel and language from value attribute.

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[jruesga]

@googlebot I signed it!

[ojw28]

I'm not sure why the CLA check is unhappy. Marking with the cla: yes label based on manual verification.

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[ojw28]

Please take a look at the comments. Thanks!

[ojw28]

The use of the enum through this code is IMO making it quite a bit harder to read than it needs to be. Can't you just do something like (warning, untested):

  private static Format[] getClosedCaptionTrackFormats(
      List<AdaptationSet> adaptationSets, int[] adaptationSetIndices) {
    for (int i : adaptationSetIndices) {
      AdaptationSet adaptationSet = adaptationSets.get(i);
      List<Descriptor> descriptors = adaptationSets.get(i).accessibilityDescriptors;
      for (int j = 0; j < descriptors.size(); j++) {
        Descriptor descriptor = descriptors.get(j);
        if ("urn:scte:dash:cc:cea-608:2015".equals(descriptor.schemeIdUri)) {
          Format cea608Format =
              new Format.Builder()
                  .setSampleMimeType(MimeTypes.APPLICATION_CEA608)
                  .setId(adaptationSet.id + ":cea608")
                  .build();
          return parseClosedCaptionDescriptor(
              descriptor, CEA608_SERVICE_DESCRIPTOR_REGEX, cea608Format);
        } else if ("urn:scte:dash:cc:cea-708:2015".equals(descriptor.schemeIdUri)) {
          Format cea708Format =
              new Format.Builder()
                  .setSampleMimeType(MimeTypes.APPLICATION_CEA708)
                  .setId(adaptationSet.id + ":cea708")
                  .build();
          return parseClosedCaptionDescriptor(
              descriptor, CEA708_SERVICE_DESCRIPTOR_REGEX, cea708Format);
        }
      }
    }
    return new Format[0];
  }

  private static Format[] parseClosedCaptionDescriptor(
      Descriptor descriptor, Pattern serviceDescriptorRegex, Format baseFormat) {
    @Nullable String value = descriptor.value;
    if (value == null) {
      // There are embedded closed caption tracks, but service information is not declared.
      return new Format[] {baseFormat};
    }
    String[] services = Util.split(value, ";");
    Format[] formats = new Format[services.length];
    for (int i = 0; i < services.length; i++) {
      Matcher matcher = serviceDescriptorRegex.matcher(services[i]);
      if (!matcher.matches()) {
        // If we can't parse service information for all services, assume a single track.
        return new Format[] {baseFormat};
      }
      int accessibilityChannel = Integer.parseInt(matcher.group(1));
      formats[i] =
          baseFormat
              .buildUpon()
              .setId(baseFormat.id + ":" + accessibilityChannel)
              .setAccessibilityChannel(accessibilityChannel)
              .setLanguage(matcher.group(2))
              .build();
    }
    return formats;
  }

and get rid of the enum and all the little helper methods.

[jruesga]

Done

[ojw28]

Might be irrelevant if you can go with my proposal above, but this shouldn't return if parsedClosedCaptionsDescriptor returned null. Else parsing will fail if there's a descriptor for something other than 608/708 before the descriptor you're looking for.

[jruesga]

Done

[ojw28]

I'm not sure why it's not been picked up, but this was merged in 3db703a. Thanks!