Working with metadata in Matroska (MKV) files

Reading matroska format-specific properties

The GroupDocs.Metadata API supports extracting format-specific information from MKV files.

The following are the steps to read native MKV metadata.

  1. Load an MKV video
  2. Get the root metadata package
  3. Extract  the native metadata package using the MatroskaRootPackage.getMatroskaPackage method
  4. Read the Matroska metadata properties on different levels of the format structure

advanced_usage.managing_metadata_for_specific_formats.video.matroska.MatroskaReadNativeMetadataProperties

try (Metadata metadata = new Metadata(Constants.InputMkv)) {
	MatroskaRootPackage root = metadata.getRootPackageGeneric();
	// Read the EBML header
	System.out.println(String.format("DocType: %s", root.getMatroskaPackage().getEbmlHeader().getDocType()));
	System.out.println(String.format("DocTypeReadVersion: %s", root.getMatroskaPackage().getEbmlHeader().getDocTypeReadVersion()));
	System.out.println(String.format("DocTypeVersion: %s", root.getMatroskaPackage().getEbmlHeader().getDocTypeVersion()));
	System.out.println(String.format("ReadVersion: %s", root.getMatroskaPackage().getEbmlHeader().getReadVersion()));
	System.out.println(String.format("Version: %s", root.getMatroskaPackage().getEbmlHeader().getVersion()));

	// Read Matroska segment information
	for (MatroskaSegment segment : root.getMatroskaPackage().getSegments()) {
		System.out.println(String.format("DateUtc: %s", segment.getDateUtc()));
		System.out.println(String.format("Duration: %s", segment.getDuration()));
		System.out.println(String.format("MuxingApp: %s", segment.getMuxingApp()));
		System.out.println(String.format("SegmentFilename: %s", segment.getSegmentFilename()));
		System.out.println(String.format("SegmentUid: %s", segment.getSegmentUid()));
		System.out.println(String.format("TimecodeScale: %s", segment.getTimecodeScale()));
		System.out.println(String.format("Title: %s", segment.getTitle()));
		System.out.println(String.format("WritingApp: %s", segment.getWritingApp()));
	}

	// Read Matroska tag metadata
	for (MatroskaTag tag : root.getMatroskaPackage().getTags()) {
		System.out.println(String.format("TargetType: %s", tag.getTargetType()));
		System.out.println(String.format("TargetTypeValue: %s", tag.getTargetTypeValue()));
		System.out.println(String.format("TagTrackUid: %s", tag.getTagTrackUid()));
		for (MetadataProperty simpleTag : tag.getSimpleTags()) {
			System.out.println(String.format("Name: %s", simpleTag.getName()));
			System.out.println(String.format("Value: %s", simpleTag.getValue()));
		}
	}

	// Read Matroska track metadata
	for (MatroskaTrack track : root.getMatroskaPackage().getTracks()) {
		System.out.println(String.format("CodecId: %s", track.getCodecID()));
		System.out.println(String.format("CodecName: %s", track.getCodecName()));
		System.out.println(String.format("DefaultDuration: %s", track.getDefaultDuration()));
		System.out.println(String.format("FlagEnabled: %s", track.getFlagEnabled()));
		System.out.println(String.format("Language: %s", track.getLanguage()));
		System.out.println(String.format("LanguageIetf: %s", track.getLanguageIetf()));
		System.out.println(String.format("Name: %s", track.getName()));
		System.out.println(String.format("TrackNumber: %s", track.getTrackNumber()));
		System.out.println(String.format("TrackType: %s", track.getTrackType()));
		System.out.println(String.format("TrackUid: %s", track.getTrackUid()));
		if (track instanceof MatroskaAudioTrack) {
			MatroskaAudioTrack audioTrack = (MatroskaAudioTrack) track;
			System.out.println(String.format("SamplingFrequency: %s", audioTrack.getSamplingFrequency()));
			System.out.println(String.format("OutputSamplingFrequency: %s", audioTrack.getOutputSamplingFrequency()));
			System.out.println(String.format("Channels: %s", audioTrack.getChannels()));
			System.out.println(String.format("BitDepth: %s", audioTrack.getBitDepth()));
		}
		if (track instanceof MatroskaVideoTrack) {
			MatroskaVideoTrack videoTrack = (MatroskaVideoTrack) track;
			System.out.println(String.format("FlagInterlaced: %s", videoTrack.getFlagInterlaced()));
			System.out.println(String.format("FieldOrder: %s", videoTrack.getFieldOrder()));
			System.out.println(String.format("StereoMode: %s", videoTrack.getStereoMode()));
			System.out.println(String.format("AlphaMode: %s", videoTrack.getAlphaMode()));
			System.out.println(String.format("PixelWidth: %s", videoTrack.getPixelWidth()));
			System.out.println(String.format("PixelHeight: %s", videoTrack.getPixelHeight()));
			System.out.println(String.format("PixelCropBottom: %s", videoTrack.getPixelCropBottom()));
			System.out.println(String.format("PixelCropTop: %s", videoTrack.getPixelCropTop()));
			System.out.println(String.format("PixelCropLeft: %s", videoTrack.getPixelCropLeft()));
			System.out.println(String.format("PixelCropRight: %s", videoTrack.getPixelCropRight()));
			System.out.println(String.format("DisplayWidth: %s", videoTrack.getDisplayWidth()));
			System.out.println(String.format("DisplayHeight: %s", videoTrack.getDisplayHeight()));
			System.out.println(String.format("DisplayUnit: %s", videoTrack.getDisplayUnit()));
		}
	}
}

Extracting subtitles from a Matroska video

The GroupDocs.Metadata API also provides a convenient way of extracting subtitles attached to a Matroska video. The code sample below demonstrates how to extract multilingual subtitles from an MKV file.

  1. Load an MKV video
  2. Get the root metadata package
  3. Use the MatroskaPackage.getSubtitleTracks method to extract sets of subtitles in different languages

advanced_usage.managing_metadata_for_specific_formats.video.matroska.MatroskaReadSubtitles

try (Metadata metadata = new Metadata(Constants.MkvWithSubtitles)) {
	MatroskaRootPackage root = metadata.getRootPackageGeneric();

	for (MatroskaSubtitleTrack subtitleTrack : root.getMatroskaPackage().getSubtitleTracks()) {
		System.out.println(subtitleTrack.getLanguageIetf() != null ? subtitleTrack.getLanguageIetf() : subtitleTrack.getLanguage());
		for (MatroskaSubtitle subtitle : subtitleTrack.getSubtitles()) {
			System.out.println(String.format("Timecode=%s, Duration=%s", subtitle.getTimecode(), subtitle.getDuration()));
			System.out.println(subtitle.getText());
		}
	}
}

More resources

GitHub examples

You may easily run the code above and see the feature in action in our GitHub examples:

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