EDIT

Media files can contain metadata (Exif, IPCT, PhotoshopMetadata, etc). The Cdm needs to be able to store data extracted from a media file to avoid fetching and analyzingthe file each time it's metadata is requested.

The data structure will be a cache for

ImageInfo info = new ImageInfo(URI imageUri);
info.getMetaData();
info.getWidth();
info.getHeight();
// etc ...

Since the ImageInfo is fetched for each media URI individually the metadata cache should also extend the MediaRepresentationPart.

Structure of the metadata could be a flat key/value pair list like a Map<String,String>.

Now that ImageInfo and MediaInfo are returning also typed information like width, height, etc it could beneficial to use typed keys and predefined keys with specific types for e.g. with, length, etc ...:

public class MetaDataMap extends HashMap<MetaDataType<T>, T>{

    public static class MetaDataType<T extends Object> {

        public static final MetaDataType<String> stringType = new MetaDataType<String>(String.class);
        public static final MetaDataType<Integer> integerType = new MetaDataType<Integer>(Integer.class);
        public static final MetaDataType<Double> doubleType = new MetaDataType<Double>(Double.class);

        Class<T> type;
        T value;

        private MetaDataType(Class<T> type) {
            this.type = type;
        }

        public void setValue(T value) {
            this.value = value;
        }

        public T getValue() {
            return value;
        }

        public Class<T> getType(){
            return type;
        }

        public boolean hasType(Class otherType) {
            return type.equals(otherType);
        }

    }

    enum MetaDataKey {

        WIDTH(MetaDataMap.MetaDataType.stringType),
        HEIGHT(MetaDataMap.MetaDataType.integerType),
        DURATION(MetaDataMap.MetaDataType.doubleType);

        MetaDataType<?> type;

        private MetaDataKey(MetaDataMap.MetaDataType<?> type){
            this.type = type;
        }
    }
}