Step 2: Write and examine the code

In this section, you examine the Java library and test code, and learn how to use the tools from the library in your own code.

The Kinesis video stream Parser Library contains the following tools:

• StreamingMkvReader

• FragmentMetadataVisitor

• OutputSegmentMerger

• KinesisVideoExample

StreamingMkvReader

This class reads specified MKV elements from a stream in a non-blocking way.

The following code example (from FragmentMetadataVisitorTest) shows how to create and use a Streaming MkvReader to retrieve MkvElement objects from an input stream called inputStream:

StreamingMkvReader mkvStreamReader =
                StreamingMkvReader.createDefault(new InputStreamParserByteSource(inputStream));
        while (mkvStreamReader.mightHaveNext()) {
            Optional<MkvElement> mkvElement = mkvStreamReader.nextIfAvailable();
            if (mkvElement.isPresent()) {
                mkvElement.get().accept(fragmentVisitor);
                ...
                }
            }
        }

FragmentMetadataVisitor

This class retrieves metadata for fragments (media elements) and tracks individual data streams containing media information, such as codec private data, pixel width, or pixel height.

The following code example (from the FragmentMetadataVisitorTest file) shows how to use FragmentMetadataVisitor to retrieve data from a MkvElement object:

FragmentMetadataVisitor fragmentVisitor = FragmentMetadataVisitor.create();
        StreamingMkvReader mkvStreamReader =
                StreamingMkvReader.createDefault(new InputStreamParserByteSource(in));
        int segmentCount = 0;
        while(mkvStreamReader.mightHaveNext()) {
            Optional<MkvElement> mkvElement = mkvStreamReader.nextIfAvailable();
            if (mkvElement.isPresent()) {
                mkvElement.get().accept(fragmentVisitor);
                if (MkvTypeInfos.SIMPLEBLOCK.equals(mkvElement.get().getElementMetaData().getTypeInfo())) {
                    MkvDataElement dataElement = (MkvDataElement) mkvElement.get();
                    Frame frame = ((MkvValue<Frame>)dataElement.getValueCopy()).getVal();
                    MkvTrackMetadata trackMetadata = fragmentVisitor.getMkvTrackMetadata(frame.getTrackNumber());
                    assertTrackAndFragmentInfo(fragmentVisitor, frame, trackMetadata);
                }
                if (MkvTypeInfos.SEGMENT.equals(mkvElement.get().getElementMetaData().getTypeInfo())) {
                    if (mkvElement.get() instanceof MkvEndMasterElement) {
                        if (segmentCount < continuationTokens.size()) {
                            Optional<String> continuationToken = fragmentVisitor.getContinuationToken();
                            Assert.assertTrue(continuationToken.isPresent());
                            Assert.assertEquals(continuationTokens.get(segmentCount), continuationToken.get());
                        }
                        segmentCount++;
                    }
                }
            }

        }

The preceding example shows the following coding pattern:

• Create a FragmentMetadataVisitor to parse the data, and a StreamingMkvReader to provide the data.

• For each MkvElement in the stream, test if its metadata is of type SIMPLEBLOCK.

• If it is, retrieve the MkvDataElement from the MkvElement.

• Retrieve the Frame (media data) from the MkvDataElement.

• Retrieve the MkvTrackMetadata for the Frame from the FragmentMetadataVisitor.

• Retrieve and verify the following data from the Frame and MkvTrackMetadata objects:

  • The track number.

  • The frame's pixel height.

  • The frame's pixel width.

  • The codec ID for the codec used to encode the frame.

  • That this frame arrived in order. Verify that the track number of the previous frame, if present, is less than that of the current frame.

To use FragmentMetadataVisitor in your project, pass MkvElement objects to the visitor using their accept method:

mkvElement.get().accept(fragmentVisitor);

OutputSegmentMerger

This class merges metadata from different tracks in the stream into a stream with a single segment.

The following code example (from the FragmentMetadataVisitorTest file) shows how to use OutputSegmentMerger to merge track metadata from a byte array called inputBytes:

FragmentMetadataVisitor fragmentVisitor = FragmentMetadataVisitor.create();

ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

OutputSegmentMerger outputSegmentMerger =
    OutputSegmentMerger.createDefault(outputStream);

CompositeMkvElementVisitor compositeVisitor =
    new TestCompositeVisitor(fragmentVisitor, outputSegmentMerger);

final InputStream in = TestResourceUtil.getTestInputStream("output_get_media.mkv");

StreamingMkvReader mkvStreamReader =
    StreamingMkvReader.createDefault(new InputStreamParserByteSource(in));
    
while (mkvStreamReader.mightHaveNext()) {
    Optional<MkvElement> mkvElement = mkvStreamReader.nextIfAvailable();
    if (mkvElement.isPresent()) {
        mkvElement.get().accept(compositeVisitor);
    if (MkvTypeInfos.SIMPLEBLOCK.equals(mkvElement.get().getElementMetaData().getTypeInfo())) {
        MkvDataElement dataElement = (MkvDataElement) mkvElement.get();
        Frame frame = ((MkvValue<Frame>) dataElement.getValueCopy()).getVal();
        Assert.assertTrue(frame.getFrameData().limit() > 0);
        MkvTrackMetadata trackMetadata = fragmentVisitor.getMkvTrackMetadata(frame.getTrackNumber());
        assertTrackAndFragmentInfo(fragmentVisitor, frame, trackMetadata);
    }
}

The preceding example shows the following coding pattern:

• Create a FragmentMetadataVisitorto retrieve the metadata from the stream.

• Create an output stream to receive the merged metadata.

• Create an OutputSegmentMerger, passing in the ByteArrayOutputStream.

• Create a CompositeMkvElementVisitor that contains the two visitors.

• Create an InputStream that points to the specified file.

• Merge each element in the input data into the output stream.

KinesisVideoExample

This is a sample application that shows how to use the Kinesis video stream Parser Library.

This class performs the following operations:

• Creates a Kinesis video stream. If a stream with the given name already exists, the stream is deleted and recreated.

• Calls PutMedia to stream video fragments to the Kinesis video stream.

• Calls GetMedia to stream video fragments out of the Kinesis video stream.

• Uses a StreamingMkvReader to parse the returned fragments on the stream, and uses a FragmentMetadataVisitor to log the fragments.

Delete and recreate the stream

The following code example (from the StreamOps.java file) deletes a given Kinesis video stream:

//Delete the stream
amazonKinesisVideo.deleteStream(new DeleteStreamRequest().withStreamARN(streamInfo.get().getStreamARN()));
            

The following code example (from the StreamOps.java file) creates a Kinesis video stream with the specified name:

amazonKinesisVideo.createStream(new CreateStreamRequest().withStreamName(streamName)
.withDataRetentionInHours(DATA_RETENTION_IN_HOURS)
.withMediaType("video/h264"));

Call PutMedia

The following code example (from the PutMediaWorker.java file) calls PutMedia on the stream:

 putMedia.putMedia(new PutMediaRequest().withStreamName(streamName)
.withFragmentTimecodeType(FragmentTimecodeType.RELATIVE)
.withProducerStartTimestamp(new Date())
.withPayload(inputStream), new PutMediaAckResponseHandler() {
...
});

Call GetMedia

The following code example (from the GetMediaWorker.java file) calls GetMedia on the stream:

GetMediaResult result = videoMedia.getMedia(new GetMediaRequest().withStreamName(streamName).withStartSelector(startSelector));

Parse the GetMedia result

This section describes how to use StreamingMkvReader, FragmentMetadataVisitor and CompositeMkvElementVisitor to parse, save to file, and log the data returned from GetMedia.

Read the output of GetMedia with StreamingMkvReader

The following code example (from the GetMediaWorker.java file) creates a StreamingMkvReader and uses it to parse the result from the GetMedia operation:

StreamingMkvReader mkvStreamReader = StreamingMkvReader.createDefault(new InputStreamParserByteSource(result.getPayload()));
log.info("StreamingMkvReader created for stream {} ", streamName);
try {
    mkvStreamReader.apply(this.elementVisitor);
} catch (MkvElementVisitException e) {
    log.error("Exception while accepting visitor {}", e);
}

In the preceding code example, the StreamingMkvReader retrieves MKVElement objects from the payload of the GetMedia result. In the next section, the elements are passed to a FragmentMetadataVisitor.

Retrieve fragments with FragmentMetadataVisitor

The following code examples (from the KinesisVideoExample.java and StreamingMkvReader.java files) create a FragmentMetadataVisitor. The MkvElement objects iterated by the StreamingMkvReader are then passed to the visitor using the accept method.

from KinesisVideoExample.java:

FragmentMetadataVisitor fragmentMetadataVisitor = FragmentMetadataVisitor.create();
                        

from StreamingMkvReader.java:

if (mkvElementOptional.isPresent()) {
    //Apply the MkvElement to the visitor
    mkvElementOptional.get().accept(elementVisitor);
        }

Log the elements and write them to a file

The following code example (from the KinesisVideoExample.java file) creates the following objects and returns them as part of the return value of the GetMediaProcessingArguments function:

• A LogVisitor (an extension of MkvElementVisitor) that writes to the system log.

• An OutputStream that writes the incoming data to an MKV file.

• A BufferedOutputStream that buffers data bound for the OutputStream.

• An OutputSegmentMerger that merges consecutive elements in the GetMedia result with the same track and EBML data.

• A CompositeMkvElementVisitor that composes the FragmentMetadataVisitor, OutputSegmentMerger, and LogVisitor into a single element visitor.

//A visitor used to log as the GetMedia stream is processed.
    LogVisitor logVisitor = new LogVisitor(fragmentMetadataVisitor);

    //An OutputSegmentMerger to combine multiple segments that share track and ebml metadata into one
    //mkv segment.
    OutputStream fileOutputStream = Files.newOutputStream(Paths.get("kinesis_video_example_merged_output2.mkv"),
            StandardOpenOption.WRITE, StandardOpenOption.CREATE);
    BufferedOutputStream outputStream = new BufferedOutputStream(fileOutputStream);
    OutputSegmentMerger outputSegmentMerger = OutputSegmentMerger.createDefault(outputStream);

    //A composite visitor to encapsulate the three visitors.
    CompositeMkvElementVisitor mkvElementVisitor =
            new CompositeMkvElementVisitor(fragmentMetadataVisitor, outputSegmentMerger, logVisitor);

    return new GetMediaProcessingArguments(outputStream, logVisitor, mkvElementVisitor);

The media processing arguments are then passed into the GetMediaWorker, which is in turn passed to the ExecutorService, which carries out the worker on a separate thread:

GetMediaWorker getMediaWorker = GetMediaWorker.create(getRegion(),
        getCredentialsProvider(),
        getStreamName(),
        new StartSelector().withStartSelectorType(StartSelectorType.EARLIEST),
        amazonKinesisVideo,
        getMediaProcessingArgumentsLocal.getMkvElementVisitor());
executorService.submit(getMediaWorker);

Next step

Step 3: Run and verify the code