Using mp4parser , how can I handle videos that are taken from Uri and ContentResolver?

Question

Background

We want to let the user choose a video from any app, and then trim a video to be of max of 5 seconds.

The problem

For getting a Uri to

Answer 1

Next a snipped shows how to open a MediaStore Uri with IsoFile from Mp4Parser. So, you can see how to get a FileChannel from a Uri.

public void test(@NonNull final Context context, @NonNull final Uri uri) throws IOException
{
    ParcelFileDescriptor fileDescriptor = null;

    try
    {
        final ContentResolver resolver = context.getContentResolver();
        fileDescriptor = resolver.openFileDescriptor(uri, "rw");

        if (fileDescriptor == null)
        {
            throw new IOException("Failed to open Uri.");
        }

        final FileDescriptor  fd          = fileDescriptor.getFileDescriptor();
        final FileInputStream inputStream = new FileInputStream(fd);
        final FileChannel     fileChannel = inputStream.getChannel();

        final DataSource channel = new FileDataSourceImpl(fileChannel);
        final IsoFile    isoFile = new IsoFile(channel);

        ... do what you need ....
    }
    finally
    {
        if (fileDescriptor != null)
        {
            fileDescriptor.close();
        }
    }
}

Answer 2

First of all a caveat: I am not familiar with the mp4parser library but your question looked interesting so I took a look.

I think its worth you looking at one of the classes the code comments say is "mainly for testing". InMemRandomAccessSourceImpl. To create a Movie from any URI, the code would be as follows:

try {
    InputStream  inputStream = getContentResolver().openInputStream(uri);
    Log.e("InputStream Size","Size " + inputStream);
    int  bytesAvailable = inputStream.available();
    int bufferSize = Math.min(bytesAvailable, MAX_BUFFER_SIZE);
    final byte[] buffer = new byte[bufferSize];

    int read = 0;
    int total = 0;
    while ((read = inputStream.read(buffer)) !=-1 ) {
        total += read;
    }
    if( total < bytesAvailable ){
        Log.e(TAG, "Read from input stream failed")
        return;
    }
    //or try inputStream.readAllBytes() if using Java 9
    inputStream.close();

    ByteBuffer bb = ByteBuffer.wrap(buffer);
    Movie m2 = MovieCreator.build(new ByteBufferByteChannel(bb),
        new InMemRandomAccessSourceImpl(bb), "inmem");

} catch (FileNotFoundException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}

But I would say, there looks to be somewhat of a conflict between what you want to achieve and the approach the parser takes. It is depending on local files to avoid large memory overheads, and random access to bytes can only be done if the entire set of data is available, which differs from a streaming approach.

It will require buffering at least the amount of data required for your clip in one go before the parser is given the buffer. That might be workable for you if you are looking to grab short sections and the buffering is not too cumbersome. You may be subject to IO exceptions and the like if the read from the InputStream has issues, especially if it is remote content, whereas you really aren't expecting that with a file on a modern system.

There is also MemoryFile to consider which provides an ashmem backed file-like object. I think somehow that could be worked in.