Pick the first format in the list of supported as something closest
to 640x480 instead of the lowest possible resolution.
Applications that don't suggest a default size will then get something
more sensible than a poster frame.
Keep track of the negotiated parameters and use those to construct
the Buffers param.
Use the FrameAllocator to allocate buffer memory. Keep a request for
each buffer and queue them.
In requestComplete, put the request metadata info into the buffer and
header and write the finished buffer id to a ringbuffer. Then wake up
the data thread to pop the finished buffer_id and push it in the
graph.
Remove some old files.
