Reduce memory consumption of decoder extension input/output buffers

I find that `LibvpxVideoRenderer` has hold 16 inputbuffer and 16 outputbuffer. All these buffer are allocated in java layout. For example , a 720p video:
**InputBuffer:** 16\*INITIAL_INPUT_BUFFER_SIZE = 16\*768 \* 1024=12M
**Outputbuffer:**: 16\*1280\*720\*3/2 = 21M
Allocate 33M memory in java layout is very easy to oom. I suggest that:
1. reduce the buffer size to 4
2. allocate and free the buffer in native(C) layout