src/main/java/org/jcodec/codecs/h264/H264Encoder.java
public ByteBuffer encodePFrame(Picture pic, ByteBuffer _out) {
        frameNumber++;
        return doEncodeFrame(pic, _out, true, frameNumber, SliceType.P);
    }
public ByteBuffer encodePFrame(Picture pic, ByteBuffer _out) {
        frameNumber++;
        return doEncodeFrame(pic, _out, true, frameNumber, SliceType.P);
    }
Encode this picture as a P-frame. P-frame is an frame predicted from one
or more of the previosly decoded frame and is usually 10x less in size
then the IDR frame.

@param pic
@param _out
@return