H.264 将构成一帧图像所有NALU(network abstract layer unit)的集合称为一个AU(access unit) ，一个NALU 是一个最小网络传输单元，一个AU是一帧数据
I think Technically speaking the only way to detect when a frame ends is to see where the next one begins、That means, you should search for the next start prefix code 0x000001.
00 00 00 01 61 (P帧)
00 00 00 01 65 ( IDR 帧)
00 00 00 01 67 (SPS) sequence parameter set
00 00 00 01 68 (PPS)