h264 h265 nal type計算方式 關鍵幀判斷

來自老陳的 media-server
h265

 nal_type = (nalu[0] >> 1) & 0x3f;

判斷一個h265 nal單元是否是I幀

// Rec. ITU-T H.265 v4 (12/2016) (p26)
// intra random access point (IRAP) picture: 
//   A coded picture for which each VCL NAL unit has nal_unit_type 
//   in the range of BLA_W_LP to RSV_IRAP_VCL23, inclusive.
static int mpeg_h265_find_keyframe(const uint8_t* p, size_t bytes)
{
	size_t i;
	uint8_t type;
	for (i = 2; i + 1 < bytes; i++)
	{
		if (0x01 == p[i] && 0x00 == p[i - 1] && 0x00 == p[i - 2])
		{
			type = (p[i + 1] >> 1) & 0x3f;
			if (type < 32)
				return (16 <= type && type <= 23) ? 1 : 0;
		}
	}

	return 0;
}