一、NALU概念
NAL的全称是Network abstraction layer,叫网络抽象层，它保存了H264相关的参数信息和图像信息，NAL层由多个单元NALU组成,NALU由了NALU头（00 00 00 01或者00 00 01）、sps(序列参数集)、pps(图像参数集合)、slice、sei、IDR帧、I帧、P帧、B帧等数据。
二、有啥用
在一个完整的视频流 第一个图像帧是IDR帧，IDR帧是强制刷新帧，在解码过程中，当出现了IDR帧时，要更新sps、pps，原因是防止前面I帧错误，导致sps，pps参考I帧导致无法纠正。
三、H264 NAUL
#define NALU_TYPE_SLICE 1
#define NALU_TYPE_DPA 2
#define NALU_TYPE_DPB 3
#define NALU_TYPE_DPC 4
#define NALU_TYPE_IDR 5
#define NALU_TYPE_SEI 6
#define NALU_TYPE_SPS 7
#define NALU_TYPE_PPS 8
#define NALU_TYPE_AUD 9
#define NALU_TYPE_EOSEQ 10
#define NALU_TYPE_EOSTREAM 11
#define NALU_TYPE_FILL 12
其中重要的是 IDR 5
四、H265 NAUL
NAL_TRAIL_N = 0,
NAL_TRAIL_R = 1,
NAL_TSA_N = 2,
NAL_TSA_R = 3,
NAL_STSA_N = 4,
NAL_STSA_R = 5,
NAL_RADL_N = 6,
NAL_RADL_R = 7,
NAL_RASL_N = 8,
NAL_RASL_R = 9,
NAL_BLA_W_LP = 16,
NAL_BLA_W_RADL = 17,
NAL_BLA_N_LP = 18,
NAL_IDR_W_RADL = 19,
NAL_IDR_N_LP = 20,
NAL_CRA_NUT = 21,
NAL_VPS = 32,
NAL_SPS = 33,
NAL_PPS = 34,
NAL_AUD = 35,
NAL_EOS_NUT = 36,
NAL_EOB_NUT = 37,
NAL_FD_NUT = 38,
NAL_SEI_PREFIX = 39,
NAL_SEI_SUFFIX = 40,
其中重要的是 I帧 19
五、获取NaulType
private static int getH264NaluType(byte[] buffer) {
if (buffer.length > 4 && (buffer[0] == 0x0) && (0x0 == buffer[1]) && (buffer[2] == 0x0)
&& (0x01 == buffer[3])) {
return buffer[4] & 0x1F;
} else if (buffer.length > 3 && (buffer[0] == 0x0) && (0x0 == buffer[1]) && (0x01 == buffer[2])) {
return buffer[3] & 0x1F;
} else if (buffer.length > 1) {
return buffer[0] & 0x1F;
} else {
return 0;
}
}
private static int getH265NaluType(byte[] buffer) {
if (buffer.length > 4 && (buffer[0] == 0x0) && (0x0 == buffer[1]) && (buffer[2] == 0x0)
&& (0x01 == buffer[3])) {
return (buffer[4] >> 1) & 0x3F;
} else if (buffer.length > 3 && (buffer[0] == 0x0) && (0x0 == buffer[1]) && (0x01 == buffer[2])) {
return (buffer[3] >> 1) & 0x3F;
} else if (buffer.length > 1) {
return (buffer[0] >> 1) & 0x3F;
} else {
return 0;
}
}