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+---------------+      |0|1|2|3|4|5|6|7|      +-+-+-+-+-+-+-+-+      |F|NRI|  Type   |      +---------------+F      :   forbidden zero bit, 一定為0NRI :  nal_ref_idc, 表示資料的重要性, 00為最不重要.Type :nal_unit_type, H.264只定義1~23的範圍一個H.264 raw data看起來像這樣00 00 00 01 09 30 ......2.RTP header因為一個H.264 video frame資料的大小往往會在數k bytes到數十K bytes,在傳送封包時就會將資料切割分別封裝,也因此需要加入一些額外的參數讓接收端可以正確組合被分割的video frame.這也是RFC3984最主要的目的.RTP header 中有三個參數要注意timestamp : 以90KHz作為基準,以30 fps為例,timestamp遞增 90000 / 30.            實務上是以payload實際間隔時間作計算.同一個video frame的            分割資料timestamp是相同的sequence : 每個RTP封包sequence number都遞增.mark bit : RTP封包封裝的是最後一個分割的video frame時mark bit 為 1.2.Payload format1~23 : Single NAL unit packet.RFC3984使用了H.264 NALU中未定義的type 24~29 (相當於增加H.264 nal_unit_type定義)24 : STAP-A 單一時間組合25 : STAP-B 單一時間組合26 : MTAP16 多個時間組合27 : MTAP32 多個時間組合28 : FU-A 分割資料29 : FU-B 分割資料比較常見的是28,29.3.Single NAL unit packet當資料少於MTU的大小就用此方式封裝.H.264 raw data foramt 為 [Start code][NALU][Raw Data]封裝時去掉Start Code即可.Format 如下[RTP Header][NALU][Raw Date]4.FU-A (Fragmentation unit)當資料大於MTU以此方式分割H.264 raw data foramt 為 [Start code][NALU][Raw Data]去掉[Start code],[NALU],以不超過MTU大小分割[Raw Data]以NALU產生FU indicator, FU Header.RFC 3984       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | FU indicator  |   FU header   |                               |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |      |                                                               |      |                         FU payload                            |      |                                                               |      |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                               :...OPTIONAL RTP padding        |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      Figure 14.  RTP payload format for FU-A   The FU indicator octet has the following format:      +---------------+      |0|1|2|3|4|5|6|7|      +-+-+-+-+-+-+-+-+      |F|NRI|  Type   |      +---------------+   The FU header has the following format:      +---------------+      |0|1|2|3|4|5|6|7|      +-+-+-+-+-+-+-+-+      |S|E|R|  Type   |      +---------------+[FU indicator] = (NALU & 0x60) | 28;[FU Header] = (start << 7) | (end << 6) | (NALU & 0x1f);format如下[RTP Header][FU indicator][FU header][Raw Data Part 0][RTP Header][FU indicator][FU header][Raw Data Part 1][RTP Header][FU indicator][FU header][Raw Data Part 2]...5.FU-B (Fragmentation unit)RFC 3984       0                   1                   2                   3       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      | FU indicator  |   FU header   |               DON             |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|      |                                                               |      |                         FU payload                            |      |                                                               |      |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      |                               :...OPTIONAL RTP padding        |      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      Figure 15.  RTP payload format for FU-Bformat如下[RTP Header][FU indicator][FU header][DON][Raw Data Part 0][RTP Header][FU indicator][FU header][DON][Raw Data Part 1][RTP Header][FU indicator][FU header][DON][Raw Data Part 2]...6.Encoding sample code with TI DSP        /* Write the encoded frame to the network */        if (Buffer_getNumBytesUsed(hOutBuf)) {            struct iovec data[3];            rtp_hdr_t rtp;            rtp.version = 2;            rtp.p = 0;            rtp.x = 0;            rtp.cc = 0;            rtp.m = 0;            rtp.pt = 96;                      rtp.seq = htons( sequence );            rtp.ts = htonl( timestamp );                      rtp.ssrc = 10;            data[0].iov_base = &rtp;            data[0].iov_len = sizeof(rtp_hdr_t);            unsigned char *ptr = (unsigned char *)Buffer_getUserPtr(hOutBuf);            size_t len = Buffer_getNumBytesUsed(hOutBuf);            size_t mtu = DEFAULT_MTU;            /* Skip NAL Start Code 00 00 00 01 */            unsigned char nalType = ptr[4] & 0x1f;            //printf("Processing Buffer with NAL TYPE=%d\n", nalType);            if(len < (mtu - sizeof(rtp_hdr_t))) {              /* Remove NAL Start Code 00 00 00 01 */              data[1].iov_base = (void *)ptr + 4;              data[1].iov_len = len - 4;              //printf("NAL Unit fit in one packet size=%d\n", len);              /* only set the marker bit on packets containing access units */              if (IS_ACCESS_UNIT (nalType))                rtp.m = 1;              writev(sfd, data, 2);                    sequence++;            } else  {              int start = 1, end = 0;              /* We keep 2 bytes for FU indicator and FU Header */              unsigned payload_len = mtu - sizeof(rtp_hdr_t) - 2;               unsigned char nalHeader = ptr[4];              /* Remove NAL Start Code 00 00 00 01 and NAL Type*/              ptr += 5;              len -= 5;              //printf("Using FU-A fragmentation for data size=%d\n", len);              while(end == 0)  {                unsigned char fu[2];                payload_len = len < payload_len ? len : payload_len;                if (payload_len == len)                  end = 1;                if (IS_ACCESS_UNIT (nalType))                  rtp.m = end;                /* FU indicator */                fu[0] = (nalHeader & 0x60) | 28;                /* FU Header */                fu[1] = (start << 7) | (end << 6) | (nalHeader & 0x1f);                rtp.seq = htons( sequence );                data[1].iov_base = fu;                data[1].iov_len = 2;                data[2].iov_base = (void *)ptr;                data[2].iov_len = payload_len;                        writev(sfd, data, 3);                start = 0;                ptr += payload_len;                len -= payload_len;                sequence++;              }            }            if (Time_delta(hTimestamp, &time) < 0) {                printf("Failed to get timer delta\n");                goto cleanup;            }              //printf("Read time: %uus\n", (Uns)time);            timestamp += (unsigned int)(0.09 * time);  /*15 fps : 90000 / 15*/        }

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