H265 Rtp封包可以参考Ffmpeg，具体实现在文件rtpenc_h264_hevc.c(4.0.1版本)，核心的方法是nal_send

这个方法有些绕，下面帖子具体的代码及注释。

static void nal_send(AVFormatContext *s1, const uint8_t *buf, int size, int last){    RTPMuxContext *s = s1->priv_data;    enum AVCodecID codec = s1->streams[0]->codecpar->codec_id;    av_log(s1, AV_LOG_DEBUG, "Sending NAL %x of len %d M=%d\n", buf[0] & 0x1F, size, last);    if (size <= s->max_payload_size) {            //max_payload_size一般<= 1500        int buffered_size = s->buf_ptr - s->buf;        int header_size;        int skip_aggregate = 0;        if (codec == AV_CODEC_ID_H264) {            header_size = 1;            skip_aggregate = s->flags & FF_RTP_FLAG_H264_MODE0;        } else {            header_size = 2; //Hevc 头两个字节，第二个字节是0x01;第一个字节表示NAL Type，具体哪些类型可以参考Hevc.h        }        // Flush buffered NAL units if the current unit doesn't fit        if (buffered_size + 2 + size > s->max_payload_size) {            flush_buffered(s1, 0);            buffered_size = 0;        }        // If we aren't using mode 0, and the NAL unit fits including the        // framing (2 bytes length, plus 1/2 bytes for the STAP-A/AP marker),        // write the unit to the buffer as a STAP-A/AP packet, otherwise flush        // and send as single NAL.        if (buffered_size + 2 + header_size + size <= s->max_payload_size &&            !skip_aggregate) {            if (buffered_size == 0) {
     //发送第一个数据包                if (codec == AV_CODEC_ID_H264) {                    *s->buf_ptr++ = 24;                } else {                    *s->buf_ptr++ = 48 << 1;   //hevc head flag  Header 为96 后面一般会跟VPS,PPS,SPS等信息，这些包字节少，可以放在一起一次发送VPS,PPS,SSP之间插入两个字节表示各类型包长度。                    *s->buf_ptr++ = 1;                }            }            AV_WB16(s->buf_ptr, size);            s->buf_ptr += 2; //数据包长度（两个字节表示）            memcpy(s->buf_ptr, buf, size);            s->buf_ptr += size;            s->buffered_nals++;        } else {            flush_buffered(s1, 0);            ff_rtp_send_data(s1, buf, size, last);        }    } else {        int flag_byte, header_size;        flush_buffered(s1, 0);        if (codec == AV_CODEC_ID_H264 && (s->flags & FF_RTP_FLAG_H264_MODE0)) {            av_log(s1, AV_LOG_ERROR,                   "NAL size %d > %d, try -slice-max-size %d\n", size,                   s->max_payload_size, s->max_payload_size);            return;        }        av_log(s1, AV_LOG_DEBUG, "NAL size %d > %d\n", size, s->max_payload_size);        if (codec == AV_CODEC_ID_H264) {    //视频类型为H264            uint8_t type = buf[0] & 0x1F;            uint8_t nri = buf[0] & 0x60;            s->buf[0] = 28;        /* FU Indicator; Type = 28 ---> FU-A */            s->buf[0] |= nri;            s->buf[1] = type;            s->buf[1] |= 1 << 7;            buf  += 1;            size -= 1;            flag_byte   = 1;            header_size = 2;        } else {            uint8_t nal_type = (buf[0] >> 1) & 0x3F;  // For hevc             /*             * create the HEVC payload header and transmit the buffer as fragmentation units (FU)             *             *    0                   1             *    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5             *   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+             *   |F|   Type    |  LayerId  | TID |             *   +-------------+-----------------+             *             *      F       = 0             *      Type    = 49 (fragmentation unit (FU))             *      LayerId = 0             *      TID     = 1             */            s->buf[0] = 49 << 1; //98只是Header，并不是真正意义上视频包类型。            s->buf[1] = 1; //固定不变            /*             *     create the FU header             *             *     0 1 2 3 4 5 6 7             *    +-+-+-+-+-+-+-+-+             *    |S|E|  FuType   |             *    +---------------+             *             *       S       = variable             *       E       = variable             *       FuType  = NAL unit type             */            s->buf[2]  = nal_type; //该字节才表示真正意义上的数据类型            /* set the S bit: mark as start fragment */            s->buf[2] |= 1 << 7;  //第一个数据包分片            /* pass the original NAL header */            buf  += 2; //去掉两个字节的头            size -= 2;            flag_byte   = 2;            header_size = 3;        }        while (size + header_size > s->max_payload_size) {
    　　　　　　//中间数据包分片            memcpy(&s->buf[header_size], buf, s->max_payload_size - header_size);            ff_rtp_send_data(s1, s->buf, s->max_payload_size, 0);            buf  += s->max_payload_size - header_size;            size -= s->max_payload_size - header_size;            s->buf[flag_byte] &= ~(1 << 7);        }        s->buf[flag_byte] |= 1 << 6;//最后一个数据包分片        memcpy(&s->buf[header_size], buf, size);        ff_rtp_send_data(s1, s->buf, size + header_size, last);    }}

 

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