生成sdp文件
#define AV_BASE64_SIZE(x) (((x)+2) / 3 * 4 + 1) char *av_base64_encode(char *out, int out_size, const unsigned char *in, int in_size) { static const char b64[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; char *ret, *dst; unsigned i_bits = 0; int i_shift = 0; int bytes_remaining = in_size; if (in_size >= 0x7fffffff / 4 || out_size < AV_BASE64_SIZE(in_size)) { return NULL; } ret = dst = out; while (bytes_remaining) { i_bits = (i_bits << 8) + *in++; bytes_remaining--; i_shift += 8; do { *dst++ = b64[(i_bits << 6 >> i_shift) & 0x3f]; i_shift -= 6; } while (i_shift > 6 || (bytes_remaining == 0 && i_shift > 0)); } while ((dst - ret) & 3) *dst++ = '='; *dst = ' '; return ret; } void h264_sdp_create(uint8_t *file, uint8_t *ip, uint16_t port, const uint8_t *sps, const int sps_len, const uint8_t *pps, const int pps_len, int payload_type, int time_base, int bitrate) { char buff[1024] = {0}; char str_profile_level_id[100]; uint32_t profile_level_id = 0; if (sps_len >= 4) { // sanity check profile_level_id = sps[1] << 16; profile_level_id |= sps[2] << 8; profile_level_id |= sps[3]; // profile_idc|constraint_setN_flag|level_idc } memset(str_profile_level_id, 0, 100); sprintf(str_profile_level_id, "%06X", profile_level_id); char str_sps[100]; memset(str_sps, 0, 100); av_base64_encode(str_sps, 100, (uint8_t *) sps, sps_len); char str_pps[100]; memset(str_pps, 0, 100); av_base64_encode(str_pps, 100, (uint8_t *) pps, pps_len); char demo[] = "m=video %d RTP/AVP %d " "a=rtpmap:%d H264/%d " "a=fmtp:%d profile-level-id=%06X; packetization-mode=1; sprop-parameter-sets=%s,%s " "c=IN IP4 %s"; snprintf(buff, sizeof(buff), demo, port, payload_type, payload_type, time_base, payload_type, profile_level_id, str_sps, str_pps, ip); printf("h264 sdp: %s ", buff); remove(file); FILE *fd = NULL; if((fd = fopen(file, "wt")) > 0) { fwrite(buff, strlen(buff), 1, fd); fclose(fd); } }
h264.sdp文件
m=video 9832 RTP/AVP 96 a=rtpmap:96 H264/90000 a=fmtp:96 profile-level-id=640020; packetization-mode=1; sprop-parameter-sets=Z2QAIKzZQMApsBEAAAMAAQAAAwAyDxgxlg==,aOvssiw= c=IN IP4 10.143.44.169
"m=" ： video：媒体名称 9832：端口 RTP/AVP：传输协议 96：RTP协议中的pt值
"a=rtpmap"：96：RTP协议中的pt值 H264：视频编码 90000：视频采样率
"a=fmtp"：
profile-level-id：这个参数用于指示 H.264 流的 profile 类型和级别. 由 Base16(十六进制) 表示的 3 个字节. 第一个字节表示 H.264 的 Profile 类型, 第三个字节表示 H.264 的 Profile 级别
sprop-parameter-sets：SPS,PPS 这个参数可以用于传输 H.264 的序列参数集和图像参数 NAL 单元. 这个参数的值采用 Base64 进行编码. 不同的参数集间用","号隔开
packetization-mode：表示封包模式：0：单一 NALU 单元模式 1：非交错(non-interleaved)封包模式 2：交错(interleaved)封包模式
| Type | Packet Unit | Single Nal Mode | Non-Interleaved Mode | Interleaved Mode |
| 0 | undefined | ig | ig | ig |
| 1-23 | NAL unit | yes | yes | no |
| 24 | STAP-A | no | yes | no |
| 25 | STAP-B | no | no | yes |
| 26 | MTAP16 | no | no | yes |
| 27 | MTAP24 | no | no | yes |
| 28 | FU-A | no | yes | yes |
| 29 | FU-B | no | no | yes |
| 30-31 | undefined | ig | ig | ig |
"c=IN"：IP地址