[TOC] ## 概述 DESCRIBE 命令用于請求指定的媒體流的 SDP 描述信息 關于 SDP ( Session Description Protocol,會話描述協議) 請參考 [RFC 2327](https://rfc2cn.com/rfc2327.html). ## 格式 請求頭 | 頭字段 | 描述 | | --- | --- | | Accept | 列出客戶支持的內容類型 (application/sdp is the only supported type). | 響應頭 | 頭字段 | 描述 | | --- | --- | | Content-Type | 內容類型 (application/sdp). | | Content-Length | SDP 描述串的長度. | | Content-Base | 如果 SDP 描述串中使用了相對 URL, 這里是相關的基本 URL. | ## 示例 請求 ``` DESCRIBE rtsp://myserver/live.mp4 RTSP/1.0 CSeq: 0 User-Agent: Vision MC Accept: application/sdp Authorization: Basic cm9vdDpwYXNz ``` 響應 ``` RTSP/1.0 200 OK CSeq: 0 Content-Type: application/sdp Content-Base: rtsp://myserver/live.mp4 Date: Wed, 16 Jul 2008 12:48:47 GMT Content-Length: 847 v=0 o=- 1216212527554872 1216212527554872 IN IP4 myserver s=Media Presentation e=NONE c=IN IP4 0.0.0.0 b=AS:50064 t=0 0 a=control:rtsp://myserver/live.mp4&resolution=640x480 a=range:npt=0.000000- m=video 0 RTP/AVP 96 b=AS:50000 a=framerate:30.0 a=control:rtsp://myserver/live.mp4?trackID=1 a=rtpmap:96 H264/90000 a=fmtp:96 packetization-mode=1; profile-level-id=420029; sprop-parameter-sets=Z0IAKeKQFAe2AtwEBAaQeJEV,aM48gA== m=audio 0 RTP/AVP 97 b=AS:64 a=control:rtsp://myserver/live.mp4?trackID=2 a=rtpmap:97 mpeg4-generic/16000/1 a=fmtp:97 profile-level-id=15; mode=AAC-hbr;config=1408; SizeLength=13; IndexLength=3;IndexDeltaLength=3; Profile=1; bitrate=64000; ```