H.264 is divided into two parts: VCL and NAL VCL: refers to the part of how to perform a pure video stream of video compression algorithms, which is not described here (here is part of the big company) NAL: means a network abstraction layer part (NetWork Abstract Layer Units), is white to join a header for each sequence; convenient for network transmission. For example, if we send a courier, the VCL refers to something you want to mail, NAL is your box and mail order information, and the RTSP here is a courier company. Summary: People who do encoders care about the VCL section, people who do video transfer and decoding players are NAL sections. Some concepts: IF: Non-reference frame, generally the first frame B frame: All frames are made reference P frame: only the previous frame pixels --> Code stream: Pixel-macroblock - Splice - Frame - Sequence - Codestream Sequence (SEQENCE): LSPS (14 bytes) + LPPS (4 bytes) + LSEI (5 bytes) + 1i Frame + Several P Frame One Sequence is a comparison of frame rate; such as frame rate is 30Hz, then this sequence is 1I frame + 29 P frames. The code stream of the H.264 is actually a plurality of SEQENCE, SPS, PPS, and SEI describe the image information of SEQUENCE, I frame is a key, lost I frame this sequence is abolished, each sequence has only one I frame . Separator: Sequence parameter set and image parameter set in NAL will have a splitcher of 00 00 00 01; Profile: This parameter is included in the PSP, mainly to define a collection of encoding tools (which algorithm used Level: Mainly a key parameter, value range of the code stream. For example, the resolution RTSP Overview RTSP (Real Time Streaming Protocol), the reference criteria is RFC2326, and the RTSP protocol is based on text-based real-time streaming protocol, which is TCP / an application layer protocol. Graphical transmission process
RTSP message format
1 Request 2 response message format (Response)
C (Client) and S (Server) interactive flow chart in RTSP
4, RTSP key field description
4.1 Keywords: Options Get the available methods provided by the server (Option, Describe, Setup, Teardown, Play, Pause, Scale, Get_Parameter, Set_Parameter).
4.2 Keywords: Describe request flow SDP information. Note: You need to know how H264 Law Data generates SPS PPS information.
4.3 Keywords: Setup Client Reminder The server establishes a session and establishes a transfer mode. Note: This is determined here that RTP transmission interactive uses TCP (connection) or UDP (no connection) mode.
4.4 Keywords: Play Client Sends a play request. Note: This is introduced into the RTP protocol and the RTCP protocol.
4.5 Keywords: pause play pause request. Note: This keyword is often used in the recording playback, and the real-time video stream is almost not used.
4.6 Keywords: TEARDOWN Client Send Close Request
4.7 Keywords: GET_PARAMETER Gets parameters from the server, currently getting time parameters (scalable)
4.8 Keywords: set_parameter gives the specified URL or stream setting parameter (scalable)
Step 4 of the flowchart The following is the transmission of RTSP to encoding good H.264, take a subcontract transmission method, the RTSP transmitted by the RTSP is 1400 (NALU_SENT_LEN) one byte, first to call VENC_SENT At the time, it is necessary to pass the length (NAVFRMLEN), where there is a timestamp_increse, data TIMESTAMP_INCRESE in the same frame is the same, two frames of space algorithm: timestamp_increse = (unsigned int) (90000.0 / 25) here 90000.0 is the clock frequency of H.264, 25 is a frame rate. The interval of these two frames is 3600; in the part of a pack of data heads, there is a RTP_hedr: There is a Marker to be tagged, in one frame is divided into a multi-package transmission, only the last package marker = 1, front Other bags are equal to 0;
4.9 RTSP status code status-code = "100"; Continue | "200"; OK | "201"; create | "250"; low on storage space | "300"; multiple choices | "301"; MOVED Permanently | " 302 "; Moved Temporarily |" 303 "; See Other |" 304 "; NOT MODIFIED |" 305 "; Use Proxy |" 400 "; Bad Request |" 401 "; Unauthorized |" 402 "; payment request |" 403 " Forbidden | "404"; NOT FOUND | "405"; Method Not Allowed | "406"; Not Acceptable | "407"; Proxy Authentication Required | "408"; Request Time-Out | "410"; gone | 411 ";" 412 "; precondition failed |" 413 "; Request Entity Too Large |" 414 "; Request-Uri TOO LARGE |" 415 "; unsupported Media Type |" 451 "; parameter not understandtood |" 452 " Conference Not Found | "453"; Not Enough Bandwidth | "454"; Session Not Found | "455"; Method Not Valid in this State | "456"; Header Field Not Valid for Resource | "457"; Invalid Range | "458"; parameter is read-only | "459"; aggregate operation not allowed | "460"; "460"; ONLY AGGREGATE OPERATION Allowed | "461"; unsupported transport | "462"; Destination Unreachable | "500"; Internal Server Error | "501"; Not Implement | "502"; BAD GATEWAY | "503"; Service Unavailable | "504"; Gateway Time-out | "505"; RTSP Version Not Supported | "551"; Option Not Supported | Extension-Code Extension-Code = 3Digit Reason-Phrase = *
