Internet Streaming Media

Transcription

1 Internet Streaming Media Reji Mathew NICTA & CSE UNSW COMP9519 Multimedia Systems S Multimedia Streaming preferred for streaming System Overview Protocol stack Protocols + SDP S Encoder Side Issues Receiver Side Issues File Format : MP4 Video on Demand Video Streaming to Mobile (3G), Video Conf, TV MPEG SDP S COMP9519 Multimedia Systems Overview Part 2 Slide 2 Reji Mathew Introduction Protocol Stack Streaming video, TCP or? What are the reasons for your preference? Requirements for streaming video & audio? Or why not just stream over? File / Encoder fragment Video Draw IETF protocol stack for streaming video? At Sender & Receiver, show protocols for streaming over SDP SDP TCP TCP COMP9519 Multimedia Systems Overview Part 2 Slide 3 Reji Mathew COMP9519 Multimedia Systems Overview Part 2 Slide 4 Reji Mathew

2 Protocol Stack Explain the role or function of each IETF protocol? Why do we need,, SDP,? Header Fields For information read introduction of corresponding IETF RFC documents Next : quick overview of + The first twelve bytes (octets) are present in every packet. COMP9519 Multimedia Systems Overview Part 2 Slide 5 Reji Mathew COMP9519 Multimedia Systems Overview Part 2 Slide 6 Reji Mathew - System Overview compressed bit stream fragment Attach Header Time stamping Sequence numbering Payload ID Frame indication Source ID Reorder packets Identify lost packets Detect payload type Detect participants Packets to Frames Need some feedback on network performance Real-Time Control Protocol () Used in conjunction with Primary function feedback on quality of data distribution COMP9519 Multimedia Systems Overview Part 2 Slide 7 Reji Mathew COMP9519 Multimedia Systems Overview Part 2 Slide 8 Reji Mathew

3 Control information exchanged between session members by packets Five packet types defined packets begin with a fixed part Similar to data packets packets are sent periodically from all participants of a session multicast example packets are stackable compound packets concatenate multiple packets Usually sent over (same as ) Using a port number = _port + 1 packet types to carry control information SDES : Source description items sent by all session members includes a persistent identifier of sources in the session SR : Sender Report sent by active senders report of transmission and reception statistics RR : Receiver Report Sent by receivers (not active senders) report of reception statistics BYE : Packet to indicate end of participation APP : Application specific functions COMP9519 Multimedia Systems Overview Part 2 Slide 9 Reji Mathew COMP9519 Multimedia Systems Overview Part 2 Slide 10 Reji Mathew + : System Overview Further Protocols Enabling Streaming Video AMR Audio Synchronized Video and AMR Audio Presentation SDP Description packetize packetize Audio Video protocol for control over the delivery of data with real-time properties. IETF Request for Comments: 2326 COMP9519 Multimedia Systems Overview Part 2 Slide 11 Reji Mathew COMP9519 Multimedia Systems Overview Part 2 Slide 12 Reji Mathew

4 SDP v=0 o=mmvc IN s=camera ONE i=video stream for realtime surveillance u= e=rmathew@nicta.com.au (Reji Mathew) c=in /2 t=0 0 a=recvonly m=video /AVP 98 a=rtpmap:98 MP4V-ES/90000 a=fmtp:98 profile-level-id=1; config=000001b a=orient:portrait How to control streams Start, Stop, Pause, Fast Froward, Rewind internet VCR Solution Real Time Streaming Protocol Establishes and controls one or more continuous media streams - such as audio and video Similar in syntax and operation to HTTP/1.1 Client Server protocol Text based IETF RFC 2326 COMP9519 Multimedia Systems Overview Part 2 Slide 13 Reji Mathew COMP9519 Multimedia Systems Overview Part 2 Slide 14 Reji Mathew Protocol Operation Text based messages between client and server Messages can be : Requests s Example : Play Play Request (TCP/) Play (TCP/) Media Server / OK CSeq: 833 Date: 23 Jan :35:06 GMT Range: smpte=0:10:22-;time= t153600z PLAY rtsp://audio.example.com/twister.en /1.0 CSeq: 833 Session: Range: smpte=0:10:20-;time= t153600z COMP9519 Multimedia Systems Overview Part 2 Slide 15 Reji Mathew Client : Signal Timing Diagram Media Client DESCRIBE (SDP) SETUP (Video stream) SETUP (Audio stream) PLAY PAUSE Media Server TEARDOWN COMP9519 Multimedia Systems Overview Part 2 Slide 16 Reji Mathew

5 System Overview File Receiver / Encoder Side Issues -Buffering input packetize data -Error concealment -Inter media synchronization Sender Side Issues Video -Conforming to Network Bandwidth -Adaptive Rate Control -Error Resilience -Packetization strategy System Overview : Sender Side Issues Packetization Strategy Example : fragment and packetize video Must meet network MTU limits Example : MTU = 1500 bytes Packets larger than MTU will result in fragmentation Resulting in overhead for each fragmented packet Loss of one fragment will corrupt the whole packet COMP9519 Multimedia Systems Overview Part 2 Slide 17 Reji Mathew : Try to allocate a single VOP (frame) per packet If packet is greater than MTU then break into multiple packets Can break any where - arbitrary byte positions Best to break at GOB or slice boundaries COMP9519 Multimedia Systems Overview Part 2 Slide 18 Reji Mathew System Overview : Sender Side Issues Packetization Strategy (continued) Minimize number of packets required Less packets means less bits spend on packet headers Example : 20 byte Header 8 byte Header 12 byte Header Minimize dependency between packets So that even if one packet is lost, the next packet can still be decoded Example : use VOP boundaries to start / stop packets System Overview : Sender Side Issues Fragmentation Strategy Minimize dependency between packets (continued) VOP 1 VOP 2 VOP 3 loss VOP 1 VOP 2 VOP 3 VOP 1 VOP 2 VOP 3 COMP9519 Multimedia Systems Overview Part 2 Slide 19 Reji Mathew COMP9519 Multimedia Systems Overview Part 2 Slide 20 Reji Mathew

6 System Overview : Sender Side Issues Procedure to fragment and packetize live coded video or stored video. Goal try to packetize one Frame per packet 1. Calculate Max allowable size of frame : Max_FrameSize = MTU Where = _header + _header + _header 2. Find size of frame N from the bit stream : FrameSize 3. IF (FrameSize <= Max_FrameSize) THEN include video frame in one packet 4. ELSE Break Frame into multiple packets Best to break at GOB or slice boundaries Example break at a slice boundary to form 2 smaller packets 5. N = N + 1 : go back to Step 2 System Overview : Receiver Side Issues Buffering Input Data Number of Packets Constant Transmit Rate Packets Generated T N T B Packets Received Mean Receive Rate Time Received Data Played out Constant Play Out Rate T N : Network transfer delay T B : Buffer Delay COMP9519 Multimedia Systems Overview Part 2 Slide 21 Reji Mathew COMP9519 Multimedia Systems Overview Part 2 Slide 22 Reji Mathew System Overview : Receiver Side Issues Inter Media Synchronization Audio De-packetizer and Video De-packetizer and SR 1680 : 15:2:32.00 SR : 15:2:32.01 COMP9519 Multimedia Systems Overview Part 2 Slide 23 Reji Mathew Audio clock = 8000Hz (eg u-law) 1760 = = = Video clock = 90000Hz (eg ) = = Protocols Enabling Streaming The story so far, & SDP Examples : Video on demand, TV Next Session Initiation S - Session Initiation Protocol Example : multimedia conference initiation What is role or function of S? COMP9519 Multimedia Systems Overview Part 2 Slide 24 Reji Mathew

7 S Session Initiation Protocol (S) Another session control protocol IETF RFC Protocol that can establish, modify and terminate multimedia sessions. Applications telephony, multimedia conferences S, like, Uses text-based request/response transaction model Requests contain Methods and Header fields s include 3 digit status codes (eg 200 OK ) Is Transport layer independent Uses other protocols for media delivery (eg ). S S Methods INVITE, ACK, CANCEL : for setting up sessions BYE : for terminating sessions REGISTER : for registering contact information OPTIONS : for querying servers about capabilities INVITE User agent client initiates a session with INVITE Invitation can be accepted by a user agent server S invitations convey session descriptions that allow participants to agree on a set of compatible media types Offer/answer model ACK confirmation to INVITE COMP9519 Multimedia Systems Overview Part 2 Slide 25 Reji Mathew COMP9519 Multimedia Systems Overview Part 2 Slide 26 Reji Mathew S S supports user mobility With proxy servers to help route requests to user s current location Registration function allowing users to upload current locations for use by proxy servers File Format MPEG-1 & MPEG-2 content typically exchanged as files that represent a stream ready to be delivered Embedded absolute time stamps Fragmentation of media for some preferred transport Random Access could be difficult file format : MP4 What are the advantages of MP4 compare to stored MPEG-2 compressed video files? What is hinting in the context of MP4? What are some advantages of hinting, especially for streaming server operation? COMP9519 Multimedia Systems Overview Part 2 Slide 27 Reji Mathew COMP9519 Multimedia Systems Overview Part 2 Slide 28 Reji Mathew

8 MP4 : Main File Format Concepts The Media data is stored separately from Meta data Media data : Audio, Video samples Metadata : Data describing the media Examples : timing info, number of bytes required for a frame Timing information specified by relative numbers (durations) rather than absolute numbers Allows editing to be easier eg insertion of a new frame Able to store media data distributed over several files Use URLs to point to media data stored at various locations MP4 : Main File Format Concepts The Media data is stored separately from Meta data Timing information specified by relative numbers (durations) rather than absolute numbers Able to store media data distributed over several files Locating media data by means of data offsets and length information Metadata tables mapping media sample number to location in a file Support streaming protocols through optional hint tracks Metadata information for packetization and header data Example hints for streaming stored as a separate track COMP9519 Multimedia Systems Overview Part 2 Slide 29 Reji Mathew COMP9519 Multimedia Systems Overview Part 2 Slide 30 Reji Mathew MP4: Hinting No need to parse the coded media bitstream Media Server MPEG-7 System : Client Server architecture MPEG-7 Indexing & Searching: Semantics-based (people, places, events, objects, scenes) Content-based (color, texture, motion, melody, timbre) Metadata (title, author, dates) Search Engine sounds like, looks like Query target No need to perform fragmentation clip.mp4 Client No need to create headers Low server complexity Generic server design retrieve MPEG-7 Database Query List of matching content clip1.mp4 clip2.mp4 Request for Content COMP9519 Multimedia Systems Overview Part 2 Slide 31 Reji Mathew Media Server Streaming Media / COMP9519 Multimedia Systems Overview Part 2 Slide 32 Reji Mathew