Generic RTP Payload Format for Forward Error Correction in Video - PowerPoint PPT Presentation

Generic RTP Payload Format for Forward Error Correction in Video Applications draft-bsong-avt-rtp-gfec-00.txt Hao Qin hqin@mail.xidian.edu.cn

Summary • Aim: – To reduce the impact of packet loss to a video receiver. • Solution: – Use FEC technique to recover the lost information from the correctly received packets. – Bundle maximum number of output data blocks from an FEC encoder into each RTP packet to maximize the bandwidth utilization and minimize the latency. 7/14/06 2

Unequal FEC protection • Different parts in the video stream may have different importance to the receiver. – reference frames are critical to a decoder to reconstruct following pictures. – prediction frames are used to reconstruct just one picture based on the previous reference frame. – Losses of reference frames may cause far more serious disasters to the video decoder because the video decoder may be forced into a very long time of interruption. • Data with different importance may be unequally protected with different FEC algorithms. 7/14/06 3

Interleaving • Many consecutive data blocks from an FEC encoder may be encapsulated into a single RTP packet, so that loss of an RTP packet means loss of many data blocks. This brings difficulty to an FEC decoder for the insufficient information to reconstruct the source data. • Interleaving should be introduced to solve this Interleaving should be introduced to solve this • problem. problem. 7/14/06 4

Interleaving Feed into interleaver N ... ... 0 1 K-1 K N-1 Output from interleaver ... ... N N+1 2K-1 2K 2N-1 V FEC units ... ... ... ... ... ... ... ... ... VK-1 VK VN-1 (V-1)N K A RTP A RTP A RTP A RTP A RTP packet packet packet packet packet 7/14/06 5

Generic payload format for FEC 0 7 8 15 16 23 24 31 RTP Header FEC FEC R C Interleaving index Block size type subtype One or more encoded data blocks …… R 3bits reserved C 1bit interleaving indication FEC type 4bits mapped to a particular FEC algorithm FEC subtype 6bits mapped to the FEC algorithm parameters Interleaving 10bit zero-based index within an interleaving index s group Block size 8bits number of octets in a data block 7/14/06 6

The process flow of the video stream Video FEC Interleaving Encapsulation encoder encoder FEC type C bit RTP FEC subtype Interleaving index Transmission Block size Block size Video FEC Payload Deinterleaving decoder decoder extraction 7/14/06 7

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