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

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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.

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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.

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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.

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Interleaving

A RTP packet

1

...

K-1 K

...

N-1 N N+1

...

2K-1 2K

...

2N-1

... ... ... ... ... ... ...

(V-1)N

...

VK-1 VK

...

VN-1 K N V FEC units

A RTP packet A RTP packet A RTP packet A RTP packet

Feed into interleaver Output from interleaver

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Generic payload format for FEC

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

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The process flow of the video stream

FEC encoder Interleaving Encapsulation Video encoder RTP Transmission FEC decoder Deinterleaving Payload extraction Video decoder

C bit Interleaving index Block size FEC type FEC subtype Block size

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