Hello All
Any one having an idea till what are the values for Latency,JITTER &
Packet Loss that can be tolerated without sacrificing the quality of the MPEG-2
Video sent using MPEG-2 TS into UDP/IP.
An article Published on
http://www.broadcastpapers.com/tvtran/TandbergBroadband08.htm states the
latency has to be <= 500ns ......... is it ? cant the decoders developed
these days can tolerate more jitter ?
Just for your ref , some lines from above mention URL
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.5. Jitter and the MPEG-2 PCR
Embedded as a field in the MPEG-2 Transport Stream packet is a regularly sent
sample of a 27 MHz studio-generated timing reference. This is the Program Clock
Reference (PCR).
The PCR is carried as a 33 bit value transmitted typically every 40 ms for each
video/audio stream. Its main purpose is to act as a timing beacon for the
decoding process at the receive end. The PCR samples are used to maintain a VCO
(voltage controlled oscillator) inside the Receiver/Decoder to resynthesize the
original 27 MHz studio clock.
How this VCO is designed dictates how much PCR jitter that can be tolerated.
DVB specifies maximum jitter of ±500 ns - a fairly stringent demand but most
practical decoding implementations can tolerate much more jitter than this.
When mapping MPEG-2 TS packets into IP frames there is an inherent potential
problem since multiple TS packets are usually mapped into a single IP frame.
There will be an evenly distributed probability function of the TS packet
containing the PCR field appearing in either of the TS packets within one IP
frame. So, if you carry say 7 TS packets per IP frame and the TS packet period
is T then you will have an evenly distributed jitter histogram of width (7 *
T). The PCR resynthesize implementation in the Decoder will usually not have a
problem with this amount of additional jitter.
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Would highly appreciate if some one can provide the inputs on this issues
regards,
Prashant Desai
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