Larry Scutta posted:
The delay exsists because the box buffers the data before displaying it on the screen - this is because of the way that MPEG works (by reflecting changes in the picture) and because of error correction.
The delay varies depending on the complexity of the picture, the signal quality and the performance of the hardware/software in the reciever.
There is more of a delay for DTT
than DSAT - despite the sateliite hop - because DTT has a slower data rate
No - the data rates on DTT and DSat are comparable Larry - though BBC One is not statmuxed on DTT in England and is a fixed data rate service to allow for regional opts.
The extra delay on DTT is probably a result of a second MPEG decode/code process.
BBC One Digital Network leaves TV Centre as a 9Mbs MPEG2 distribution link, is then permanently decoded to SDI in the English regional centres (and the National centres as well), passed through an SDI opt switch and then permanently recoded to approx 4-5Mbs MPEG2 for broadcast (emission rate)
There are thus two MPEG2 code/decode processes for the DTT feed (even for BBC London who still have an opt-switch permanently in circuit I believe), whereas there is only a single MPEG 2 code/decode in the BBC One England DSat chain (the decode being at the domestic receiver)
Given that MPEG2 for broadcast normally runs on a GOP of about 12-18 frames (I think) - there is at least that delay introduced by both the coder and decoder? That would be a second minimum per code/decode process?