On 02/08/2012 05:41 AM, David McGaw wrote:
The DTV signal coding has a major problem in that it is not
deterministic - they can't even synchronize the audio and video. There
have been many workshops on this at the Audio Engineering Society
conventions. I doubt there is any useable timing in it.
You are mixing up the issue of the relative timing between the picture
and audio (which is a mess at times) with the issue of having good
timing in the transmitted signal.
The signal is a very layered thing, where PCR has been mentioned.
The audio and video is compressed and encoded into a program stream.
Several program steams is then muxed together into a transport stream,
all according to the ITU-T H.222.0 spec. The PCR ticks in the universal
27 MHz rate (older MPEG-1 systems used 90 kHz).
The transport stream is then padded into fixed bit-rate, wrapped in
various ways and then transmitted using some modulation. For instance,
DVB-T uses a COFDM modulation. Using a combination of the COFDM
structure, pilot-tones, etc. fairly good frequency and fairly stable
phase should be retrievable. The absolute phase of the received phase
could be troublesome to find out.
Chances are that a GPS receiver is feeding you through the transmitted.
Many time-nuts have matching GPS receivers (such as a Thunderbolt)
already running for them.
Cheers,
Magnus
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