faq	LTC / VITC Priority

The message was:
I also have another issue with this customer - not a big problem, though(!). Some tapes have both LTC and VITC. As he has both connected simultaneously, this causes a problem, as it sometimes switches from one to the other unexpectectly.

This might happen, if the VITC reader has problems reading timecode continously. Using VHS tapes, this is a known behavior, because the drop-out rate with this media is relative high.

In the mixed register, there is an automatic algorithm that normally reads VITC, but drops back to LTC, if there is a problem. This is a good idea, if both VITC and LTC are recorded synchronously with the same timecode values, but is not, if the timecodes are recorded independendly.

I suggested using an external switch, however he would like to select this software-wise.

There are different ways to solve it by software. First, it's possible not to use the mixed register, bit the timecode-specific LTC and VITC reader registers. In that registers, only the specified type of timecode is read, without switching to another source.

Another way is to switch off the unused type of timecode as a source for the mixed register. This is done by the command pclMixedEnable() (command $20). E.g. if you want to read VITC, and ignore LTC, enable the VITC reader and disable the LTC reader with the command pclMixedEnable(hdl, PCL_RMASK_VITC).