Happy Leap Day!
Today being February 29th, it makes sense to talk about time related to media files. Did you know that:
- TAI time, which is used in Precision Time Protocol (and therefore SMPTE ST 2110 systems) does not do anything different for leap days or even leap seconds. PTP uses a 48-bit count of seconds to represent the time elapsed since 00:00 (midnight) January 1, 1970.
- Fractional frame rates, like those used in North America, Japan, Brazil and a few other places work just fine with TAI. However, you need to be careful - to get the correct frame count for a particular time duration, don't use "29.97" or "59.94." These two numbers are only approximations of the actual frame rate. Instead, use the precise correction factor in calculation, which is 1000/1001. For example, a 720p signal in North America runs at an exact frame rate of 60,000/1001 frames per second, or 59.94005994005994005994005994006 frames per second. When you are working with billions of frame times since 1970, accuracy counts!