Hi,
The actual origins of 30, 29.97, 25 fps, interlaced and progressive goes back to the 1940s. Originally frame rates were based on the electrical system frequency (60Hz in the US and 50Hz in Europe) and the different systems became known as NTSC and PAL.
NTSC was originally 30fps (half of the 60Hz mainss frequency) in black and white but altered fractionally when the Color sub-carrier was implemented around 1953 and the refresh rate became 59.94, and the frame rate became 29.97.
Some cameras do actually record at 30fps but more commonly the 30fps is a "nominal" expression - it's easier to say and write than 29.97fps!
Interlaced and progressive refers to the way the individual frames are produced, and again is based on the old refresh rates and scanning technology for CRT TVs and monitors - interlaced means that alternate scan line are recorded as 1 "half frame" and then combined with the "other half" to make a full frame, and progressive is recorded as a single full frame.
The drop frame timecode was introduced to compensate for the tiny difference between 29.97 and 30 which will eventually add up to a timing problem, which broadcasters needed to solve for real time scheduling.
Variable Frame Rates, in relation to recording, are a characteristic of the camera, and are a means of allowing the camera to record at different rates depending on context. Smartphones are well known for variable frame rates, often down as low as 5fps!
Forcing a VBR recording @5fps into a 29.97fps timeline is a challenge!!
So, to all intents, the frame rate conflict message in PDR is ignored by most folk, as it is usually a "technicality", if it becomes irritating, it can be switched off in Preferences>Confirmations.
These links are useful reading for further detail :
https://www.manchestervideo.com/2013/10/16/quick-guide-to-video-frame-rates/
https://www.borrowlenses.com/blog/intro-to-video-frame-rates-and-frames-per-second-shooting-speeds/
http://www.bodenzord.com/archives/79
https://en.wikipedia.org/wiki/NTSC
Cheers
PowerDirector Moderator
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