Quote:
Originally Posted by madshi
There are 3 clocks during video playback:
(1) System clock ("time").
(2) Video refresh rate.
(3) Audio hardware clock.
The system clock really doesn't have anything to do with video playback, but madVR uses it to measure and compare the other two clocks. Now it is possible (even probable) that the system clock is not perfect. But that's not a big problem because if it's e.g. slightly too fast, both video and audio clocks will be measured wrong in the exact same way, so everything's fine.
If the video and audio hardware clocks are "perfect", there should be no dropped or repeated frames (if your PC is fast enough). However, video and audio clocks are usually both imperfect. If both are imperfect in the same way (e.g. being 0.1% too fast), again there's no problem. But if the amount of "deviation from perfectness" of audio and video clocks is not identical then madVR has to either drop frames (video clock slower than audio clock) or repeat frames (video clock faster than audio clock) to make sure video and audio stay in sync.
The refresh rate as shown in the first line in the madVR OSD is madVR's measurement of the video clock, measured by using the system clock. The audio "deviation" in the madVR OSD shows how much the audio clock deviates from "perfectness", measured by the system clock. If e.g. the measured refresh rate is 24.24000Hz (1% too fast for 24.000 content) and the audio deviation is exactly 1%, too, then there should be no frame drops/repeats. If the video/audio deviation differs, there have to be drops or repeats.
Reclock replaces the audio clock. Through real-time audio resampling Reclock makes sure that the audio clock exactly matches the video clock. This way madVR doesn't have to drop or repeat frames. E.g. if the video clock is 0.1% too fast then Reclock makes sure that the audio clock is also 0.1% too fast. Things get more complicated if you ask Reclock to change the playback fps. In that case I would expect the measured audio clock deviation to be much bigger. E.g. if you play 24p content at 25/50Hz I would expect the audio deviation measurement to show a roughly 4% deviation because Reclock achieves the fps change by running the audio clock much faster or slower.
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Thanks for the wonderful answer. I better bookmark this so I won't forget where to look up when I want more details. Let's just see if I got this. Basically the problem with 24p@60Hz is that you need to find a way to make the Video and Audio clock to stay sync without the need of repeated or dropped frames. That's hard to do with ReClock because of the way it works (by changing not only the refresh rate, but the video fps as well). I may have got it wrong since this is all news to me but for now that's enough, thanks again.