Still images don't have a framerate just a duration. But you're still creating a video and a video has a framerate. So I want to understand the relationship between them. As Neil Haugen said, above, "So a still can be 14 frames, it can be 15, but it cannot be 14.98 frames." That's obviously true but how do we confron it? Since there are no fractional frames let's assume PP will default to 14. The ratio of 15/14 is 1.07. 128 (my more precise actual output speed) /120 (my expected speed based on 0.5 second still duration) is 1.066, so this looked promising. So I started tweaking my Still Duration time up. It only gives you 1 digit to the right of the decimal point to play with and the best I got was 118.9 BPM at 0.52 seconds Still Duration. Closer, but no cigar. Premiere Pro also lets you set Still Duration by frames. 29.97 fps is close to 30 fps so I set it to 15 frames. That produced 120.7 BPM, the closest yet. But this comes back to Neil's question of "why 29.97?" Why indeed? Neil is one of our most experienced members, so I assume he already knew it was an industry standard and he was just asking rhetorically. But it's relevant here. Because it's surprisingly hard to find a Premiere Pro canned sequence that doesn't use 29.97 even when it calls it "30", e.g., DSLR 1080p30 is really 29.97 and most videographers say things like "30" or 24" when we really mean 29.97 or 23.976. But to get this to come out spot-on at 120 BPM I need a frame rate of exactly 30 fps. So I made a custom sequence from the DSLR1080p30 which I called "DSLR1080pTRUE30" and using that and a 15-frame still duration I got 120.2 BPM. So the answer to my question appears to be to use a still duration measured in FRAMES and to set a custom framerate to fine-tune it to the target speed. Care should be taken to anticipate all the musical demands of the piece since the frame duration can only be in integers. 120 BPM is a common tempo for popular music, but lots of club/rave music is 140 BPM. To accomodate both in the same piece a frame-rate of 70 fps could be used - non-standard but doable.
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