Still duration timing problem

Report · Mar 03, 2023

I was working on some stop-motion video and I noticed that the timing wasn't matching outside references. Specifically I had set the still image default duration to 0.5 seconds. This should have matched a metronome speed (or music beat) of 120 BPM. But it would get noticably out of sync after just a few beats. So I made a test video with just 4 images of "1", "2", "3", and "4" repeating in a loop. And I found that the stills were advancing at approximately 129 stills per second! This is much faster than I can account for with a 0.5 second still duration.

My frame rate is 29.97 fps so each still should last 14.98 frames. But the difference between my expected 120 stills per second versus the actual 129 stills per second is more than you could account for with just rounding error in the framerate. So what am I doing wrong? How do I get my stills to march out at a specific expected rate?

Thanks in advance.

Report · Mar 03, 2023

First, nothing can be in partial frames. So a still can be 14 frames, it can be 15, but it cannot be 14.98 frames.

Any particular reason for the 29.97 sequence?

Neil

Report · Mar 03, 2023

29.97 fps is a standard broadcast frame rate in North America so I just took the default. But as I said, a fraction of a frame is not enough to account for the error. 29.97 fps is also a standard camcorder speed - if you were recording a 120 BPM metronome on a camcorder it wouldn't speed it up or slow it down by much.

How reliable is the Still Duration setting - is it just a nominal figure or is it meant to be precise? I can imagine things that would slow it down - for example the default transition duration seems to be stuck at 2 frames, but if anything wouldn't that add time, trather than speed it up?

Report · Mar 04, 2023

Dont forget to set

to desired framerate.

Default transition duration is not stuck at 2 frames it is the minimum requirement to set a double sided transition.

Report · Mar 04, 2023

How exactly does Intermediate Media Timebase affect this?

In general, I've had a hard time getting clear answers to anything about timing in Premiere Pro. Out there on the web there's a lot of "folk culture" about things like this ("try this", "try that"), but there's no reason why it shouldn't be mathematically deterministic: If I have a set of still frames that I want to render at a precise rate (so they match a musical beat) it should be straightforward to compute the settings based on fps, still-duration, transition duration, timebase, etc. Where can I get some precise information on this?

Report · Mar 04, 2023

Still images don't have a framerate just a duration.

In video 1 frame is the limit.

In audio you can go as far as 1/48000 of a second.

the higher you set your sequence framerate the smaller 1 frame in time gets and the more accurate you can edit to the beat.

Sorry Intermediate Media Timebase is for still image sequences only (it sets the timebase).

Report · Mar 04, 2023

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.

Report · Mar 04, 2023

There are a lot of video production folks that would LOVE to kill 'fractional' framerates ... like 23.976, 29.97, 59.94 etc. And go to "straight" 24, 25, 30, and 60fps.

Then some like Warren here will say but that isn't possible with broadcast use. I've seen some intense discussions about this online and in-person at NAB. Where some highly tech types insist that with some changes, it would be possible. It's like the old full/legal range thing for Rec.709. Silly we still have it, but ... there it is, and you need to understand how it's designed to work from a practical self-defense stance.

One reason some music vids are "60" fps is simply as Ann notes, it allows a bit tighter cut to the beat. Especially considering there will normally be imperfect latency between image/sound on most devices, the reality is ... most users will not be able to note something is "off" if you're close mostly enough to begin with.

So it's like a lot of color work, my "specialty". There is not in existence a PERFECT presentation of any image created by any system/device. In that all other presentations are WRONG.

As long as there's no visual data loss, there are only displays of an image you like better or less. And I do mean no perfect ArriRAW-to-X space exists ... or Red or Sony S-log3.cine transform or LUT or whatever.

In video/audio work, latency is always a bit of the un-appreciated elephant in the room.

Neil

Report · Mar 04, 2023

<<for example the default transition duration seems to be stuck at 2 frames, but if anything wouldn't that add time, trather than speed it up?>>

No, the time is set by the length of the clips next to each other. You could have to 5sec clips next to each other and the time is 10 seconds. If the clips were stills or video with extra frames (head/tails) you are cutting off (at least where they join) then you could add a transition and it doesn't change the length of the sequence / timeline. Just what's showing.

<<shouldn't be mathematically deterministic>> Be an artist/editor too.