Program Feed Stutters When Source Footage & Sequence Frame Rate Are Different

Report · Aug 25, 2023

I've been having this issue for some time and recently identified the source of the problem. We shoot AVCHD 1080p 59.94 fps and edit in a 1080p 29.97 fps sequence, and this results in the footage stuttering/skipping every few seconds in the Program Preview. If I put the footage in a 59.94 fps sequence it plays back smoothly, so the problem seems to be the mismatched frame rates.

I've tried using the built in presets for AVCHD footage as well as making my own custom sequence and the result is the same: If the sequence fps does not match the source fps the Program Preview will stutter. I've also noticed it's worse when using 1/2 or 1/4 playback quality, but still happens even at Full quality.

Why would this be happening? It seems like a bug in Premiere because it should be able to provide smooth previews with mismatched frame rates. My PC specs are below and they should be more than capable of handling these video clips and previewing them properly.

Any help or suggestions would be appreciated because this issue makes it very difficult for us to tell if our footage is jumpy or it's just Premiere previewing it incorrectly.

UPDATE: I did figure something out though and I think it may be related to GPU accelrated playback in the Project Settings. I noticed in Task Manager that my RTX 3060 usage was spiking at the same time the stutters were happening. The GPU usage slowly climbs from 0% to 20% then spikes to 30% when the stutter occur.

When I switched to Software Only rendering the stutters appear to stop. CPU usage goes up, GPU usage stays around 30%, but no stuttering.

Obviously this is a workaround and not a solution, as is transcoding or using a 60fps sequence. I guess I'll have to contact Adobe directly unless someone comes along with a solution.

Premiere Pro v. 23.6.0 (Build 65)

Windows 10 Pro 64bit

Intel Core i9-13900K 3.00 GHz

64GB DDR4 RAM

MSI MPG Z690 EDGE WIFI DDR4 mobo

RTX 3060

WD BLACK SN850X NVME scratch

WD BLACK SN750 SE NVME boot/install

Report · Aug 25, 2023

Hello RyanShepard,

You haven't given much info about the technical details of your footage. I recommend reviewing the supported file formats documentation:

https://helpx.adobe.com/ca/premiere-pro/using/supported-file-formats.html

Strictly speaking, any effect applied to footage will increase the demands on your hardware. This includes any mismatch between clip format and sequence settings. A frame rate mismatch means you are asking Premiere Pro to do a frame rate conversion of your clips.

Also, what sort of render indicators are you getting in the timeline?

"A red render bar appearing in the time ruler of a sequence indicates an unrendered section that probably must be rendered to play back in real time and at full frame rate. A yellow render bar indicates an unrendered section that probably does not need to be rendered to play back in real time and at full frame rate. "

https://helpx.adobe.com/ca/premiere-pro/using/rendering-previewing-sequences.html

R.

Report · Aug 25, 2023

If you transcode the 1080p59.94 AVCHD to ProRes 422 LT (a "Smart Rendering" CODEC), it should play much better in a 29.97 Timeline.

Report · Aug 25, 2023

I've attached a screen grab from MediaInfo of a source file from the camera. It's an .MTS wrapper, which according to that link has native support.

The render indication is Yellow in the timeline and no effects have been applied to the footage.

I did figure something out though and I think it may be related to GPU accelrated playback in the Project Settings. I noticed in Task Manager that my RTX 3060 usage was spiking at the same time the stutters were happening. The GPU usage slowly climbs from 0% to 20% then spikes to 30% when the stutter occur.

When I switched to Software Only redniger the stutters appear to stop. CPU usage goes up, GPU usage stays around 30%, but no stuttering.

I know there have been issues in the past with Nvidia drivers, but I'm not sure there's still a problem and what the best driver package currently is. I am currently on Studio Drivers 539.99.

Report · Aug 25, 2023

Transcoding all the footage we use prior to editing would be a huge increase to editing time as well as storage space, so it's not really an option for us unless it's absolutely necessary. At this point I see no reason why the hardware shouldn't be able to play back our footage natively.

Report · Aug 25, 2023

The reason Warren suggested t-coding to ProRes is that AVCHD uses a long-GOP codec, H.264. An actual frame recorded to file every so often, but in between just data sets of the 1) pixels that have changed since the last complete i-frame, 2) pixels that will change before the next i-frame, and/or 3 BOTH.

So it isn't just playing back sequential frames. The computer has to compute up to 30 frames or more at a time before it can play them back. For a video player, this ain't so bad. Within an NLE, this is a load on top of the overhead of all the computations of image changes, grabbing bits of video clips from here & there on the computer, processing multiple tracks of audio ... yea, it's a struggle.

And then, you're shooting in 59.94, and telling it to playback in 29.97 ... probably thinking this is just a display time difference, right? But Premiere again has to computer the data from the AVCHD files in "real" time, then apply the change in playback rate. A LOT of extra computing.

For an intraframe codec like ProRes or a DNx, that's a ton easier. It's just a sequential group of lightly compressed but complete frames to play back, and changing the speed is easy.

Report · Aug 25, 2023

ProRes files can be their own Preview (no yellow line). AVCHD cannot.

ProRes source in a Sequence with Previews set to matching ProRes (a "Smart Rendering" workflow) might take some time to transcode footage in preparation, but that's gained back later with faster (and smoother) editing, rendering effects, audio mixing, color correcting, exporting rough cuts, exporting fine cuts, exporting for delivery. At 1080p, this is a benefit even on workstations that are ten to fifteen years old.

1080p ProRes 422 LT requires about 700Mb per minute of storage space. For a frame independent format that performs well with or without hardware acceleration and maintains picture quality, that's very good.

If unwilling to transcode, I'd set the Timeline to p59.94 as well and save changing to p29.97 for exporting the fine cut.

Report · Aug 25, 2023

When I switched to Software Only rendering the stutters appear to stop. CPU usage goes up, GPU usage stays around 30%, but no stuttering.

Thanks for posting this info / update. Hopefully that solves things for you.

I will add my own support for what Warren Heaton and R Neil Haugen have said - long GOP (aka "interframe") compression formats are really not ideal for editing (the technology was originally designed for distribution ... and then camera makers got a hold of it). Something to bear in mind for future projects.

R.