I'm working on a very big, year long time-lapse project.
I have been filming in 4K at 15FPS to produce very long videos (~20-24 hours), which I have been speeding up either to 5,000%, 10,000%, 40,000% or 80,000% playback speed to produce videos which are roughly 20, 10, 2 or 1 minute long (depending on the length of the original footage). On the surface, this is relatively simple -just open the file and increase the playback speed to the desired duration. (Because the playback speed is capped at 10,000%, you might need to do it once, then export, then import the faster file and repeat, in order to get to the desired playback speed -I've done this a bunch of times with relatively good success...)
However, since the original is 15 FPS and that is a lower quality overall playback speed, I'd like to increase the FPS to 30 to match another raw video source. Given that I initially have way more frames in the 20 hour video at 15 FPS than would be needed to produce a 20 minute video that is 30 FPS, it seems that I shouldn't be sacrifing quality to get there.
However, I've noticed that when I increase the frame rate, the quality drops significantly. What can I do to preserve the original quality at the faster playback speed and the higher frame rate?
For the project I'm worknig on, I produce files that are 5,000% playback speed, then delete the original (they take up too much space to save). From that point forward, the version at 5,000% playback is what I have to work from. I may take all or parts of it and speed them way up, but with the original gone, that 5,000% playback version is my new "source" file. Therefore, it's especially important to maintain the highest possible quality in that first sped-up version, but also important not to just add extra file size with unnecessarily high bit-rate and longer encoding time.
Bonus Question: Since I'm only speeding up playback speed and increasing frame rate, without doing any color grading or other fx, (that can come later) I'd think the encoding speed would be relatively fast. Sometimes it takes several hours, just for one video. Is there anything I can do which will help me speed things up? I'm already working on a better hardware approach, but from a process perspective, what would help? Is Media Encoder even the fastest tool, or is there a better one which would more quickly achieve what I'm trying to do? I'd also be thrilled to find a batch file converter that could speed up multiple videos using the same settings (rather than queing up one video at a time and clicking through the same menus over and over just to select the same settings) -especially if that tool encoded faster and preserved quality.
Side note: I understand that it would be better to capture still images, color grade them in lightroom, then import them to Premiere and convert them to a video. Due to the system I'm using to capture the footage, that is not currently an option.
Another side note: These videos should have no audio track, so I usually turn that off with the assumption that it will save on file size and encoding duration -is that an accurate assumption?
One option is to try After Effects. You can Enable Time-Remapping and drag the keyframes to get very high playback speed. Regarding quality: are you interpreting the clip to play at 30fps instead of 15? Ie. via the Modify>Interpret Footage dialogue? If so there should be no quality loss providing you put that clip onto a 30fps sequence that matches the resolution and export in a 'high quality' codec such as ProRes.