What's the best digital video option for a 16 frame per second movie?

December 19, 2014 9:23 AM

Is there some standard set of frame rates for digital video files? I have some video from 8mm film scans, the source is 16 frames per second. How should I convert them with Handbrake to play on standard computer players?

I had a bunch of 8mm film scanned. The service gave me two files per reel; an honest 16 frames per second source and a version with every other frame doubled so it looks fine played at 24 fps. (See ffprobe info). I tried using Handbrake to convert the 16 fps source to video marked 15 fps, and while it plays back correctly in VLC it plays back way too fast in Quicktime on the Mac. And note I said 15 fps; Handbrake has a menu with only a few selections for FPS, there's no free entry field and no 16 fps option.

Handbrake on the 24 fps frame-doubled version results in MP4 files that look and play fine on my devices. But they're bigger than necessary and it bugs me that I can't make a video file at an arbitrary frames per second. Video files can be arbitrary width and height, is there some restriction on frames per second? (FWIW these are vacation reels, not fine photography. I'm OK with a bit of infidelity for convenience.)

My target players are Quicktime, VLC, Plex on a Roku, and an iPad. I've got a solution that works but is not optimal and now I'm curious about digital video and restrictions on FPS.

posted by Nelson to Computers & Internet (6 answers total)

Doesn't handbrake have a "same as source" fps option?
posted by Monochrome at 11:56 AM on December 19, 2014

Response by poster: Handbrake does have a "same as source" option. Unfortunately my 16 fps source is marked as 24 fps, some sort of compromise that is a result of the scanning service's equipment. (My memory is they told me it's a German scanner and labels everything 25 fps (PAL), they fudge it to 24.)
posted by Nelson at 12:28 PM on December 19, 2014

If it helps at all, the 24fps version you have is not likely to be much bigger at all than a 16fps version of the same video, with every other frame repeated. Video compression is very complicated, but modern compressors only compress frame-to-frame differences (like h264 AVC). So, if frames repeat exactly, you may be sacrificing less than 1%-- or maybe even nothing at all, rather than a 33% gain you may imagine from tossing out every redundant frame. If you really want to get "into" a video that has contradictory/misleading/wrong information, you will need a non-user-friendly encoding solution, or one that trusts the user MORE than the data inside the file, and allows you to change or reprogram values.

If you want to dive further into it, I would suggest using a command-line encoder like MEncoder, but these are quite hard to use.
posted by Maxwell_Smart at 1:01 PM on December 19, 2014

Response by poster: I'd expected the 24fps version to not be much bigger than the 16fps either, but it doesn't turn out that way. Using Handbrake's "Normal" preset, constant quality factor RF 20, the frame doubled 24 FPS version is pretty much exactly 1.5x the filesize of the 16 FPS version. I can't explain it.

While I'm here threadsitting, Apple's Final Cut Pro docs suggest there just a few standard frame rates for digital video. And this StackExchange question strongly discourages someone from using "non-standard" framerates. Is that really correct? Do standards like H.264 allow oddball framerates and players just not handle them well? Or are they not even possible in video standards?
posted by Nelson at 1:34 PM on December 19, 2014

Best answer: The standards do support them. But I think players often use hand-tuned algorithms to convert between specific framerates. It's tricky to do this in a way that doesn't introduce very noticeable artifacts. And sources that aren't a standard framerate are rare enough that if a player doesn't support them it won't affect very many people.

I don't think it's really conceptually more difficult to convert framerates than it is to convert resolutions, except:
1) jittery or smeary motion seems to be more distracting than blurriness or blockiness.
2) Our framerates seem to be closer to the minimum we can get away with. Doing a good job of resizing really low res stuff like icons or game sprites is also difficult. We don't mind the blockiness so much, but going from a 16x16 icon to 24x24 is still pretty hard.
posted by aubilenon at 4:03 PM on December 19, 2014

Response by poster: I ended up asking this question on StackExchange where I got basically the same answer as aubilenon gives here. It may be possible to encode video marked with oddball frame rates, but there's no guarantee a player will play it back correctly.
posted by Nelson at 5:14 AM on December 26, 2014