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Best frame rate to screen capture old TV movies streamed over the web?
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pmikep [Avatar]
Senior Member Private Message Joined: Nov 26, 2016 22:51 Messages: 284 Offline
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This question is primarily for JL_JL, since he seems to understand this stuff. And I was going to PM him this question. But I thought perhaps others might be interested in his answer. (I vaguely remember asking this before, but if I did, can't find it here. And I keep vacillating back and forth as to what is the right answer.)

I record old Noir movies that are either played on TV or, more recently, streamed over the web.

For the ones played on TV, I use whatever frame rate Windows Media Center gives me in its recorded file. I have no control over that.

For those streamed over the web, I use a screen capture program to record the movie playing full screen from my monitor.

I have my screen recorder set to 30 fps. (In part because of the 60 Hz refresh rate of my monitor. Although my new monitor refreshes at 75 Hz.)

Yesterday I was checking to see how much compression I could get away with in HEVC. (I am at a ridiculous 1000 kb lately, although the image quality seem okay to me. (Viewing later on a 52" TV screen.))

I was stepping through a high motion segment of a (film) movie and I noticed a bunch of "smearing" of small, but detailed, areas, like eyes, mouths.

(I can post a screen shot if anyone wants to see.)

I initially thought that I had too much compression. But changing the compression to ridiculously high Quality settings (that is, not much compression) didn't change the smearing.

That got me thinking that perhaps the smearing was caused by me not matching the original source material (film) in my screen capture.

Now, here's where I get confused. Many of the later movies that are streamed are streamed from a Blu-Ray disc. (In fact, they must all be digitized because it's not like a Projectionist has to mount a film when you call it up on the web to watch it.)

I read that Blu-Ray has a frame rate of 24 fps to match (film) movies.

I presume that the way that Blu-Rays are made is that a special machine steps through a (film) movie a frame at a time, scans a frame, and moves on to the next. (As opposed to playing the movie on a screen and recording it from the screen, as is done on TV with old movies. (Which I presume needs telecine and produces extra (duplicate) frames.))

If so, then by me recording a 24 fps movie at 30 fps, it seems to me that I would be getting a telecine type effect, where I am getting an extra frame in occasionally?

I have compared two screen recordings taken at 24 and 30 fps and it seems to me that the 24 fps is slightly better. But then it's not a double blind test and I could just be fooling myself.

Is there a definitive answer as to what frame rate I should be using for screen capture of film movies streamed over the Net?

This message was edited 2 times. Last update was at Dec 19. 2020 11:52

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pmikep [Avatar]
Senior Member Private Message Joined: Nov 26, 2016 22:51 Messages: 284 Offline
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I think that the answer is: 48 fps for a film movie.

I did a bunch of testing on a short clip of an Alfred Hitchcock movie, where there was some fast movement that caught my eye when it jumped on the big screen TV.

I tried screen capture frame rates from 24 fps (per my post above, to "match" the frame rate of the movie) to 60 fps, the highest that my screen capture utility allows.

I also lowered my monitor's fresh rate from 75 Hz to 60 Hz. (No difference that I noticed.)

It turns out that 24 fps is too slow, in that it sometimes misses some frames of a movie.

I made a short video demonstrating this. If the attachment won't open here, then this is a link to stream the video.

60 fps works, but is too fast in that there are a lot of duplicate frames. And, of course, 60 fps creates a larger file than 48 fps.

I am hypothesizing that the frames of an Internet streamed movie are not synced to anything at the receiving end. And so I've settled on 48 fps, which is 2 x 24 fps, to over sample the film, in order to catch all the frames.

There are still sometimes some duplicates this way. But not as many as at 60 fps capture. And no lost frames at 24 fps, per my short video. (I suppose it's a toss up if, perception-wise, an occasional duplicate frame causes stutter, vs a missing frame causing jerk.)

As a side note, I tried using PD 18 to do my frame by frame testing. I remember someone here saying that PD allows "frame by frame" editing.

If it does, I could not get that to work. What I found was that PD 18 gave me second by second editing. So I had to use another Editor that allows shuttling between frames.
 Filename
CL forum Frame Rate Screen Capture.mp4
[Disk]
 Description
A video showing missing frames
 Filesize
14121 Kbytes
 Downloaded:
5 time(s)
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pmikep [Avatar]
Senior Member Private Message Joined: Nov 26, 2016 22:51 Messages: 284 Offline
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A contributor here suggested to me in a PM that my question is better asked over at DigitalFAQ.com or Videohelp.com.

Which I will do.

But just for completeness, after sleeping on my proposed solution of 48 fps, it occurred to me that a frame rate of (Update) 24 fps should have captured all the frames in a 24 fps movie.

So that got me thinking about b reference frames. In my screen recorder utility, I had had "Look-ahead" enabled. Apparently the Look-ahead doesn't look closely enough, and did not provide enough reference frames for my short segment of quick motion.

So I went back to 24 fps for my screen capture and turned off "Look Ahead." I also increased the Max B-frames to (Update) 4. And that catches the fast motion in my little test.

Update: Nevertheless, for really fast motion, like a waterfall scene, I find that I have to record at 30 fps to avoid stuttering.

I don't understand why that is.

This message was edited 2 times. Last update was at Dec 28. 2020 13:18

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