@johnebaker So, an off topic (but related) question if I might.

I sometimes see the "jittery" (jumping) video that you mentioned in motion shots of TV movies streamed over the web that I record via screen capture.

I have experimented with capture frame rates to find the best way to minimize this during screen capture.

You can see a sample of my testing here, where certain frame rates miss entire frames of fast motion of a movie.

I am having trouble understanding the issue at a conceptual level.

First, the movies that I record are old film movies, which were recorded at 24 fps.

So it seemed to me that using a screen capture frame rate at 24 fps should capture each (and every) movie frame.

But, as you can see from my testing, it does not. Even when I "oversample" at 30 fps capture.

I'm confused by that. (Although, per my end note here, I found that this missing of frames was due to using the Look Ahead setting for nVidia Hardware Encoding.)

I don't know how the streaming service (in this case, Turner Classic Movies (or TCM.com)) are streaming movies.

I know that they aren't doing it like in the old days, where a projectionist mounted a film, and a TV camera captured the screen. (I actually saw that done when I was a kid in school during a field trip to a local TV station.)

I presume, in that case that I would record at 30 fps (US NTSC) and that the video would have been telecine'd. (And then I would have to extract extra frames.)

Clearly websites like TCM are using digital versions of the movies. I am guessing Blu-Ray versions.

In which case, given what you said, the website would be streaming interlaced video.

But my monitor is progressive.

So I wonder what is happening in the middle? Does my browser change the video from interlaced to progressive?

Or am I watching interlaced video on a progressive monitor?

If they are indeed using BluRay discs (or, more properly, BluRay files) to stream the movies, then some jitter during panning shots is unavoidable. (Indeed I see it on the screen while streaming, regardless of the speed of my Internet connection.) But also I can make it worse by not capturing each and every frame.

So any thoughts on the best frame rate to capture NTSC streamed film movies so as to not miss frames?

(As you can see in my testing, I capture every frame when I capture at 60 fps. But that makes for a very large file. I have found, by "hacking" (as opposed to deduction/induction) that I can get all frames if I set my monitor to refresh at 60 Hz (it goes as high as 75) and record at 30 fps with "Look ahead" disabled for my nVidia hardware encoder. (It seemed that the "Look ahead" feature wasn't looking closely enough at motion, and not adapting properly.) And I also had to increase the number of max B frames.)

@pmikep

Hi Mike.

So as to not go too far off topic I am going to say it depends on the broadcaster and the content being broadcast. For instance the BBC hosts all it's content on Amazon servers (as do a lot of other online broadcasters) but the broadcasts are not the same quality, or use the same internet protocols that Amazon Prime does for its streaming content. The BBC iPlayer for instance caps out at 1080x720p in live view but can download content to your PC for limited playback times with higher quality playback resolutions.

Also at your end you could find the feed capped depending on the download speed of your connection and the ability of your system to download the information packets and display them in real time. Try even streaming 8K content from YouTube and see what happens. Most internet content providers use progressive content for streaming. I don't say all simply because I haven't had experience of all sites.

Ray.

@pmikep

Hi Mike

. . . . I am having trouble understanding the issue at a conceptual level . . . .

It looks like you have issue 2, Pulldown, and possibly a 'dropout' as well.

Assuming the download is at 24 fps - or has been converted to 30 or 60 fps by the host the video has had its framerate adjusted to match the monitor framerate - usually 60 fps, ie- Pulldown. However 24 into 30 or 60 is not a nice round number, they are subjected to Pulldown.

When capturing from screen the capture is usually from the output frame buffer which contains the decoded image frame(s) to be displayed on the monitor, at 60fps if that is your monitor setting

The 30fps capture therefore has to drop frames ie simplistically it could take every other frame, in the example you have shown it appears a frame has been dropped - this could have been due to a transmission error or an error in the decode that dropped it.

Under ideal conditions, supposing capture is taking the odd number frames then for the 4 frames in your example it should capture

1,3,5,7

however as I said above a frame has been dropped* ie frame 5 so you get

1,3,7

at 60 fps capture there is less of a problem as 1 frame dropout would hardly be noticed, if at all.

* You may find if you repeat the 30fps capture several times it will capture the correct number of frames.

. . . . So any thoughts on the best frame rate to capture NTSC streamed film movies so as to not miss frames? . . .

As you can see from the above - there is no ideal capture rate.

HTH

John EB

Thank you Mike for a clear explanation. My camcorder was set to recording at 50p. I've just had a look at the available settings and there isn't an option for 25i - only 25p or 50i or 50p. Presumably I should set to 50i then?

@r-sanders

Hi

Which Sony camcorder do you have? I have 3 different models and they all have an Interleaved setting however it is not called that in one of them.

John EB

Thanks @johnebaker for your answer.

FYI, I think we can rule out transmission error as the primary problem because the missing frame problem occurred fairly repeatably.

And, as I said, it also seems to be a capture problem with b-frames. Which only muddies the picture (pun intended) as I focus on frame rates. (Another semi-pun.)

For now I've been lowering my screen refresh to 60 Hz and recording at 30 fps with as many b-frames as OBS allows (4) and with Look-Ahead off. It captured a waterfall scene and pan from Alfred Hitcock's Vertigo, and these settings gave me the best visually smooth movement.

(So, basically, I've been doing trial & error testing, without as much deduction/induction as I would like.)

@pmikep

Hi Mike

. . . . OBS . . .

Did you see this comment at the bottom of page 1 of the rather long topic about issues with OBS recordings and best settings?

John EB

No, I didn't. But I watch the stats in real time. The Stat page says no dropped frames. (Even at 60 fps.) My nVidia (and yours) completes a frame in less than 2 ms.

Still, I'll double check.

(I know about your favorite screen capture program. At this time, I'm too cheap to buy it.)

@johnebaker - I have Sony HDR-CX625