Smooth 50p / PAL playback on 60Hz screens - how?

[Geoffrey Cox]

I work in PAL land and the latest project is in 1080p / 50 frames per second shot at 100 shutter speed (on a Canon C100). When I monitor on my external screen (just a decent flat screen TV) I can use the system prefs on my Macbook to change the external screen refresh rate to 50Hz - I monitor via HDMI straight from the computer's HDMI port to screen. I edit in Premier. When I do this, all on-screen movement is perfectly smooth and natural looking. However laptops are seemingly all set to 60Hz and when viewed on my laptop screen, the movement is jittery and not smooth (especially movement across the screen). The same happens when I change the refresh rate of the external screen to 60Hz.

So, the question is what is the best way to get smooth(er) motion on a 60Hz screen (which frankly is most of them)? Should I re-encode at a different frame rate and if so which one - 60p, 30p? Will this even help or will it create problems of its own re on-screen movement? It's all a real pain and irritating to see lovely smooth footage messed up like this. Of course the film will probably be viewed mostly online, streamed to people's laptops or other portable devices.

Thanks.

[Boyd Ostroff]

I recently captured some PAL tapes that I shot back in 2005, and was thinking it would be a problem viewing these on my monitors. But I was surprised to find that it played fine on four different screens bought here in the US - a 6 year old 15" Dynex (Best Buy), brand new 19" Insignia (also a Best Buy store brand), new 24" Samsung and new 24" Vizio.

My footage was 4:3 DVCAM 576 i50, and I connected these screens via component video from a Sony tape deck.Now that is a different matter from connecting a monitor directly to your computer, so I can see why that might be an issue. I use Final Cut Pro on the Mac, and while it can directly drive an external screen, the quality is not as good as using a hardware device. So I use a BlackMagic Ultrastudio Mini Monitor, which is a little box that connects to the computer with thunderbolt and provides an HDMI output. So, when I set it properly, it's actually sending a PAL image to the external monitor.

But the thing that surprised me is that all my newer screens are actually PAL compatible, which is something they don't even mention in the specs. My older LCD screens were NTSC only. Anyway, perhaps a better solution would be to use an external USB or thunderbolt device to drive the external monitor, and let it put the video in the correct format. The Blackmagic Mini Monitor is inexpensive, think I paid about $135 at B&H Photo, it's one of my favorite new toys and I use it with both my Mini and MacBook Air. It works fine with my legacy Final Cut Pro 6 as well as Final Cut Pro X. Also works with Blackmagic's own software, like Resolve.

[Geoffrey Cox]

Thanks Boyd. The thing is it isn't the external screen that is the problem - I can set this to 50Hz and everything looks fine. I do have Matrox hardware but can't actually use this as it can't cope with 50 frames per second footage but simply using the HDMI connection from my laptop straight into the screen works fine anyway.

The problem is when viewing the rendered video file on my laptop screen which is how most people will view it, and it doesn't look anything like as good due to the movement problem described and my own tests confirm that it is because computer screens are fixed at 60Hz (and as far as I know this can't easily be altered). So what I'm wondering is what I can do about this, presumably by converting the video in some way.

[John McCully]

I resided in NTSC land over the years shooting mostly 30p and 60p. I relocated to a PAL country, purchased a PAL cam and immediately noted the phenomena you are talking about. I did some research, identified the problem, returned that cam and henceforth I import NTSC cams much to the chagrin of my local camera store.

I don't know if there is a solution but serious hunting at the time did not uncover anything other than the approach above I have followed ever since. Now, of course, higher end cams enable switching between NTSC and PAL, some with an annoying nag message when you shoot other than the system in place where one purchased the cam. For me this is a deal killer and I continue to import to get around that major irritation. As they say forewarned is forearmed.

Good luck with finding a solution, and if you do please let us know. Wish I could be more helpful.

[Roger Keay]

Here's an idea that might work depending on the material you shoot. Convert the 50P program to 25P and change the frame rate property to 24P. Computers handle film frame rate playback so your program should reproduce without the jitter you report on laptops. You may experience some blurring depending on how the software converts 50P to 25P.

There are several caveats. First, 24P requires that you shoot the content as if you were shooting film. You have to limit the speed of camera movement (pans, tilts) and the speed that objects cross the screen or you will have motion artifacts. Second, 24P playback will increase the length of the program by 4% so a 30 minute program runs 31 minutes and 12 seconds. Third, audio playback will be 4% slow which lowers the pitch. You can get software to fix this problem so the audio track is adjusted to the correct pitch while not falling out of lip sync with the images.

I have not tried this approach but I can't see why it wouldn't work. It is just a variation on the long time European practice of running 24 fps film at 25 fps for compatibility with the PAL frame rate. In the broadcast case, the playback is 4% faster so the program is 4% shorter in time and the audio pitch has to be reduced by 4%.

[Guy Caplin]

Having spent several years wrestling with this problem, I have to tell you that there is no one solution that works for all material. You say that you are using Premiere so you have a few different options at your disposal. If it's talking heads, just drop your clips onto a 30 or 60 fps timeline. I do this all the time and it isn't apparent. If you have fast moving material (and I guess you have) you might try this.
Set up a 60 fps timeline. Select your clips and right click - Modify - Interpret Footage - Assume frame rate to be - then insert 60. Drop your clips on the time line and right-click - select Clip Speed Duration. Set to 120% and for Time Interpolation select Optical flow. Sometime it works quite well. Clearly, if you have a synch sound track, it might be best to import it separately.

[Guy Caplin]

I ran a test on some difficult graphics material and this method works exceptionally well, however, I got my maths wrong in my previous post. In the speed duration you need to set the speed to 83.33%. This gives such good results because the 'Optical Flow' Time Interpolation option appears to be replicating vector motion standards conversion i.e. Premiere appears to be creating new frames from adjacent frames by moving blocks of pixels rather than merging adjacent frames. (Vector motion is considered the best way to do standards conversion.) The downside of this method is that it takes a long time to render and the "Media Pending warning appears for some time afterwards. Note that if your original 50 fps clip contains cuts, they can appear as 1 frame half mix transitions. Usually these are not apparent played at normal speed but occasionally you need to remove an obvious one.

[Geoffrey Cox]

Thanks for the suggestion Guy. I tried simply dropping the material into a 60p sequence and it look bad. So I tried the more complex method but came up against two major problems. Firstly you cannot 'Interpret footage' from the timeline but have to do it from the clip menu which would mean going through the whole project that way which would be prohibitive. But as it is only a few clips that are the real problem I still tried it but when I tried to change the duration there was no optical flow option available. It turns out that it isn't available in Premiere in 15.0 (my version) but is in 15.1. But I am very loathe to upgrade in the middle of a project especially as it says that 15.0 projects are not directly compatible with 15.1. I guess I could modify the problem clips elsewhere and bring them back in. Actually come to think of it - would that even work? Could I modify the problem clips in some way then bring them back into the 50p timeline?

[Geoffrey Cox]

As an update on this pretty big issue for us working in 50z land I have found a solution of sorts (notwithstanding Guy Caplin's brilliant help in converting files for me - he has his own method which works almost perfectly!).

The answer using proprietary methods is to use the 'Best (motion compensated)' Retiming quality setting in Compressor (having changed the frame rate to 60p). I didn't change the video size so the Resizing filter option isn't relevant. The problem with this is that converting to H.264 (for the web) takes too long using this setting (I mean days) so I found that using the X.264 codec instead (free download) produces as good results in much, much less time. It also has the advantage of not changing the colour space like H.264. The 10 minute film still took 4 hours to render but it was worth it - it looks pretty smooth at 60p and better than any other method I tried by miles (though still not quite as good as Guy's method it has to be said).

Larry Jordan gives info about X.264 here: https://larryjordan.com/articles/com...improve-video/

[Jack Zhang]

Part of the reason why X264 is faster is because it supports encoding multiple threads better while Compressor and Quicktime H.264 aren't optimized for multi-threaded rendering.