iPhone Video Recording

10 Feb 2020 20:05:35

Rick Churchill

Reconciling iPhone video recording format with UK TV playback

I normally use a camera recording video at 1080p @ 25fps (frames per second) but during my last holiday I used my iPhone 11 which records @ 1080p @ 30fps (60 or 24 fps is also possible but no UK setting)

As a result when transcoded in Final Cut Pro to produce an mp4 movie @ 25fps there is an obvious jerkiness to panning which is a symptom of dropped frames. It is more apparent when the computer is connected to the TV screen.

If the movie is made at 30fps then there is no dropped frames apparent on the computer but there is still on the TV as it's screen is refreshed in sync with our 50Hz mains frequency.

Does anyone know of a way of showing movies on the TV made from the iPhone without this problem?

I wonder how this is prevented when streaming video, perhaps the source detects that subscriber is in the UK and sends the movie at 25fps?

Re: iPhone Video Recording

10 Feb 2020 23:10:59

Tony Still

Final Cut provides options for dealing with mixed frame rates in a single movie. If you're seeing dropped frames then you may be using a crude algorithm (perhaps 'nearest neighbour'). You could try other 'Frame Sampling' options, notably 'Frame Blending'; expect this to require more rendering/export time.

Disclaimer: I don't use Final Cut (I did read this).

Re: iPhone Video Recording

11 Feb 2020 11:53:11

Rick Churchill

Thanks Tony
I followed your link and was full of hope since it says "You can modify the project’s settings at any time" but FCP will not let me modify the frame rate while it has clips in the timeline. A Q&A here says cut them, change the rate and paste back in but mine are so complicated, linked with sound and titling I think that is impossible.

I may try experimenting with individual clips using the Frame Sampling option as you suggest to see if I can get an error-free pan to work on both computer and TV.

Re: iPhone Video Recording

11 Feb 2020 22:02:46

Rick Churchill

I will attempt to condense the last 8 hours into a few paragraphs! I followed the suggested way of changing the frame rate of an existing FCP project. DON’T DO THIS.

First the project is duplicated for safety. Secondly all the clips are selected (Cmd-A) and cut (Cmd-X). The project parameters are changed by opening the settings pane (Cmd-J) and “modify” is clicked. The frame rate is now available to alter as the project is empty. Afterwards the clips are pasted into the timeline again (Cmd-V). Surprisingly this part is much easier than I thought it would be.

Up till now you have a project of one frame rate which includes clips of different rate so you use the frame sampling option that Tony found. All the clips are selected and the Video Inspector opened. Scrolling down to Frame Sampling this is altered to Optical Flow which Apple advise is best for curing stuttering when frame rates are altered.

Then make a cup of tea, in fact make lots of cups of tea and a stiff whisky while you’re about it! Unfortunately there is a bug with the Optical Flow algorithm which I learnt about on the internet too late, which means whenever you think the Transcoding and Analysis has ceased and you want to create an export file (“Sharing” as Apple now put it) FCP advises that it is still carrying out background tasks and starts transcoding again. If you ignore this, which you have to in the end, you are rendered an unwatchable movie which stutters like a Southern Railway locomotive leaving Salisbury station. (Sorry trainsporting childhood creeping in there)

What is worse every time you open the project and attempt to “share”, FCP advises that it has background tasks to finish – transcoding Optical Flow.
I will try altering the Frame Sampling to another algorithm to see whether this clears the fault and provides me with a stutter free video but I need a days rest and more whisky!

Re: iPhone Video Recording

11 Feb 2020 22:44:05

Tony Still

You won't be following my suggestions again then...

Re: iPhone Video Recording

12 Feb 2020 15:16:29

Rick Churchill

Aaaaaaaaaaaaaaaaaaaaaah! Instead of playing the 30fps video via wi-fi and Apple TV to my TV, I connected an HDMI cable direct (my laptop is rather old-fashioned as it actually has several different sockets!) The output was smooth just like the laptop screen so it was the method of delivery to the TV that was causing the problem.

In future if I use the iPhone for s a movie camera I shall use 30fps as the video editor project parameter. With iMovie or Final Cut Pro it is the first clip that determines the format although in FCP it can be changed later. Just be sure to use an iPhone clip as the first even though you introduce still pictures or other clips in front.

Incidentally before my superstitions were aroused by the lack of others advising on the internet that they had similar problems I experimented late last night with using the "Frame Blending" rather than "Optical Flow" algorithm in the Frame Sampling to transcode from 30fps to 25 fps. The transcoding took very little time but the result gave a sort of double-image fringing in fast panning and motion. Not good for skiing shots.

Tony your suggestions are always welcome.