Converting 1080/50i --> 720/50p (and keeping slow-motion!)

[visual_artistry5D70]

Hi there,

How can I convert 1080/50i footage to 720/50p footage?

I had a shoot day over two days filming with a C300. The first day the camera shot at 720p (50fps) as we need slow-motion from both days. The second day the footage was shot at 1080i (50fps). Is there any way to cleanly convert the second day footage to match the first day, and therefore being able to interpret the footage at 25p for slow-motion?

Thanks!

[SAFEHARBOR11]

Your 1080i footage is NOT 50fps, it is only 25fps. The "50" refers to fields, each of which is only half a frame. So will not be able to equal the slow-mo quality if 50p with your 25p (from 50i source), sorry.

Thanks

Jeff

[visual_artistry5D70]

Ah, I was hoping sacrificing resolution (1080 -> 720) may have meant there was some way of going to 50p.

But as there's not, can I convert my 1080/50i footage to 1080/25p without quality loss?

[SAFEHARBOR11 · Accepted solution]

Your issue with your slow-mo is not video resolution, but rather is temporal - having to do with time. When shooting 50p, the camera captures a complete frame 50 times per second. When shooting 50i, the camera only captures frames 25 times per second (via 50 fields 50 times a second, but frames are what matters here). Thus you cannot expect the same smooth motion at 25p as you get with 50p, as you have only half the temporal resolution.

So what format do you really need to deliver at, the 720p25 or 1080p25? Either way, just drop the 1080i footage into the 720p or 1080p sequence and it should work out automatically.

Thanks

Jeff

[visual_artistry5D70]

Ah I see. That's very clear - thanks for the explanation!

Final delivery will be 720p25. If I do as you suggest, will that automatically deinterlace any jagged edges in motion, have the same motion blur as footage natively shot at 25p (considering all footage was shot with a shutter angle of 180 degrees) etc?

[SAFEHARBOR11]

Well, not really the same motion blur. With 1080i, each frame is made from two fields, however those two fields are grabbed at different moments in time, 1/50th of a second apart (that temporal thing again!) using 1/50 shutter. So when you combine those two fields (from different moments) into a single frame, anything moving like an arm waving or car driving by will have some "blur" on the moving parts of image as the two fields don't match up - subject is in different places in the two fields. With 25p footage, each frame is grabbed complete in the same moment, so will look a bit different than two fields from different moments combined look.

Image courtesy Wikipedia

Now, I've taken 1080i timelines and exported them as 1080p and looked good, I didn't need to do anything special. However, when dropping 1080i clips into 1080p or 720p sequence, see how it looks when played back in Premiere. If you can see the interlacing lines, then you'd need to right-click the clip and set to Deinterlace to remove those artifacts. Also, if putting 1080 clip into 720 sequence, then right-click clip and Scale to Frame so it fits the smaller frame.

Thanks

Jeff

[rodneyb56060189]

I'm not an engineer or pro broadcast person, but I felt compelled to say something for the fun of it.

In the days of broadcast TV ( the first foray into sending images over the air to the TV ) there were scientific challenges. Movies were already playing in theatres. ( Silent movies, etc. )

Camera ( Edison ) smart people figured out that 24 FPS worked good in movies because you basically show 24 frames per second and the human eye latency ( ability to see a fast image projected one after another ) made all the individual 'frames' ( basically still shots) imitate live motion ( the real world ) pretty good. This gave rise to the Mitchel movement of motion picture cameras.

In broadcast land, there were problems using radio waves ( basically an FM band I think ) to duplicate that. For one thing, TV's had an electron gun at back of cathode ray tube which was controlled by a magnetic field. The magnetic field made the electron gun ( this is CRT) move right and left and up and down really fast. It shot electrons to the front of the TV and illuminated the screen. In the US the electric grid is 60 cycles per second. In the UK the electric grid is NOT 60 cycles per second ( something to keep in mind re: NTSC and PAL ).

The radio waves going from broadcast antenna to antenna for TV didn't have the bandwidth (speed and data capacity ) to send a full frame at 24FPS. Also, it likes 30FPS better,  because if you send half frames on a 60 cycle electric grid, the little electron gun is vibrating and moving in such a way that it can do HALF FRAMES ( half of 60 cycles per second is 30 ). So the smart people made the INTERLACED half frame stuff, that COULD be broadcast over the air. The eye latency of human is OK with seeing half frames and blending them together in your brain when watching old TV stuff.

So, in the past, people would describe things as ( for example) 720i 30 FPS.  Now, that means the image is interlaced ( lower or upper field first etc. ). Which means that odd or even lines of the electron gun are being drawn first in one field and then the other half ) The two fields make a 'whole frame'.

Some camera manufacturers may be selling their stuff saying it shoots 720 at 30i, or 1080 at 50i. I have no clue. There seems to be some confusion now about frame rate and the resolution (product) is interlaced or progressive.  They are two different things. Frame rate should be frame rate. Resolution should be interlaced or progressive.

This complicates conversations about slow motion and all sorts of stuff, when the two things are confused with each other.

: )

[rodneyb56060189]

Following that basic train of thought, just for the heck of it.  Now, let's say you are shooting 720i at 50 FPS.  What is happening is that you are getting 2 half frames, completing a full frame, AT 50 FPS. So, you FPS speed is 50 FPS. It is capturing a composite of 2 half frames to make a full frame AT 50 FPS.  The SHUTTER ( based on 180) would be 1/100th of a second. Just like shooting 24 FPS is 1/48th of a second.

You can ( in todays world everything is going digital and all sorts of things are possible that you couldn't do with motion picture film cameras ) make your shutter speed something OTHER than 1/100th. And that's a different subject.

hehe, it's amazing how confused I am about what is going on today !

: )

[SAFEHARBOR11]

"Now, let's say you are shooting 720i at 50 FPS"

The extra input is appreciated, but we should take care to use correct terminology to not confuse readers. The second number is the one used to describe the format, in horizontal resolution.

PAL video (SD) is 720x576 lines, and would be called 576i, while NTSC is 720x480 lines and would be 480i. The "i" because PAL and NTSC TV broadcasts were interlaced, although it is possible now to create progressive 576p or 480p SD video for DVD or electronic delivery.

"720" is used to describe 720p HD video (1280x720 lines). Note that there is NO interlaced option for 1280x720 HD, it is always progressive, so 720p only and not "720i" ever.

1920x1080 HD video can be interlaced or progressive, thus the 1080i or 1080p notation. For NTSC areas, the 1080i frame rate is always 29.97, but for convenience/marketing/ whatever, you may see it called 1080i30, 1080i60, or 1080i59.94, but they all refer to the same thing! The 59.94 and 60 refer to the number of fields rather than frames, 60 just being rounded from 59.94 since 60 looks better in print. Even our beloved Adobe Premiere, for a new AVCHD sequence, will say 1080i30(60i). What the heck is that??!! Neither is correct...is all 29.97 frames/59.94 fields.

For PAL, might be called 1080i25 or 1080i50, but both the same thing at 25 frames/50 fields per second.

For 1080p, there are more frame rate options for NTSC land, being 24p (23.976fps), 30p (29.97), or 60p (59.94) with the latter really being 59.94 full frames per second, not to be confused with the 59.94 fields per second of 1080i.

1080p for PAL users can be 25p or 50p, even numbers, no fractions.

Where did NTSC-users get the fractional frame rate anyways? Early black and white broadcasts in the US did use 60fps to match the 60Hz electrical system, but then later they wanted to start broadcasting in color, while keeping the new color broadcast signal compatible with the older b/w TVs already out there so they would not be obsoleted. They figured out how to piggyback the color info onto the existing b/w signal, but to make it work they had to slightly alter the frame rate, and the rest is history, been stuck with that abomination ever since.

To add to the comments about fields - when the electron gun on the earliest CRT sets would "draw" the TV image one line at a time, top to bottom, by the time it finished drawing the last of the image at the bottom, the glowing phosphor dots in upper portion of the screen were already dimming, losing their glow, so that would cause the image to flicker as the next pass would start out bright again. So the engineers decided to split a frame of video into two fields (half-frames). One field was the even lines, the other the odd. Drawing a field would take half the time of drawing a full frame, so it could be completed quickly before top started to fade away. So the even lines were drawn in basically 1/60th of a second, then the odd in another 60th, resulting in drawing a complete frame in 1/30th of a second, but without the flicker.

If you Google this stuff, the pros can explain and illustrate far better than I, but hope this makes sense. With new LCD and LED displays, scanning lines to the screen is no longer an issue and interlaced ought to just go away since Progressive is much cleaner without the interlace artifacting (temporal changes between fields).

Back to the original issue at hand - just dropped a 1080i clip into 1080p30 sequence and see no interlacing issues. Premiere is I believe smart enough to say "Okay, I'm gonna combine the two fields into a frame first, and then display each frame in a progressive sequence one after another instead of showing a field at a time".

Thanks!

Jeff

[rodneyb56060189]

Thanks for info !

So, basically, the poster got hoodwinked into thinking he shot 50 FPS when in fact he shot 25 maybe ?

Re: interlaced vs Progressive, I'm OK, but about 3/4 of the world ( Africa, Asia, India, USA rural areas in Midwest, etc. ) don't have cable or dish and if they are LUCKY get some kind of broadcast ( doubtful ). So giving a broadcaster an interlaced product just makes it easier for them to broadcast it. Those with analog TV's or flatscreens, deal with it as they can, if they even GET a signal.

That's partly why cell repeater towers and sats are so popular. You can watch TV and movies on little cell phone ! How cool is THAT ?

Much cheaper for provider to get in contact with population via phone than laying down cable or fiber optic or whatever.

Providers get 'subscription' ( offset cost of providing) , like Netflix, and so on.  Watch stuff on 4" screen !  How cool !  Plus have internet !

World is changing fast re: media.

: )

[rodneyb56060189]

I did as you suggested, and googled stuff and I think my head is gonna explode soon.

[SAFEHARBOR11]

"World is changing fast re: media."

You are so right! Now, seems all the phone cameras and screen capture utilities are wanting to record using Variable Frame Rate, so wrap your head around that for a moment. Frame rate in recorded clip is all over the place, totally inconsistent from one moment to the next...

Thanks

Jeff

[James_eater]

Luckily most of us aren't relying on cameraphone footage to piece together our projects. Yes I do understand that it does happen time to time and that people are using Premiere and the like to put together vertical content for phones. Thankfully Handbrake is there to save people from the headache of variable frame rates.

[rodneyb56060189]

Meanwhile the poster is trying to figure out how to drag out his footage and tween extra frames or whatever, to make is slow motion !

Oh Noooo !

[James_eater]

I'm trying to figure out if it's even worth suggesting Twixtor

[rodneyb56060189]

I have no clue. I have noticed from people who shoot stuff and give me info, that around 120 FPS is when slow motion really starts to look pretty.

[rodneyb56060189]

http://www.tomwestondp.com/page/videos

first video top left, around 1:57 some slow motion...160 fps

sorry, I dont have stuff to capture and just post snippets, etc.

[rodneyb56060189]

whoops, meant like 120 fps

[rodneyb56060189]

I looked up c300 on internet. It came out a while ago which shows how behind the times I am. I personally would have found the 50i confusing, but we've been through that. It has really cool stuff on it. Gen lock, XLR for sound, SD (bnc) for output (probably like 2G SDI out ?), cool options for lens mounts, etc. Pretty nice.

: )

[SAFEHARBOR11]

"Meanwhile the poster is trying to figure out how to drag out his footage and tween extra frames or whatever, to make is slow motion !"

I apologize, we really got off on a tangent there!

With the speed change in Premiere, you will see options for Frame Blending and Optical Flow. The latter, I believe, creates or interpolates new frames to increase smoothness of slow-motion. Depending on content and speed, it can work pretty slick, but will not look identical to say 60p in a 30p sequence at 50%, where you are playing all original frames. But certainly something to try, may look better than duplicating frames from a 29.97i source

Thanks

Jeff

[Dean_Utian]

As Jeff mentioned - the 1080i is fields (odd and even) so is half full frames.

Here's a bit more to the explanation.

The 'i'  refers to interlace - and saves in fields.
'p' refers to progressive - saves full frame information.

Generally, it's better to record in progressive mode.

For more details on progressive vs interlace, see the article below:
https://photography.tutsplus.com/tutorials/choosing-progressive-versus-interlaced-video-recording--c...

[visual_artistry5D70]

Thanks for the help all! I ended up doing as you suggested SAFEHARBOR11​ which has worked a charm. It looks like PP is intelligent enough to realise I want the fields combined into a single frame - so essentially a 25p sequence with no interlacing artifacts.

Re the slow-motion - I am aware of Twixtor but I usually default to Optical Flow first. I've seen pretty decent results all the way down to 50% so will give that a go.

Got pretty detailed in this thread at one point but good to have the technical background. I feel like I'm now pretty well-versed should this issue ever come up in the future!