Video can be shot, edited and delivered in more shapes and sizes than ever before. In this short guide we’ll try to explain frame size, frame rates, interlacing and progressive scan in plain English.
What the numbers with letters at the end mean
You’ll see numbers like 720p or 1080i used to either describe a camera specification, a video file or an option when saving a video. The numbers relate to the height of the picture frame in pixels:
480 = 720 x 480 pixels and is normal for NTSC type standard definition (SD) video.
576 = 720 x 576 pixels and is normal for PAL type SD video.
720 = 1280 x 720 pixels and is a high definition (HD) format.
1080 = 1920 x 1080 pixels. This is also high definition and is usually described as Full HD.
2K, Digital Cinema, 4k and UltraHD bring a whole new combination of frame rates and sizes – we’ll stick with HD video resolutions for now.
The letter at the end tells you whether or not the video is progressive scan ( p ) or interlaced ( i ):
p = Progressive scan. This means the picture is recorded in full frames in one go.
i = Interlaced video. This means the pictures is recorded in alternate odd and even scan lines or “fields”.
Online content is always progressive scan. If you shoot interlaced then you will need to de-interlace the content at some point for online delivery. This is usually best left to the end of the edit at the rendering stage especially when the content is being sent to multiple destinations e.g. Blu-ray, DVD, broadcast and online.
Most standard SD video and many HD recordings including broadcast TV are interlaced. Using interlaced images has a couple of advantages. It reduces the amount of data needed to store or transmit the video. The alternate lines (fields) are recorded sequentially so with a moving subject each field shows a slightly different image. When interlaced video is viewed on screen the human eye doesn’t notice the image is based on fields and is fooled into blending them into full frames thus creating smoother looking motion at lower frame rates.
Old TVs with a tube (CRT screens) were all interlaced. Modern flat screen TV panels are progressive scan. You can play interlaced video on progressive scan TVs. There’s no need for the viewer to adjust anything because the TV can work out what to do with the image (de-interlacing). Computer graphics card adapters and displays are progressive. Interlaced footage viewed on computer displays can make the footage look jagged or coarse if the software cannot de-interlace the files correctly. If you are editing video for interlaced delivery then you should preview the footage on a proper video output with editing hardware such as a Matrox or BlackMagic card to ensure that what you see is what you are actually going to get.
Frames rates? What’s all that about?
The frame rate of a video describes how many times per second the video picture is updated. The higher that number, the smoother the motion in the video will appear to the human eye. Video with lower frame rates can, in some circumstances seem to flicker or judder especially during motion such as when the camera pans across a scene.
The reason we ended up with different frame rates in different parts of the world is because TV cameras, TVs and everything else in the broadcast chain were connected to the mains supply. Here in the UK the mains supply runs at 50Hz whereas in the other countries the mains runs at 60Hz. It therefore made sense to base the refresh rate of TV equipment around the frequency of the mains supply for any given country. In 60Hz countries they started out using 60Hz for TV but when colour pictures came along they slightly altered the refresh rate to to 59.94Hz for technical reasons. The odd number creates a bit of confusion – 59.94Hz is often rounded up to 60Hz. Half of 59.94 is 29.97 but is often rounded up to 30 for convenience.
These are some common frame rates or “frames per second” (abbreviated to fps) and where they usually apply:
24fps – this is the frame rate of film. In video it tends to be 23.976fps that’s used to mimic the “film look”.
25fps is 50Hz halved & used in SD or HD. Usually PAL countries like the UK, Australia and most of Europe.
29.97fps is 59.94Hz halved – Used in SD or HD. Usually NTSC countries incl. USA, Canada, Japan.
30fps – Some cameras do actually record 30fps but often it might really mean 29.97fps rounded-up.
50fps – Used for HD recordings in PAL countries – gives a really smooth motion pictures.
60fps (usually 59.94 rounded-up) – Used for HD recordings in NTSC countries – again gives smooth motion.
Joining the numbers, letters and numbers together
Now we know what the different bits mean we can hopefully understand the full thing easier. Here goes:
720p/50 = Frame size 1280 x 720, progressive scan with 50 frames per second.
1080p/25 = Frame size 1920 x 1080, progressive scan with 25 frames per second.
With a bit of luck that makes perfect sense. It would be great if things were this simple and when describing progressive scan video it pretty much is that easy.
We’ve already explained that interlaced video images contain alternate lines or fields. Each field contains half the information needed to draw a full picture. The numbers for frame rates should only describe full frames. So an interlaced video with 50 fields (or half frames) per second actually only has 25 full frames of information per second. Hence it’s written as 25.
1080i/25 – Frame size 1920 x 1080 Interlaced with 50 Fields Per Second.
480i/30 – Frame size 720 x 480 interlaced with 59.94 fields per second.
It’s worth noting that all 1280 x 720 video is progressive scan – there isn’t an interlaced version.
Forward slash frame rate
You may see video described as 50i. Most people would accept this is 50 interlaced fields per second but when it’s shown in context next to a frame size the EBU preference is to always describe the frame rate 1080i/25 and NOT the field rate.
So 1080i/25 does mean exactly the same thing as 1080i50 that you may see elsewhere. The forward slash in the middle indicates that it’s EBU preferred terminology.
Odd sizes and frame rates
Most video cameras and TVs show a landscape picture. The picture is wider than it is tall. But these days, especially with mobile phones video can be shot in portrait mode so the image is taller than it is wide. So when we shoot a full HD video portrait the picture might be 1080 wide x 1920 tall at 30 frames per second. It’s still a 1080p/30 video.
Some recordings, such as in HDV video camcorders, and many HD TV signals are stored or broadcast at 1440 x 1080i. This is another bit of trickery used to reduce the amount of data needed to record or broadcast the footage. The pixels in the video are oblong (non-square). The pixel aspect ratio is 1.33:1. Essentially this means the pixels are stretched horizontally to fill a 1920 x 1080 frame during playback. This is hardly noticeable to the average viewer. You may also see 960 x 720 pixel video from some cameras. Again these employ non-square pixels to generate a 720p image.
Sometimes cameras can run at low, variable or selectable frame rates. An example of this might be a low end web cam that might run at 15fps because that’s good enough for a talking head shot or to fit in with a slower internet connection. On a faster connection the frame rate might be increased to 30fps. Note: The camera itself possibly runs at 30fps all the time but for technical reasons it’s picture is only recorded or transmitted at lower frame rate.
It’s sometimes necessary to deliver progressive video with equipment that expects (or was designed for) interlaced video. This is achieved by using Progressive segmented frame or PsF. It’s similar to interlaced but the two fields are identical.
Very high or low frame rates are employed to produce a special effect such as ultra-smooth slow motion or time-lapse videos.
We hope you find this quick guide helpful and easy to understand. Feel free to ask a question or comment below. We’ll do our best to reply.
Thanks. It is very helpful
I need to do a recording with 1080i camera with 1920×1080 frame size with 25fps. Is it possible in 1080i?
which camera is useful?
Hi James,
1080i cameras record 50 fields per second. You can de-interlace the image to make 25p.
Nearly all modern video cameras (PAL UK models) can do 1080p. Some but not all will do 1080i as well. In essence the choice of camera depends largely on how much you want to spend and what type of activity you want to film.
Video cameras with smaller image sensors are better when there’s a lot of action, moving around, longer duration events etc. Large sensor (DSLR type) cameras are more suited to relatively static subjects and will give a different ‘look’ than a video camera. This isn’t a fixed rule – some DSLR cameras now have fast AF and servo zooms that rival traditional video cameras. Likewise there are now video cameras with larger sensors that give you some of the benefits of both. Most large sensor cameras don’t do 1080i (usually 25p or in some cases 50p).
Interesting, Gavin. Thanks for that. So when you guys go out to shoot on location, say, at an office or factory, what frame rate do you mostly shoot at? I’ve shot at 1080i for years but never really knew why!
That’s a very fair question Martyn. 1080i was and can still be a great shooting option for some cameras. The interlacing achieves smooth motion at a low 25fps (50 fields). A lot of cameras such as the EX1/3 and PMW350 could only achieve either 50i or 25p at 1080. For fast action such as sports or a live event 25p could produce stuttering with horizontal movement so 1080i or 720p50 was preferable. For most web based jobs to date we have used 1080p25 or 720p50 but our latest cameras are capable of 1080p50 so that’s what we use now. The online world is also offering higher frame rates with YouTube starting to show content at 1080p50 and 1080p60 in the last couple of months.
Hi. This all makes so much more sense. Thank you very much.
I was just wondering about file size…
If I shot 1 min video at 1080/25 and then exactly the same scene again for 1 min at 1080/50 would the 50 frames file be twice the size?
What I mean is 25frames be 200mb and 50frames file be 400mb? Or does it not work like that?
Hi Dean,
Thank you for your question. The file size is dependent on the data rate of the file rather than the frame rate.
When recording in camera you will have access to different data rates in megabits per second (Mbs). Sometimes described as a quality setting such as SP or HQ. The flexibility to select a specific frame rate or data rate combination varies from camera to camera.
Common bitrate options on professional cameras include 35Mbs, 50Mbs and 100Mbs. However, not all frame rates can be recorded at all of those data rates. e.g. 35Mbs works with 1080p25 but 35Mbs may not be an available option for 1080p50.
In theory 1080p50 at 100Mbs would produce double the file size of the same content at 1080p25 50mbs if your camera allowed those options.
Does that help?
Hey!
recently i downloaded a few videos from internet. few were having frame rate of 25 fps while some were at 29 fps.
Howcome 29 fps? is it a standard for internet videos?
29.97 is used in USA/Japan. Many webcams and most mobile phones globally default to 29.97 or 30.00.
That’s primarily the reason why 29.97 is so widely seen online.
Hi,
Novice here.
I’m wanting to use quicklime to shoot 720p/30 on my mac, and my two iPhone’s as cameras, also 720p/30. But my Zoom HQ8 camera only shoots 720/25 @ 8MBS 0r 720/50@ 16MBPS (that is when its switched to Pal. Im in Austrasoia)
When I switch it to NTSC it records 720/60 @15mpbs, or 720/30 @8mbps
However when i look at the specs on the footage from my Zoom, Final Cut says it is 720/29.97. Is this close enough to edit? Or is it a problem to edit NTSC with iPhone video?
Hi Mary,
I’m not familiar with the Zoom HQ8 camera BUT it’s likely that it is shooting 720p60 (that could actually be 59.94 interlaced or progressive).
Final Cut is usually fine with various fame rates – especially from NTSC sources.
Often kit spec says 30fps but it’s really 29.97fps or vice-versa. Again FCPX will happily edit the lot on the same timeline with no ill effects.
One thing you need to watch is that your project settings (timeline) must have a frame rate of 29.97 or 30fps.
The default in FCPX is to set project to match first piece of content. You can over-ride this and enter the settings you want.
iPhone footage is often variable frame rate – it might be identified as 29.97 or 30 but it may not be constant. Depending on the camera (front/rear), the device model and portrait/landscape filming mode some units record at either 24fps OR 30fps. Both are compatible with NTSC 29.97 insofar as FCPX is concerned.
I’m confident you won’t have any problems but to test that I recommend making a short, simple edit from all your sources and export that to a file. See how the edited file looks.
iphone 6 movies are not the format or size suitable for video editing (PPro cs4 adobe encoder does not work) can I purchase file converters to avi or other suitable formats at 4/3 ratio, is this possible? Are you able to recommend?
David
Hi David,
iPhone 4 records 16:9 aspect ratio 1280x720p video via the main camera at a nominal 30 frames per second. However, Apple devices tend to record at an irregular frame rate which causes Adobe Premiere to choke on the files.
The quickest fix for making iPhone videos compatible with Adobe Premiere is to run the file through Handbrake Website.
Choose one of the 720p30 presets (or the iPhone/iPod preset). This will convert the .mov from the iPhone into an MP4. The MP4 file should work fine inside Premiere.
If you’re using the front facing camera then it will be 4:3 aspect ratio 640x480p up to 30fps – again the frame rate will be variable. You can run these through Handbrake too.
We’ve found Handbrake to be very useful. It’s completely free and safe in our experience.
Gavin
Working on a project using 16,5 mm 16mm 8mm and S8mm that has been transferred to digital.
Some of the 8mm was transferred interlaced. This is causing a banding artifact when viewed in hi res full screen.
Is the a way of undoing the interlaced so we wont get the banding artifact? We had up sized it all to 1.5 to match better with the 16.9 but the upsizing makes it much worse. Beside gong back to 1:33 ids there anything that will help get rid of the banding artifact? Thanks Rich Allen filmmaker Rhode Island US
Hi Rick,
Thanks for your question. Film scanning is outside our direct experience hence this isn’t going to be a definitive answer. If you still have the 8mm files as they were before being upscaled then there may be a chance to de-interlace those. My thoughts are that you may have to get the 8mm re-digitised progressive scan to get clean files.
Gavin
Please reply asap.
If I burn 29.97fps video to Freemake Video Converter, dvd, which is ALWAYS set to 25fps, my video reproduces jerky.
I can change Frame Rates using Xmedia Recode Video Converter. The choices are: 23.976; 24; 25; 29.97; 30; 50; 59.94 and 60 FPS.
If I was to convert 29.97fps to 59.94fps, would the outcome, burned to 25fps dvd be steadier on the eye, please?
I need to know this urgently, so please write very soon.
Regards.
Hi Paul,
Thank you for your comment.
Frame rate conversion is hard to do well.
You should be able to burn 29.97 content as a 29.97fps DVD. Avoiding frame rate conversion is the best policy.
I’m not familiar with the software you mentioned. However, I am confident that you’d be wasting your time converting up to 59.94 then down to 25fps.
See if Freemake can be set to 25fps. If not look at another authoring and burning solution like AVS2DVD would be my advice.
Gavin
Thank you for writing.
Freemake Video Converter is fixed on 25fps.
Your article seemed to imply that “the bigger the number, the smoother the picture will look on the eye”. Therefore I thought converting 29.97 over to 59.94, (a bigger number), would be the solution?
29.97fps is a very bad Frame Count. I wish it did not exist, because I always seem to wind up with it with films. 23.98 is a fraction but this one works out smooth on the eye. 29.97 always looks jerky or choppy as some call it.
Hi Paul,
The thing about standard definition video and smoothness is that it was done using a trick.
Nearly all standard definition video originated as Interlaced rather than Progressive scan.
PAL standard def video is 50 FIELDS per second (not FRAMES).
NTSC standard def video is 59.94 FIELDS per second (not FRAMES)
Video was split into two FIELDS to create smoother motion using analogue technology within the bandwidth available.
This video explains it a bit https://www.youtube.com/watch?v=rCUjvK-zbHw
If you convert a source video from 29.97 FRAMES PER SECOND video to 59.94 FRAMES PER SECOND all you will do is duplicate each frame. You won’t be creating new frames with any additional motion. AND because you’re encoding to DVD it’ll either need to be rendered back to 29.97p or (more appropriately) 59.94i.
I started out in my last post explaining that frame rate conversion is hard to do well. That process can become more complicated if you also need to change the footage from progressive to interlaced (which is preferable for most DVD material).
I’m not familiar with the software you use BUT what I can tell you is that when we convert video between standards we either do it from analogue tape with a $2,000 Teranex unit or with files we make to very deliberate encoding choices in software by manually overriding the software defaults to force Adobe Media Encoder to deliver exactly what we want (which we know from experience works).
Gavin
Thank you again for writing.
Hi, Hope you don’t mind me writing again, but I have discovered that Freemake Video Converter, burn to DVD, can be switched from 25fps Pal to 30fps NTSC. Region Zero.
I am wondering if I should select NTSC when I burn the dreaded 29.97fps videos – then the picture playback might not be jerky or choppy like it is on 25fps Pal(?)
Would 23.98; 24; 25 Frames Per Second also reproduce smoothly burned to NTSC, do you know? (I sometimes put several videos onto the same disk and they are each of different frame counts.)
I think I am correct in saying Region Zero will play on any dvd player anywhere in the world(?)
Can you advise me on these points please?
DVDs need to be either PAL or NTSC type. You can’t mix frame rates on the same disc so yes – settle on a standard (NTSC in your case).
If you covert from 25fps to 29.97fps in the most basic conversion some frames will simply be duplicated. Better software will blend the frames to provide a smoother conversion. You need to see how well your software performs. Give it a go.
29.97 is a standard frame rate for many HD video files. Whilst you can use progressive scan footage to make a DVD (most films were shot 24p encoded at 23.98p). NTSC Standard Definition was based on 59.94 interlaced fields per second. Even if the source is 29.97p. your encoding software should sort out that aspect of things when it renders the MPEG 2 file ready for authoring.
All recordable discs are Region Zero. There is no region code possible. Thus they will be universally playable in global DVD players.
Thank you. I will try it.
Hi, I did as you suggested: I burned a 23.98; 24; 29.97 frames per second videos to 29.97 NTSC, (not 25fps Pal), and the result is rock steady pictures!
The only one I could not test at this time is 25fps.
Any theories? Do you think 25fps converted to 29.97fps NTSC will also look steady? (The Freemake Video Converter is always Region Zero.)
25fps is the correct frame rate for PAL and should look smooth with a PAL type DVD.
You can try making it at 29.97fps and see how it looks but the base frame rate is PAL type.
como posso medir distancias entre objetos existentes numa frame
A fotogrametria é uma tarefa complicada. Se você tiver acesso à mesma câmera, lente e local, poderá reconstruir a cena e fazer medições.
Esse é o método simples. Calcular distâncias sem reconstrução pode ser muito difícil. É uma área de especialização que não temos.
Gavin
Fancisco’s question in Portuguese asked about measuring distances between objects in a frame.
I answered that photogrammetry is a difficult subject and that a reconstruction would be the only simple way to do it. It’s not our area of expertise.