Today’s cameras have become increasingly more capable of producing excellent video files, with this comes some confusion for those of us who have used the camera primarily to make photographs. Although there is a lot more to understand than is covered in this article, the text below written by Rob Will has made a great start.
Sensor Resolution
Sensor resolution is what we see when we buy a camera for example the A7rIV is 61 MPx (9504 x 6336), the XT4 is 26 MPx (6277 x 4157), and the a6600 is 24 MPx (6000 x 4000).
Video Resolution.
Video resolution is based solely on the number of horizontal pixels on the sensor. The number of vertical pixels used depends on the aspect ratio. The most common cinematic aspect ratio is 16 x 9. Assuming that the camera uses the entire sensor width for video (they don’t always), the 16 relates to the camera’s actual sensor width in pixels, and the 9 is mathematically derived based on that. What that usually means is that the top and bottom of the image are thrown away so as to give the widescreen aspect ratio. A 4K resolution means that the width used for video is 4096 pixels; 6K resolution is 5568 pixels wide and 8K is 7680 pixels wide.
Some cameras have many more pixels than that. The Sony A7rIV for example is 9504 pixels wide, but that doesn’t mean that it shoots 10K video. The camera’s processor oversamples the sensor and produces a 4K video image. The XT4 does the same thing downsampling to 4K from its 6277-pixel sensor.
Frame Rate
Frame rate is the number of times per second that the camera’s processor can read all the pixels and do the appropriate downsampling. A typical movie from the film days was recorded at about 24 FPS. This is because the projectors were all timed to that speed, and it was “fast enough” to give decent quality. Faster is better to a point. 30 fps or 60 fps produces less flickery video. Monitors these days (unlike film projectors) aren’t created with a single “natural” speed, so 24 up to about 60 fps is considered good for video these days. There is no point in going faster because our eyes can’t detect the difference. When you see speeds like 120 fps, this is almost always used for “slow-motion” video.
The biggest determining factor on frame rate is processor speed. The XT4 can do 60 fps because it is sampling far fewer pixels for every frame due to its lower resolution. This is where the layered sensors with their blinding fast read speed can really help – especially on higher resolution sensors.
| Frames per Second | Description from Final Cut Pro | |
| 24fps | Film; High Definition Video | This is the universally accepted film frame rate. Movie theatres almost always use this frame rate. Many high-definition formats can record and playback video at this rate, though 23.98 is usually chosen instead (see below). |
| 23.98 (23.976) FPS | Film; High definition video with NTSC Compatibility | This is 24 FPS slowed down by 99.9% (1000/1001) to easily transfer film to NTSC video. Many HD formats (some SD formats) can record at this speed and is usually preferred over true 24 FPS because of NTSC compatibility. |
| 25 FPS | PAL; HD video | The European video standard. The film is sometimes shot at 25 FPS when destined for editing or distribution on PAL video. |
| 29.97 FPS | HD video, early black and white NTSC video | Some HD video cameras can record at 30 FPS, as opposed to 29.97 FPS. Before colour was added to NTSC video signals, the frame rate was truly 30 FPS. However, this format is almost never used today.* |
| 50 FPS | HD video, early black and white NTSC video | Some HD video cameras can record at 30 FPS, as opposed to 29.97 FPS. Before colour was added to NTSC video signals, the frame rate was truly 30 FPS. However, this format is almost never used today.* |
| 50 FPS | HD video, early black and white NTSC video | Some HD video cameras can record at 30 FPS, as opposed to 29.97 FPS. Before colour was added to NTSC video signals, the frame rate was truly 30 FPS. However, this format is almost never used today.* |
| 59.94 FPS | HD video with NTSC compatibility | HD cameras can record at this frame rate, which is compatible with NTSC video. It is also the interlaced field rate of the NTSC video. This number is sometimes referred to like 60 FPS but it is best to use 59.94 unless you really mean 60 FPS. |
| 60 FPS | HD video | High definition equipment can often play and record at this frame rate but 59.94 FPS is much more common because of NTSC compatibility. |
So what are the takeaways?
1. Higher sensor resolutions can theoretically produce better video because they can oversample more pixels, but they require much greater processing speed.
2. Faster processors and layered sensors can significantly increase the processing rate and should be able to sustain much higher frame rates with increased quality.
3. There is a lot of confusion in the market about the difference between sensor resolution and video resolution, and manufacturers count on that and confuse us with bullshit. Example: Don’t assume that a very large desktop monitor has very high resolution. I see 32″ monitors all the time that look great but are scarcely 2K when you look at the actual horizontal pixels. (Note: never buy a monitor with less than 4096 pixels horizontally).