Understanding output size

Daniel GibbsTechnical Articles

One of the popular more topics asked about by customers is the output size of recordings, with questions like “Why is my recording not the size I expect it to be?”, “Why is my recording blurry?”, “Why are there black bars in my recording?”, and “What does ‘use retina resolution’ mean?” This post aims to give an easy-to-understand explanation on output sizes, and answer all those questions and more. We’re going to be using iShowU Instant as an example, but the principles apply to our other apps as well.

Quick summary: To get the clearest recording, make sure your output size is set to the same as your input size. If you need a specific output size, read on to find out how to avoid scaling and letterboxing.

Input size

Before we get started on the output size, let’s take a quick look at the input size, the size of the area that’s actually being recorded. In iShowU Instant this is pretty simple; you select an area on the screen and that is the area that is recorded. If you select the full screen on a 1920 x 1080 screen, then the input size will be 1920 x 1080. If you select an area like 500 x 500, then the input size will be 500 x 500. The Summary section in Basic Mode and the Video tab of Advanced Mode shows you what your input size is.

Input size is important because it can determine what your output size is; if you change your input size, your output size might change too!

Selected area summary in iShowU Instant

Output size

Output size is the actual dimensions of the video file produced after you’ve finished recording. You can check the size of an existing video by opening it in QuickTime Player and pressing ⌘I. As you can see in the screenshot below in the Format section, it shows a size of 500 x 500.

Inspector in QuickTime Player

If you’re using iShowU Instant in Basic Mode and you haven’t changed any Advanced settings, then the output size will be the same as your input size; it’s as simple as that. If you record a 1920 x 1080 full screen, your output size will be 1920 x 1080. If you record a 500 x 500 area, your output size will be 500 x 500.

For a lot of people, this default behaviour is fine, but if you want to have a different output size than your input size, switch to Advanced Mode, and head on over to the Output tab and look at the options in the Video Size dropdown menu.

Relative sizes

The first group of options available in the Video Size dropdown are relative sizes; that is, they are relative to your input size. For example, if you select ½ input size then both the width and the height of your video file will be ½ of the input width and height (250 x 250). Note that iShowU Instant shows you the actual output size next to the Video Size dropdown menu.Relative output sizes in iShowU Instant

 

The table below shows what the output size will be for a 1920 x 1080 recording and a 500 x 500 recording for each of the relative size options.

Input size Same as input ¾ input size ⅔ input size ½ input size ⅓ input size ¼ input size
1920 x 1080 1920 x 1080 1440 x 810 1279 x 719 960 x 540 639 x 359 420 x 720
500 x 500 500 x 500 375 x 375 333 x 333 250 x 250 166 x 166 125 x 125

Absolute sizes

The second group of options available are absolute sizes; these sizes are not relative to your input size and will always be exactly the same no matter what your input size is. The sizes available here (4K, 1080p, 720p, 540p, and 480p) are all common video sizes in use globally. Because these sizes aren’t relative to your input size, there are a couple of things that may happen to your recording when you use these output sizes: scaling and letterboxing.

Absolute output sizes in iShowU Instant

Scaling

If your input size is smaller than your output size, then the recording will be scaled up to fit the output size, which can result in the recording looking pixelated or lower quality as you can see in the below image of part of a 960 x 540 recording using a 1920 x 1080 output size (the original recording being scaled up to 2 x its original size).

Comparison of scaled recording to normal recording

Letterboxing

If the aspect ratio of your input size is different to that of the output size, then either vertical or horizontal letterboxing will occur. This is when black bars are added to the sides (or top and bottom) to create the desired output size without stretching the recording. Below is an example of letterboxing where a 1080 x 1080 recording used a 1920 x 1080 output size.


A letterboxed recording

Absolute sizes summary

The table below shows what the output size will be and if scaling and/or letterboxing will occur for various different input sizes and each of the relative size options.

Input size 4K 1080p 720p 540p 480p
5120 x 2880 3840 x 2160 1920 x 1080 1280 x 720 960 x 540 640 x 480
1920 x 1080 3840 x 2160
Scaling up
1920 x 1080 1280 x 720 960 x 540 640 x 480
1080 x 1080 3840 x 2160
Scaling up
Letterboxing
1920 x 1080
Letterboxing
1280 x 720
Letterboxing
960 x 540
Letterboxing
640 x 480
Letterboxing
640 x 480 3840 x 2160
Scaling up
1920 x 1080
Scaling up
1280 x 720
Scaling up
960 x 540
Scaling up
640 x 480
400 x 400 3840 x 2160
Scaling up
Letterboxing

1920 x 1080
Scaling up
Letterboxing
1280 x 720
Scaling up
Letterboxing
960 x 540
Scaling up
Letterboxing
640 x 480
Scaling up
Letterboxing

What about retina?

Those of you with retina screens may have noticed the Use retina resolution checkbox underneath the Video Size dropdown menu. If you’re recording from a retina screen, you can tick this checkbox to record full retina resolution which will essentially double your input size, and therefore double your output size if you are using any of the relative output size options. This only affects the relative output size options; absolute output size options will still produce the same size videos. If you’re recording a high-resolution retina display such as a 5k display, check out this blog post.

Summary

  • By default, the output size will be the same as the input size. If in doubt, leave the settings like this.
  • If you want to scale down your recording and maintain the same aspect ratio, use one of the relative output sizes (¾, ⅔, ½, ⅓, ¼).
  • If you want to fit your recording to a fixed size, use one of the absolute output sizes (4K, 1080p, 720p, 540p, 480p) but be aware that scaling and/or letterboxing may occur.