How do I shrink the size of my phone videos?

Guardian Technology 05 Mar 2020 08:00
Shooting video and photos takes up a lot of space, so what’s the best way to save storage? Photograph: Samuel Gibbs/The Guardian

How can I compress videos so I don’t lose a lot of the quality? My phone, a Samsung Galaxy S10, makes really high quality videos but I would be satisfied if they looked like normal videos. Yanis

Videos take up a lot of space, and a lot of research goes into making them smaller. Other things being equal, a key factor is the size of the image, just as it is with still photographs. You can also reduce the file size by arbitrarily reducing the data rate or, for preference, by using a more efficient video compression system. The current favourite is MPEG-4/H.264/AVC (Advanced Video Coding), which is usually called MP4 for short. Technically, MP4 is the file container while H.264 is the codec that codes and decodes the video.

There are some good reasons for reducing video file sizes. For example, you might want to customise a high-resolution video for a low-resolution screen. You might also want to fit several videos on a device with limited storage, such as a smartphone or tablet, or an optical disc such as a CD-Rom or DVD. You might want to send the video to someone else; reducing the file size will reduce the upload and download times.

A standard computer screen with a resolution of 1280 x 1024 shows 1,310,720 pixels, which is 1.25MB. Your Samsung Galaxy S10 can shoot videos at an even higher resolution of 3840 x 2160 pixels or UHD (ultra-high definition), where a full screen image needs 8,294,400 pixels or 7.9MB – more than six times as much. Even with compression, 30 frames per second adds up.

When reducing video resolutions, it is very important to keep the same aspect ratio (width to height). If you don’t, clocks will no longer look round and faces will be distorted so they are either squashed or elongated like a Modigliani portrait.

When you reduce the resolution of a video, it fills a smaller area, so you don’t need to send the screen as much data. However, in some video editors, you can set the data rate to almost anything you like. This will reduce the image quality as well as the file size.

One of the best ways to reduce the size of a file is to change the way it’s compressed. Today’s leading codecs, mainly H.264, are much more efficient than the ones typically used in old mpg, wmv (Windows Media Video) and avi files. Video transcoding programs usually take it for granted that you’ll want to convert any old video into some form of MP4/H.264/AVC.

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