6.3 Video Editing

Unlike film, television (even digital television) typically uses a technique called ‘interlace‘: the odd-numbered rows of an image get sent first, and then the even-numbered rows (it’s a process derived from how cathode ray tubes scanned the image, back when television used cathode ray tubes, but that’s not important right now). Take this chess-board for instance:

If you see an ‘interlace’ setting, that’s what it does: It fillets your frames to half their size and interweaves them. This is great if your image is still but can be messy if things are moving about. If you ever work with television footage you’ll have to worry about something called deinterlacing which can prove to be a bit of a nightmare.

PAL television (the standard in the UK) uses 25fps (25Hz) but those 25 frames are interlaced meaning that you actually get an (albeit half-resolution) image 50 times per second: what’s referred to as 50i (where the “i” stands for “interlaced”). NTSC television (the American standard) works the same but at 30/50 fps: 60i. That’s why 30p is the predominant framerate for digital video.

Not every frame of a digital video is necessarily a full image in its own right. The vast majority of digital video formats utilise something called Group of Pictures (GOP) – sometimes referred to as key frame distance. At its simplest, this works rather like JPEG compression, but in a third dimension: one frame of video (a “key frame” or “I-frame”) is an actual image, and the next few frames are rendered from that reference image using maths. The larger the GOP, the greater the risk of distortion artifacts. This is why flocks of birds tend to look rubbish on digital television, and why it takes a while for the picture to appear when you change channels (the television needs to wait for the next I-frame before it can show anything). A GOP that’s twice the framerate (in other words, one I-frame every two seconds) tends to be standard. So if your framerate is 30fps, you’d want a key frame every 60 frames. But that’s just a guide, and if the content of your frame doesn’t change that much, you can afford a much longer gap.

It’s complicated, and tied up with ratios… 4:3 (four units wide by three units tall) is the old television ratio but has now largely fallen out of use, having been replaced by 16:9 which is the standard widescreen TV ratio. 16:9 is also the most common ratio for a computer monitor, as well as being the ratio favoured by YouTube.

But those are just the two most common ratios, and the history of film is littered with others. The width of a 4:3 video should be 1.33…× its height, while for 16:9 it should be 1.77…× its height:

Standard definition (SD) television has a height of 576 pixels in Europe (PAL) or 480 pixels in America (NTSC). The number of pixels making up the width is not the same as the number of pixels you see on your screen: on Freeview (the UK’s main SD TV platform) it can be anything from 544px to 720px which then gets stretched to 768px for 4:3 and 1024px for 16:9 (widescreen).

High definition (HD) TV comes in two flavours: 720px height, or 1080px height (sometimes called FHD). Widths of 960 and 1440 have been common for 1080 broadcasts, though a full-width 1920px is increasingly seen as standard.

Then there’s Ultra High Definition (UHD), also known as 4K (confusingly a reference to its width!). 4K is 2160px high (twice that of HD). It’s 3840px wide (a natural 16:9), or 4096px wide in cinemas (hence the 4K). Videos of this size require a lot of processing so can be difficult to run on older devices. But a modern phone may well be able to record at that scale, so pay attention to your settings.

To edit together a video, you need ‘assets‘ — the media files you will be using in your video. Your assets might just consist of a single video file you’ve recorded. But you could also import multiple video files, audio files or image files. It’s generally a good ideal to store all of your assets in a single folder and to give them sensible names.

If your assets are in common filetypes you should be able to import them into a video editing tool. There’s usually a section for assets somewhere to the left of the screen. Be sure to check that any images and video are of an appropriate resolution for the video you’re wanting to create (about the same as your frame size or bigger).

Once you’ve imported your assets you can drag them onto the timeline to add them to the video you’re creating.

The timeline is the main part of your workspace: it’s where you compile and arrange the various parts of your video.

You can add an asset to your timeline by just dragging it into place. Often added items will ‘jump’ to the end of the timeline, but you can then reposition them to start at a specific timecode along your timeline. An item on a timeline is generally known as a clip. How fine you can position a clip will depend upon your framerate, so typically it will be to something like a 25th or a 30th of a second. Clips may ‘snap’ to other clips, but you can generally control this behaviour in the settings or perhaps avoid it by zooming further into your timeline.

Tracks

The timeline consists of multiple tracks which follow a layer principle whereby video (and image) items on tracks at the top of the timeline will cover up items on tracks lower down — you can have multiple tracks running at the same time, but only one of them can be visible on the screen.

You can add more than one item to the same track, but be careful of overlapping them in the same track — it might cause strange things to happen.

If you add an image to the timeline it will be converted into a video clip with default play length (sometimes ten seconds) which you can then modify (usually from a right-click context menu or by dragging the right-hand edge of the clip to the duration you want).

Audio may be separated from a video file and run as its own track. This can give you a bit more control over the sound of your video. Audio tracks can often be edited using the sort of techniques we looked at in the audio section, and a lot of the conventions of multitrack editing apply here too.

Just as with cutting and pasting in text, the language we use around video editing dates back to analogue days when film would literally be trimmed or clipped (with scissors) to a certain length (measured in feet, hence footage).

Just as with analogue film, the digital clips you add to your timeline might be too long, or they might need cutting into pieces and rearranging. Typically you’ll want to trim the start and end to remove unnecessary footage. To trim, you usually hover over one end of the clip until your cursor changes, then click and drag the cursor inwards to remove the start or end.

To split a clip, you typically need to use the playhead — the marker on the timeline that shows the current point that is being played. Move this to the point you want to split the clip (using the video preview to help you know where you’re at in the video), then there should be a scissors icon or ‘Split’ button you can use to split the clip at that point. You can then move around the separated clips (including onto separate tracks) or delete unnecessary parts.

A transition is a visual effect that joins together two clips — for example a dissolve or a wipe.

A dissolve transition mixes between two clips.

You may want to add transitions between different clips, or between images and clips. You can even add special effects over a clip. Most video editors will have a selection of built-in transitions and effects, but you’ll probably want to use these sparingly unless you’re wanting something that looks like a cheap 1980s pop video — you don’t want to distract from your message and content.

To use a transition or effect, drag it onto the timeline over the relevant clip. You can then usually modify the properties of that effect to suit exactly what it is you want it to do.

You could import an image or video with text on it, but most video editors also have built-in options for adding text. Text can be added over clips or over a blank background, for example for credits (and if you’ve used any third-party materials then you’ll probably want to provide some credits). Locate the text options in your tool then drag onto the timeline. You may edit the text in the video preview pane or when you insert it. You might need to use different tracks to get the text to appear exactly as you want, such as an overlay.

Be careful about how much text you add, and make sure you use an appropriately sized font so your audience can read it.

Once you’ve edited your video together, it will need to be exported from the video editing tool into a single video file. There will be an Export (or Share) option, probably in the File menu or as its own button. You’ll be faced with a number of settings determining the kind of file you want to export, as well as its name and where you want to save it to.

Many video editors will give guidance around what each format is best for what use, and there may be some ready-made profiles you can use. For general use, MPEG-4 / H.264 / .mp4 are typically what you might want for a video you want to share or upload to a website. There will also be different quality options, and these will affect file size: higher quality videos can be very large files, so you might need to compromise quality in order to have a video that isn’t taking up obscene amounts of disc space, especially if you need to upload it to the internet. Take a look at our technical advice at the top of the page for a look at the various settings you’re likely to encounter.

Once you’ve chosen your format, there’ll be a button to select to start your export. It may take quite a while, depending on your video length and the encoding quality — the software will have to go through your entire video to create the file, so exporting might even take as long as if you were playing back your video from beginning to end; it may even take a lot longer!

Take a look at your exported video when it’s finished exporting. You might find that you need to try some different export options. I’ll put the kettle on, shall I?

If you’re wanting to share your video on the internet in some way, you’re going to have to upload it. As we’ve said a few times now, videos are usually pretty big files, so uploading is going to take some time. It’s going to be a lot quicker on the campus network where we have much higher upload speeds than you’re likely to get on a home connection.

Given that uploading can be a slow process, this is another reason to ensure that you’re being as efficient as your use-case demands when exporting your video.

Be sure to check the online copy of your video once it’s uploaded. It may take a while for whoever is hosting the video to process it before you can watch it. So be prepared to have to do even more waiting…

Videos uploaded to your Google Drive, or to a YouTube account will each have specific sharing permissions, that you can customize.