BTEC CREATIVE MEDIA
Video Editing – the technical stuff
A note before we start on ORGANISATION On the computer, when you are creating projects, YOU MUST be organised! Get used to creating a clear organisation of folders on the hard drive and bins in the Premiere project window for all the different elements of your project – visuals (organised by shoot), music, foley sounds, graphics etc. All should be organised carefully both in your folder in the Movies folder on the Mac HD and within your project. We will be assessing your editing ability partly on how you organise your files. Part of this organisation is also about UNDERSTANDING VIDEO FILES AND OTHER FILES (EG GRAPHICS, MUSIC) FROM A TECHNICAL PERSPECTIVE. This sheet gives you that information.
Aspect Ratios The ASPECT RATIO is the width in relation to the height of a video. Old style TVs were 4:3. Newer TVs are wider-screen, often 16:9. Movies at the cinema are wider still.
Video Sizes DVD video is usually 720x576 pixels. The pixel count of HD (HIGH DEFINITION) video is usually 1280x720 (known as 720), or 1920x1080 (known as 1080) – that’s the Bluray standard. Obviously the bigger the numbers here, the bigger the file size for storage on your computer. Most of our camcorders shoot in 1080.
Frame Rate and Progressive/Interlaced Video When you set a camcorder or DSLR camera to shoot video, you’ll often have a series of ‘video quality’ settings to choose from. You’ll see, for example, 720:50p or 1080:25i etc. The first of these numbers is the video size, as above. The second number is the FRAME RATE – ie how many frames there are per second (fps). The higher this number the better the video will be at showing fast movement without it becoming a mushy blur, and the better it will be if you want to shoot slow motion. The ‘P’ or ‘i’ designation is about how the frames are shown. Progressive scan (‘p’) shows every frame one after the other. ‘Interlaced’ scan shows half the frame at any one moment, and
interlaces these half frames together so we see unified movement. Basically, ‘p’ is much better but produces files that are much larger. Our iMac video editing systems can now edit with 1080:50p as well as 1080:50i, although file sizes are very large so storage can become an issue. If you are using a camcorder or camera where you can set it to ‘p’ or ‘i’ shoot a sequence in each and see if you can tell the difference. Real film is shot at 24fps so some cameras offer the opportunity to shoot at this frame rate, although higher will give you smoother action. (There is more to making video look like film than just setting the frame rate). Annoyingly US and UK tv systems also use different frame rates. In the UK, the PAL system is 25fps and in the US, the NTSC system is 29.97fps.
File types and Compression There are various moving image/sound file types. These are the ‘containers’ in which video and audio are stored. Many of them are ‘compressed’ to make the file sizes as small as possible. Highly compressed file types are called ‘lossy’, whereas less compressed file types are called ‘lossless’. Uncompressed files are called ‘uncompressed’!) Professional setups use lossless or uncompressed file types (a common one is ProRes) but the file sizes can be huge. As the name implies, ‘lossy’ files do sacrifice some detail.
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• AVCHD is a domestic camcorder file type. It often has the suffix .mts It is highly compressed. • MOV is a video file type associated with Apple Quicktime. It has the suffix .mov. It is also compressed. • FLV and F4V are Flash video files. Flash is a technology used on the web (although becoming rarer). Again these files are lossy, compressed files. • MPEG – this is the file type used for DVDs. H.264 – closely related to MPEG and a commonly used standard
The issue of compression and file types is also important when considering AUDIO on its own. MP3 is heavily compressed and not a great option for video editing. Uncompressed audio files will give better quality. Uncompressed audio formats include AIFF and WAV. Use these where possible in preference to MP3.
Codecs If the file type is the container, then the CODEC is HOW the video and audio is compressed to get it inside, then decompressed to read it again, for example by an editing programme such as Premiere Pro. Codec actually means coding/decoding. A common codec, closely allied with MPEG formats, is H.264. In fact it is so popular that it is something of a standard codec to use for a wide variety of output situations. Since it is so useful, Adobe Premiere Pro treats it as a file type in its output menus.
Exporting/Distributing When EXPORTING finished products so that they can be played on particular devices (as DVDs or Blurays, on Youtube, mobiles or tablets etc) it is CRUCIAL to know what you are doing. Luckily most video editing software has a rage of export presents to help you here. The screen grab below shows less than half of the output options available for the popular H.264 codec in the drop down menu from Premiere Pro, for example!
Bitrate Bitrate is the rate at which a file processes information. The higher the bitrate the more powerful the computer you need. You may note that some Youtube videos look much better than others, even when both are 1080p. This is often because of the bitrate chosen to encode the video. See this link for a really good explanation of this, and details of how to get the best out of your videos when selecting export settings from Premiere Pro
http://www.youtube.com/watch?v=MnQDGQAI0yk