Apple Final Cut Express HD Uživatelský manuál stáhnout pdf (Strana 12)

Appendix A: Video Formats Explained

Video is not just video-- there are many diﬀerent ways of storing it, whether on a tape,

on a computer, on a DVD, or on an iPod. e diﬀerent formats of storage are codecs,

as in to code and decode the video. ese codecs reduce the amount of data required to

store the video using clever mathematical techniques. Codecs generally do this by one

of two methods:

Intra-frame

Also called I-frame, this means that each frame (the individual pictures that make up a

movie) is compressed separately. e codec basically sees the video as a series of pictures, and deals with each

one independently of the ones around it. Intra-frame is usually preferable to inter-frame, as it’s easier for the

computer to work with while editing, but it also produces bigger le sizes and thus may require a more hard

drive storage to work with. Examples of intra-frame formats include: DV, DVCPRO, DVCPRO HD, and

ProRes 422.

Inter-frame

With ain inter-frame codec the frames are not only compressed individually, but also rely on each other to

determine the best method of compression. e codec looks at one frame, then looks at the next to see what’s

changed, and records only the changes instead of the whole frame. Inter-frame is often used by cameras to t

more footage onto the recording media (a tape, card, or hard disk), but is more diﬃcult to edit with, as the

computer has to work harder at decoding the frames. While less storage is required, more computational power

is requried, and therefore when editing inter-frame codecs newer, faster computers are required. Examples of

inter-frame codecs include: MPEG, H.264, AVCHD (uses H.264 codec), HDV (uses MPEG-2 codec).

Other elements that dene a codec include:

Resolution: the measure of pixels in the frame. Common resolutions are 720x480 (standard denition), and

1280x720 / 1920x1080 (high denition).

Target Bit Rate: how much of the video information can be conveyed over a period of time. Codecs can range

from just a few Mbits/sec to hundreds.

Frame Rate: e number of frames per second the codec can store.

Audio Channels: e number of audio channels a codec can contain, along with the audio bit rate (the higher,

the better) of those channels.

A Brief Introduction to Editing with Final Cut Express (work-in-progress v.3c) Page 12 of 14

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Apple Final Cut Express HD Uživatelský manuál Strana 12