Video Basic

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1) What is Video?

•Video, or moving image in general, is created from a sequence of still images called frames.

•By recording and then playing back frames in quick succession, an illusion of movement is created.

•Video can be edited by removing some frames and combining sequences of frames, called clips, together in a timeline.

2) What is a Video Format?

•A video format defines the way in which video is recorded and stored. It normally specifies:

=> Codec/compressor

=>Frame rate

=> Frame size

=> Frame aspect ratio

=> Pixel aspect ratio

=> Scanning method (interlaced or progressive)

• Common formats are DV, HDV and AVCHD.

3)What is a Codec (Compressor)?

• Codec is short for coder-decoder and describes the method in which video data is encoded into a file and decoded when the file is played back.

• Most video is compressed during encoding, and so the terms codec and compressor are often used interchangeably.

• Transcoding is the process of converting from one codec to another.

• Codecs can be Lossless, which means that they do not throw away any data, or Lossy, which means that data is lost during encoding.

• Lossless codecs are higher quality than lossy codecs, but produce larger file sizes.

***To find codec on your system follow the steps:

1) On the Help menu in Windows Media Player, select About Windows Media Player. If you don't see the Help menu, select Organize > Layout > Show menu bar.

2) In the About Windows Media Player dialog box, select Technical Support Information. Your web browser will open a page that includes a lot of detailed info about the related binary files, codecs, filters, plug-ins, and services installed on your PC. This info should help you troubleshoot problems.

4) What is a Frame?

• A frame is a single still image within a video clip.

• As with any digital image, a frame consists of pixels (picture elements), with each pixel representing a colour within the image.

•The higher the number of pixels, the more accurately an image can be represented. This is called resolution and is measured in megapixels.

5) What is Frame Size?

• Frame Size describes the size of a single video frame: width x height, measured in pixels.

• The width of the frame can vary depending on whether the pixels in the frame are square pixels or non-square pixels.

• An example: a DV-PAL 4:3 frame is 768 pixels wide (square pixels) or 720 pixels wide (non-square pixels). This is because a smaller number of pixels are required to create the same size frame on screen if each individual pixel is wider.

•Computer graphics use square pixels, whereas video cameras use non-square pixels. 

Therefore if creating graphics for video, use the square pixel frame size.

•A square pixel aspect ratio can be written as 1.0 (width÷height). All other values indicate non-square pixels.

6) What is Frame Aspect Ratio?

• Frame Aspect Ratio describes the relationship between the width and height of a single video frame.

• Video is landscape, so the width of a frame is greater than the height.

• Typical Frame Aspect Ratios for video are 4:3 and 16:9.

• Digital stills cameras often use 4:3 or 3:2.

• 4:3 is refered to as standard.

• 16:9 is referred to as widescreen, and is sometimes (inaccurately) called anamorphic. 

Some widescreen video is anamorphic, but not all.

7) What is Frame Rate?

• Frame Rate tells you how many frames per second there are when recording or playing video.

• Video cameras in Europe use 25 frames per second (fps). In USA & Japan 29.97fps or 30fps is used.

• Animation works by recording each frame individually (e.g. with a stills camera) and then playing them back at a frame rate.

• Animators often work with a lower frame rate (e.g. 12fps) so less frames are needed for the same length video clip.

• If you change the frame rate of a 12fps video clip to 25fps, e.g. by adding it to a 25fps editing project, each frame will be repeated to keep the clip the same duration.

8) What is Timecode?

• Timecode is how the duration of video is measured, and is divided into hours, minutes, seconds and frames, like so: HH:MM:SS:FF.

• An example: 00:01:22:06 means 1 minute, 22 seconds and 6 frames.

• It is recorded by the video camera as part of the video signal, and is used to navigate and locate video when editing.

9)What does Scanning Method mean?

• A video frame is displayed on a screen by scanning each horizontal line from left to right to form the image.

• Scanning method describes the way this is done, either by scanning first the odd lines, then the even lines (interlaced), or by scanning every line in order (progressive).


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