Overview Video Formats
The term video format describes the specification of a video concerning: its image resolution, the aspect ratio, the image refresh rate and the colour depth.
Image Resolution
The image resolution defines the number of pixels. It is defined in height x width.
In the area of video conferences, there are resolutions with unique names, which are derived from the ITU standards.
| Image Format | Resolution (x,y) | Supported by Standards | Bit Rate (Bit/s) (unimpressed) |
||||||
|---|---|---|---|---|---|---|---|---|---|
| 10 Images/s | 30 Images/s | ||||||||
| b/w 8Bit |
Colour 24Bit |
b/w 8Bit |
Colour 24Bit |
||||||
| SQCIF | 128 | 96 | - | H.263 | H.264 | 1.0 | 2.8 | 2.9 | 8.6 |
| QCIF | 176 | 144 | H.261 | H.263 | H.264 | 2.0 | 6.0 | 5.9 | 17.8 |
| 1/4 NTSC | 320 | 240 | - | - | - | 6.0 | 18.0 | 18.0 | 54.0 |
| CIF | 352 | 288 | H.261 | H.263 | H.264 | 7.9 | 23.8 | 23.8 | 71.2 |
| 1/4 PAL | 384 | 288 | - | - | - | 8.6 | 26.0 | 25.9 | 77.8 |
| VGA / NTSC | 640 | 480 | - | - | - | 24.0 | 72.0 | 72.0 | 216.0 |
| 4 CIF | 704 | 576 | - | H.263 | H.264 | 31.7 | 85.0 | 95.0 | 285.2 |
| PAL | 768 | 576 | - | - | - | 34.6 | 103.6 | 103.7 | 311.0 |
| SVGA | 800 | 600 | - | - | H.264 | 38,4 | 115,2 | 115,2 | 345,6 |
| XGA | 1024 | 768 | - | - | H.264 | 62,9 | 188,7 | 188,7 | 566,2 |
| SXGA | 1280 | 1024 | - | - | H.264 | 104,9 | 314,6 | 314,6 | 943,7 |
| WXGA (16:9) | 1024 | 576 | - | - | H.264 | 47,2 | 141,6 | 141,6 | 424,7 |
| WXGA (8:5) | 1280 | 800 | - | - | H.264 | 81,9 | 245,8 | 245,8 | 737,3 |
| UXGA | 1600 | 1200 | - | - | H.264 | 153,6 | 460,8 | 460,8 | 1382,4 |
| QXGA | 2048 | 1536 | - | - | H.264 | 251,7 | 755,0 | 755,0 | 2264,9 |
| 720p | 1280 | 720 | - | - | H.264 | 73,7 | 221,2 | 221,2 | 663,6 |
| 16 CIF | 1408 | 1152 | - | H.263 | H.264 | 129,8 | 389,3 | 389,3 | 1167,9 |
| 1080p | 1920 | 1080 | - | - | H.264 | 165,9 | 497,7 | 497,7 | 1493,0 |
Tab.1: Some selected image formats for video conferences
The H.264 standard only defines maximum upper limits for the image formats.
Additional information:
Aspect Ratio
The aspect ratio defines the amount of pixels vertically to the amount of pixels horizontally.
In practical use, the variants 4:3, 5:4, 16:9 and 16:10 have established themselves in IT.
Display of different formats is achieved by stretching or compressing the received image. This can lead to information loss or image distortions.
The industry has since expanded the standards by other (non-standardised) alternatives:
- Q - Quarter
- Q - Quad
- W- Wide (for display in the area between 16:9 and 16:10)
- U - Ultra (for display in the 4:3 area)
- H - Hex (sixteen times)
All variants that are smaller than VGA are currently only used for smart phones.
Image Refresh Rate
The image refresh rate indicates the number of single images per second which are replayed or recorded in this time unit.
It is specified in Hertz (Hz) or frames per second (fps). At more than 30 images per second, the human eye perceives them as a fluent sequence.
Colour Depth
The colour depth signifies the brightness and colour values of an image. The values are saved together with the image.
The colour depth is specified in bit. The RGB colour space is used most often, where the resulting visual display is created with the help of the colours red, green and blue. In the case of 24 bit colour depth, 8 bit are used for each channel, which, in theory, facilitates 16,777,216 different colours.