Last update : August 2013, 2013
Sometimes it’s necessary to crop or padd a video to change the aspect ratio and the resolution. The size of a video image is measured in pixels for digital video, or horizontal scan lines and vertical lines of resolution for analog video. In the digital domain standard-definition television resolution is specified as 720/704/640 ×480 for NTSC and 768/720 × 576 for PAL or SECAM. However in the analog domain, the number of visible scanlines remains constant (486 NTSC/576 PAL) while the horizontal measurement varies with the quality of the signal: approximately 320 pixels per scanline for VCR quality, 400 pixels for TV broadcasts, and 720 pixels for DVD sources. Aspect ratio is preserved because of non-square pixels.
High-definition televisions are capable of resolutions up to 1920 ×1080 pixels.
Aspect ratio describes the dimensions of video screens and video picture elements. All popular video formats are rectilinear, and are described by a ratio between width and height. The screen aspect ratio of a traditional television screen is 4:3. High definition televisions use an aspect ratio of 16:9.
Some common used video resolutions and aspect ratios are :
- 128 : 96 > 4 : 3
- 176 : 144 > 11 : 9
- 240 : 176 > 4 : 3
- 320 : 240 > 4 : 3
- 352 : 288 > 11 : 9
- 480 : 272 > 16 : 9
- 640 : 480 > 4 : 3
- 720 : 480 > 3 : 2
To keep the aspect ratio of a video without distortion when changing the resolution, you often need to crop or to padd the video (delete or add pixels on top, bottom, left and right side). I use the great video-tool Super from eRightSoft to do this job. The current version is v2013.build.57 released on July 13, 2013.