Why compression is so important?
To record a video of screen activities, the amount of data could be very huge without compression. Assume the size of screen is 1024x768, which is the smallest desktop resolution nowaday, to take a video of 1 minute could cost:
1024 x 768 x 3(RGB) x 60(s) x 2(frames per sec) = 283115520B = 276480KB = 270MB
A 1TB hard-drive can only store about 54 hours of such raw video, as well as it also taking about 15 minutes to send 1 minutes data via 1M band-width internet. A good compression method is nessesary. It will ensure a smaller file size, which means less space needed for storage and less time on sharing. And SSCV3 is the compression method specially designed to target the video recorded from screen.
What are the common ways to compress screen video in other softwares?
General screen recording software and remote controlling software contains compression abilities based on LZW. This function usually involves three steps:
- 1. Low the colour depth from 24 bits to 16 bits, or even 8 bits.
- 2. Use lossless compression, usually LZW, to compress one frame.
- 3. In following frames, do a simple compression on the changed area between this frame and the last frame.
Other softwares may even uses standard MPEG/H264 codecs to compress screens as well. However, neither LZW nor MPEG options are the best solutions for compressing a video like a screen, which is composed by different types of content, text, photo, icons..,etc. The LZW method may have better compression ratio on text and icons but it is bad for photos and animations. In other hand, MPEG/H264 have better performance on photos but working poor on text and icons. A specialised method is required to achieve great compression.
Why SSCV3 works better than other methods?
Targeting screen recording video, multiple technologies are used in SSCV3 to improve compression ratio and the quality.
Contents awareness compression
The screenshot will be analysed by the algorithm and be separated into different areas by its type. e.g photo, text, icon.., etc. Then the different compression methods will be applied targeting each type of them to achieve maximal compression ratio and efficiency.
Deep cache for windows
When a window has been deactivated and hidden behind, SSCV3 can still remember its image data for a while. When this window has been popped up again, since it is remembered by the codec, it would not bring extra data. The SSCV3 can keep as deep as 10 layers of image to cache most windows switching activities, that brings significant increasing of the compresison ratio.
Scrolling detecting
SSCV3 can detect scrolling movements on screen, for example, scrolling of a webpage. This detected movement will be used by encoder to predict pixels between frames, that improves the compression ratio further more.
Comparing to SSCV2 and other video codec
The
precious v2 codec was developed 16 years ago when the
up-to-date technologies of text rendering did not exist. The new text rendering technologies include 'Anti-alias' and 'Cleartype' , both are designed to reduce jaggies of pixels that make on-screen text look better.
However the text,which
are rendered by new technologies, will be classified as the type of 'icon' instead of 'text' in the v2 codec. The reason of that is, instead of black and white, multiple colors are used to render the text. Therefore the v2 codec has to spend more bits to compress them.
In the new v3 codec, a new type of content called 'Anti-alias text' is introduced into the
algorithm.By adding that, the compression ratio on text area is improved a lot. Plus on the new 'scrolling detection' technology, the v3 codec can achieve 2 times higher compression ratio compared to the v2 codec, with the same encoding/decoding speed. Compared to the most common H264 codec (MP4 video), the v3 codec can achieve about 3-4 times higher compression ratio (targeting screen recording video) with much faster running speed.
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