This is what is know as chroma subsampling. Almost all of the video you see on the web is encoded as YUV-420.
Something else worth noting is that many video streams are not full resolution. An example of an open source, mathematically lossless compressed codec is FFV1, developed by the makers of the ffmpeg software. So lossless codecs will allow you to retrieve the pixel data as it was originally, with no generation loss, but do not store the pixels as a simple stream of bytes. Other lossless encoding use more efficient algorithms, and the more efficient they are the more processing they generally require. An old lossless codec, Apple's Animation codec uses RLE encoding, which given the highly redundant nature of video streams gives fairly significant size reduction, at the overhead of more processing. It's a bit like wav, except that almost nobody uses it.Ī solution to the storage and transport problem is to compress the data mathematically - as you would compress other files that you need to restore perfectly. An example of an uncompressed codec is V210, developed by Apple, back when dinosaurs ruled the earth. Even though storage is cheap, that's still going to pose a problem just playing it back will be taxing. Given that a single frame of 1080p video has around 2.1 million pixels, each frame is going to require a about 7.8mB, and at 24 fps thats ~187mB per second, or 671gB per hour. At say, 10 bits per colour channel, each pixel will take 30 bits. The difference between uncompressed and lossless is that uncompressed just store the colour channels as a stream of bytes, similar to a PCM stream in audio. But there are also uncompressed and lossless codecs that store the raster in a mathematically lossless way, so that each pixel in the decoded video will have the same colour information as the encoded video. Matt provided a good description of RAW codecs, but they are not prevalent in video, other than as camera codecs that get transcoded before use. I'll illustrate by giving an example of the size of an uncompressed stream of video.įirst it might be worth noting the difference between RAW and uncompressed codecs, and uncompressed and losslessly compressed codecs. While a relatively cheap device has been able to deal with a stream of PCM audio since the eighties, even today you need fast storage and a decent system to play a stream of uncompressed video. The reason there is no widely used uncompressed video format, as there is for audio is that the data rate for uncompressed video is so colossal that uncompressed video is kinda useless.
0 kommentar(er)
