11/17/2023 0 Comments Editready to condense video sizeWe encode all the data for the first frame, using other compression methods along the way, but then we only encode the differences from one frame to the next up to the end of the Long GOP-lather, rinse, repeat. Essentially (and this is a fairly crude description) we take our incoming video and divide it into groups of usually 30 frames-this is called a Long Group of Pictures. One of the many tricks H264 has up its sleeve is, as I mentioned before, temporal compression. That’s a tad over two million pixels: if this was stored as uncompressed 10-bit 4:2:2 component video, every second would be about 166 megabytes-that’s almost 600 gigabytes per hour! Even this is not absolutely raw data: we’re doing a bit of whizzo math on the three colour channels to squeeze them into two colour difference channels and tossing out some of the colour data (that’s the 4:2:2 part-more on this later).Īt 4K, you’d be looking at about 2.3TB per hour and at 8K, nearly 10TB-clearly impractical for sticking on YouTube or broadcasting over the air! Accordingly, we have to turn to compression codecs like H264 to make things practicable for delivery. Imagine a single frame of video at 1920 x 1080. While there are several complementary compression techniques involved, the most important one for the purposes of illustrating this discussion is temporal compression. The mechanism behind H264 involves some ferociously complex mathematics that condenses the raw information coming off the sensor and reduces it into a viewable form that takes up little space. Many cameras record H264: we use it because it affords high quality at comparatively small file sizes. One of the most common question that gets asked on this subreddit usually goes along the lines of “why has my library grown to such a huge size?” To answer this, we are going to have to delve into some of the essential differences between the various video codecs we commonly encounter and why these differences exist.Īrguably the most common codec we come across is H264, and its more advanced cousin HEVC (aka H265-similar to H264 but with more cowbell).
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