Carl Zwanzig (12021-06-29): > Like the "Good/Fast/Cheap - Pick two" metaphor, you have hit the > quality/file-size/bandwidth trade-off. To keep the resolution at 4k and at > good-to-excellent quality, perforce the files and bit-rate will be large- if > you want the file to be smaller, even with very fancy encoding something > must be discarded, could be resolution, could be frame rate, could be > "quality".
Frame rate and resolution are both elements of quality. In principle, codecs are capable of skipping frames or flattening neighboring pixels, so they should be able to decide to reduce the frame rate or resolution if it is the best choice. But in practice, codecs are not that smart, and reducing the resolution will sometimes help. > There's also the point that in many cases, super high quality is effectively > wasted, for instance, 4k is only effective if the viewer has a 4k display; ... and excellent eyesight: for a normal/close viewing distance, the separation power of the central area of our eye is about the size of a pixel in a 2K video. Everything beyond that is only useful if we pause and look closely. > 5.1 sound is only effective if the listener has 5.1 playback equipment -and- > the sound was mixed for that. etc. This is true. But you also missed something: It is true that, unless we're using "-c:v kenjanoishi", in order to gain something, for example file size, we have to sacrifice something of equal value, and it is frequently quality. But there are other possibilities than quality. Compatibility is a possibility: the old file was playable by a DVD+DivX player from the 2010s, the new file is not, but it is smaller. Using a better codec or a more complex codec profile is a case of this. Processing power is a possibility: the old file took 2 hours to encode, the new file takes 10, but it will be smaller. Nimbleness is a possibility: the old file allowed to seek at any half second, the new file only allows to seek to scene changes, but it is smaller. This is something to remember. Video encoding is a complex task. Your advice was sound: for archival, better keep the original. Do not recompress to gain a measly 25%. But for viewing, adapt the quality compromise to the viewing conditions. Regards, -- Nicolas George
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