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This made me think... Is that a misfeature or bug in the compression algorithm? Why wouldn't the video codec adapt appropriately? If lower res causes a more eve
by 0x0 13y ago
This made me think... Is that a misfeature or bug in the compression algorithm? Why wouldn't the video codec adapt appropriately? If lower res causes a more even and smooth image, why shouldn't it scale down?
- nitrogen 13y agoI had typed a lengthy introduction to an explanation, but realized I don't know exactly where all the bits are going in a high-res low-bitrate image. All I can say with confidence is that if you squeeze a high-resolution image into the same size as a low resolution image, the low resolution image will look better. The high resolution image will basically be reduced to storing DC coefficients, so you'll see these giant 16x16/8x8/4x4/etc. pixel blocks of solid color, with maybe a bit of pattern on them that barely correlates with what the original looked like. Maybe it comes down to the per-macroblock overhead; maybe fewer blocks total in the lower resolution image allows more bits to be allocated to frequency coefficients instead of DC offsets.
- 0x0 13y agoYeah, I've observed the effect, but it never occured to me that it doesn't (or shouldn't) have to be that way :) We should be able to demand codecs that are smarter and more adaptive :) It's hard to imagine why anyone would want a blocky highres lowbitrate stream if the lowres variants are always better, for a given timespan of video
- gmartres 13y agoThough this isn't implemented by the reference encoder yet, the VP9 bitstream supports this (encoding a downscaled frame and signaling to the decoder to upscale it before displaying it).