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This page contains an incomplete list of things available in x264 for you to do. It's organized into sections covering various parts of x264.
- Sequential elimination (SEA), used for exhaustive search, might be more generally applicable to algorithms like UMH, by letting us skip a lot of SADs. The downside is we won't be able to use SAD_X4 anymore.
- (T)ESA is currently wrong for motion searches done on weightp duplicates. This effect is miniscule, but it still should be fixed.
- Hierarchical motion estimation might be a useful way to catch very long motion vectors without the cost of UMH or ESA. It might also help regularize motion.
- Somehow take into account the effect of motion vector decision on future blocks.
- Hierarchical motion estimation
- Approximations from lookahead MVs
- Iterative ME (as per Snow)
- Trellis motion estimation
- Make the early terminations smarter. Currently they're just hacks -- some statistical analysis might be useful.
- SAD (subme 1) i8x8 vs i4x4 decision is a bit bad. Can it be improved without significant speed loss?
- Can we find more ways to skip more motion searches in multiref?
- On extremely fast encoding settings, fast skip is actually kind of slow. But anything dumber (e.g. SAD) is completely useless. Is there some better balance that can be achieved here?
- Chroma-aware mode decision for B-frames?
- Psy-RD is a hack. It works, but it's a hack. If you apply QNS with Psy-RD as the metric, it goes way overboard and gives terrible results. This means that Psy-RD only works because normal mode decision is limited in the way it can modify the image to better suit the metric. Is there a way to make it better?
- Should RD be linear at all? Perhaps we should weight more heavily against low quality blocks and also try to ignore minuscule distortion that viewers can't see.
- Psy-trellis (and maybe psy-RD?) are too strong at very high QPs.
- Psy-trellis should be merged with Psy-RD. There are patches for this, but they probably won't be committed until psy-RD itself is fixed.
- RD should take into account local variance.
- Lambda should be varied on a per-DCT-block basis instead of a per-macroblock basis.
- Lambda should be picked independent of quantizer (i.e. with greater precision).
- Lookahead should be multithreaded, either by splitting the frame (sliced threads) or running multiple frame analysis calls at once.
- Temporal MV predictors in lookahead? There's a patch for these somewhere, but they biased heavily in favor of B-frames, likely by improving the motion search.