motion estimation in x264

[tono1234]

Hi people,

Is there any document that explains how motion estimation in is done in x264? I would assume that it uses some kind of fast motion estimation (i.e. not full search), but I would appreciate if someone could point me to a document that describes this process, if such a document exists.

Thanks

[Dark Shikari]

This overview (http://akuvian.org/src/x264/overview_x264_v8_5.pdf) has some information, but it's outdated.

x264 has 5 fullpel motion estimation modes:
radius-1 diamond,
radius-2 hex (default),
UMH (somewhat similar to JM),
exhaustive (implemented fast via sequential elimination),
and Hadamard exhaustive (implemented approximately via thresholded sequential elimination).

This mostly overlooks the main power behind x264's motion search (11 predictors including single-level hierarchical search, qpel-RD).

If you want more specific details, ask on #x264dev on Freenode IRC.

[tono1234]

Thanks for your answer. If I will have more detailed questions about the implementations I will ask at your proposed place. Generally I am just interested if any kind of performance/complexity measurement between Hexagon search and UMH exist? According to my understanding the Hexagon search suffers from the problem that it will more likely stuck in the local minimum, while the UMH is more robust in that sense, but also more complex. Is my understanding correct?

Thanks

[Dark Shikari]

Thanks for your answer. If I will have more detailed questions about the implementations I will ask at your proposed place. Generally I am just interested if any kind of performance/complexity measurement between Hexagon search and UMH exist? According to my understanding the Hexagon search suffers from the problem that it will more likely stuck in the local minimum, while the UMH is more robust in that sense, but also more complex. Is my understanding correct?Yes, that is true of all gradient descent searches (dia, hex, similar).

[uw_mike]

hi,

are there any documents explaining how full search motion estimation is done?

mike

[campo88]

Hi

I have been reading about block motion estimation algorithms such as the three step search, four step search, diamond search, new three step search, adaptive rood pattern search etc

How comes these are not an option with x264.

Do the hexagon and multi-hex have different names they are known by?

[imcold]

There is a diamond search option in x264; as for the others: probably worse performance/speed than what's already implemented.