Methods of video content complexity estimation, scene change detection and video encoding are provided. The video content complexity estimation and the scene change detecting are performed before a video encoding loop is processed. The method of video content complexity estimation includes calculating an absolute difference value diffi of the ith pixel between a current frame and a reference frame, a mean value mean(R) of pixel region R, a deviation value deviation(R) of pixel region R, a complexity value X of a target frame and an adjusted complexity Ĉtarget of the target frame by using equations mean ⁢ ⁢ ( R ) = 1 NM ⁢ ∑ i ∈ R ⁢ diff i , ⁢ deviation ⁢ ⁢ ( R ) = ∑ i ∈ R ⁢ abs ( diff i - mean ( R ) ) , ⁢ X = ∑ R ∈ frame ⁢ mean ⁢ ⁢ ( R ) · deviation ⁢ ⁢ ( R ) and Ĉtarget=a·X/b, respectively. Wherein, R represents N*M pixel region, a=b·SADtarget/X, b is power of 2 and SADtarget represents a true motion compensation sum of absolute difference for the target frame.