Methods of video picture coding with sub-block merge simplification and related apparatuses

A method for temporal motion vector prediction of a current picture in a series of pictures of a video sequence, the method comprising:

• determining, for a current block of the current picture, whether any one of:
• left, top, top-right and left-bottom spatial neighboring blocks of the current block in the current picture uses a collocated picture as a reference picture;
• using a motion vector of the one of the spatial neighboring blocks as a temporal vector of the current block, when the determination is that one of the left, top, top-right and left-bottom spatial neighboring block uses a collocated picture as a reference picture;
• and
• wherein the determining whether any one of:
• left, top, top-right and left-bottom spatial neighboring blocks of the current block in the current picture uses a collocated picture as a reference picture is performed by checking only the left spatial neighboring block of the current block in the current picture without reference to any listing of spatial neighboring blocks in any merge list.