Methods and apparatus on transform and coefficient signaling

An electronic apparatus comprising:

• one or more processing units;
• memory coupled to the one or more processing units;
• and
• a plurality of programs stored in the memory that, when executed by the one or more processing units, cause the electronic apparatus to perform a method for video decoding, the method including:
• receiving a bitstream comprising a transform block, wherein the transform block includes a non-zero region and a zero-out region;
• determining whether any coding group of the transform block located within the zero-out region has a non-zero coefficient;
• in accordance with a determination that no coding group of the transform block located within the zero-out region has a non-zero coefficient:
• receiving, from the bitstream, a value for a multiple transform selection (MTS) index;
• and
• applying respective inverse transforms to transform coefficients of the transform block in horizontal and vertical directions based on the value of the MTS index.

A non-transitory computer readable storage medium storing bitstream to be decoded by a method for video decoding, the method including:

• receiving the bitstream comprising a transform block, wherein the transform block includes a non-zero region and a zero-out region;
• determining whether any coding group of the transform block located within the zero-out region has a non-zero coefficient;
• in accordance with a determination that no coding group of the transform block located within the zero-out region has a non-zero coefficient:
• receiving, from the bitstream, a value for a multiple transform selection (MTS) index;
• and
• applying respective inverse transforms to transform coefficients of the transform block in horizontal and vertical directions based on the value of the MTS index.