Stereo encoding method and apparatus, and stereo decoding method and apparatus

A stereo encoding apparatus, comprising:

• at least one processor;
• and
• one or more memories coupled to the at least one processor and storing programming instructions for execution by the at least one processor that, when executed by the at least one processor, cause the encoding apparatus to:
• perform downmix processing on a first left channel signal of a first frame and a first right channel signal of the first frame, to obtain a first primary channel signal of the first frame and a first secondary channel signal of the first frame;
• determine that a first frame structure similarity value between the first primary channel signal and the first secondary channel signal falls within a preset frame structure similarity interval;
• in response to determining that the first frame structure similarity value falls within the frame structure similarity interval, perform differential encoding on a first pitch period of the first secondary channel signal using an estimated pitch period value of the first primary channel signal, to obtain a first pitch period index value of the first secondary channel signal;
• and
• generate a to-be-sent stereo encoded bitstream according to the first pitch period index value of the first secondary channel signal.