H.264-to-H.265 video transcoding method and transcoder

The invention provides an H.264-to-H.265 video transcoding method which comprises an H.264 decoding process and an H.265 encoding process. According to the H.264 decoding process, code streams conforming to the H.264 standard are completely decoded into a pixel domain, and the encoding macro block type, the encoding block mode and the residual sum of each macro block of all frames I and the encoding macro block type, the motion vector, the reference frame and the residual sum of each macro block of all frames P are extracted in the decoding process. According to the H.265 encoding process, H.265 encoding is carried out according to the H.264 decoding result to obtain H.265 video, corresponding processing according to CTU setting and frame types is included, search branches are properly reduced, and encoding complexity is reduced. Therefore, video transcoding time can be effectively reduced under the condition of guaranteeing that video quality is slightly reduced and the code rate is slightly increased, and popularization of the H.265 standard and network bandwidth saving are facilitated.