As the same with H.264/AVC, HEVC/H.265 is divided into Video Coding Layer(VCL) and Network Abstraction Layer（NAL). Original video will be encoded into video data through the VCL layer, and then be Encapsulated into many NAL packets through the NAL layer. The distinction between HEVC/H.265 stream and H.264/AVC stream in the application process lies in the NAL layer, HEVC/H.265 stream offers help for thoses developers who are concerned about HEVC/H.265 application without interest in HEVC/H.265 coding technology.

HEVC/H.265 uses hybrid coding framework similar to H.264/AVC.The video is divided into blocks, and turns into stream by predicting, transforming, quantifying and entropy coding for transmission, and then it will be entropy decoded, inverse quantified,inverse transformed and predicted at the encoding side and decoding side. At last, the image obtained will be Loop filtered. The biggest difference from H.264/AVC is that HEVC/H.265 contains Deblocking and SAO while H.264/AVC only contains Deblocking.

The larger image block may be a CU (Coding Unit) in HEVC/H.265, it can also be divided into four small CU, the blocks coressponding to small CU may be divided into four smaller Cu, until the smallest CU explained in stream. In HEVC/H.265, a CU can not be smaller than 8x8. However, it can explain that smallest CU may be larger than 8x8 in the stream. CU structure can be abstracted as a quadtree structure. A large block stands for flat areas, while a small block stands for complex areas after encoding, thus improving the coding efficiency.

In a hybrid coding framework, the elimination of redundancy in a video is completed by the prediction module largely. HEVC/H.265 adopts more elaborate and complex prediction algorithm than H.264/AVC in prediction module, which provides a great contribution to improvment of compression ratio.

Compared with H.264/AVC, HEVC/H.265 uses a larger transformation. Blocks of each size will be DCT transformed, while DST transformation will be used in the 4x4 intra luminance blocks. In the quantization, HEVC/H.265 introduces the new technology of the sign data hiding, increases coding complexity, but does not affect the complexity of the decoding.

HEVC//H.265 entropy coding, loop filter, DPB (Decoded Picture Buffer) management changes