1. H.264 and H.265 representation

 

H.265 is a new video coding standard developed by ITU-T VCEG after H.264. The H.265 standard revolves around the existing video coding standard H.264, retaining some of the original technologies, while improving some related technologies. The new technology uses advanced technology to improve the relationship between code stream, encoding quality, delay and algorithm complexity to achieve optimal settings. Specific research contents include: improving compression efficiency, improving robustness and error recovery capabilities, reducing real-time delay, reducing channel acquisition time and random access delay, and reducing complexity. Due to the optimization of the algorithm, H264 can realize standard-definition digital image transmission at a speed lower than 1Mbps; H265 can realize the transmission of 720P (resolution 1280*720) ordinary high-definition audio and video transmission at a transmission speed of 1~2Mbps.

 

H.265 is designed to transmit higher-quality network videos under limited bandwidth, and can play videos of the same quality with only half of the original bandwidth. This also means that our smart phones, tablets and other mobile devices will be able to directly play 1080p full HD videos online. The H.265 standard also supports 4K (4096×2160) and 8K (8192×4320) ultra-high-definition video. It can be said that the H.265 standard allows network video to keep up with the "high resolution" of the display screen.

 

H.264, also the tenth part of MPEG-4, was proposed by the Joint Video Team (JVT) jointly formed by the ITU-T Video Coding Expert Group (VCEG) and the ISO/IEC Moving Picture Expert Group (MPEG) The highly compressed digital video codec standard. This standard is usually called H.264/AVC (or AVC/H.264 or H.264/MPEG-4 AVC or MPEG-4/H.264 AVC) and clearly states its developers.

 

The big advantage of H.264 is that it has a high data compression ratio. Under the same image quality, the compression ratio of H.264 is more than 2 times that of MPEG-2 and 1.5 to 2 times that of MPEG-4. For example, if the size of the original file is 88GB, it will become 3.5GB after being compressed by the MPEG-2 compression standard, and the compression ratio will be 25:1, while it will become 879MB after being compressed by the H.264 compression standard, from 88GB to 879MB. The compression ratio of H.264 reaches an astonishing 102:1. Low bit rate (Low Bit Rate) plays an important role in the high compression ratio of H.264. Compared with compression technologies such as MPEG-2 and MPEG-4 ASP, H.264 compression technology will greatly save users' download time. And data traffic charges. It is especially worth mentioning that H.264 has a high compression ratio while also having high-quality and smooth images. Because of this, H.264 compressed video data requires less bandwidth during network transmission. Also more economical.

 

2. What is the difference between H.265 and H.264

 

Before discussing the enhancements and advantages of H.265, let's take a look at H.264. H.264, also known as MPEG-4 AVC (Advanced Video Codec, video coding), is a video compression standard and also a widely used high-precision video recording, compression, and distribution format. Because H.264 is a codec standard for Blu-ray discs, all Blu-ray players must be able to decode H.264. More importantly, because Apple resolutely abandoned Adobe's VP6 encoding and chose H.264, this standard has also entered millions of households with hundreds of millions of iPads and iPhones, and has become the current video encoding field. Lord, occupies more than 80% of the share. H.264 is also widely used in fields such as network streaming media data, various high-definition TV broadcasts, and satellite TV broadcasts. Compared with the previous coding standards, H.264 has some new features, such as motion compensation for multiple reference frames, variable block size motion compensation, intra-frame prediction coding, etc. By using these new features, H.264 has more features than other coding standards. High video quality and lower bit rate have also been recognized by people and widely used.

 

The coding architecture of H.265/HEVC is roughly similar to that of H.264/AVC. It also mainly includes: intra prediction, inter prediction, transform, quantization, Modules such as deblocking filter and entropy coding. However, in the HEVC coding architecture, the whole is divided into three basic units, namely: coding unit (CU), prediction unit (PU) and transformation unit (TU).

 

Third, why H.265 is better than H.264

 

Compared with H.264/AVC, H.265/HEVC provides more different tools to reduce the bit rate. In terms of coding unit, the size of each macroblock (MB) in H.264 is a fixed 16x16 Pixels, and the coding unit of H.265 can be selected from a small 8x8 to a large 64x64. Areas with little information (the color change is not obvious, such as the red part of the car body and the gray part of the ground) are divided into larger macro blocks, and the codewords after encoding are less, and the areas with more details (tires) are divided into macro blocks The blocks are correspondingly smaller and larger, and there are more codewords after encoding. This is equivalent to focusing on the image, thereby reducing the overall code rate and improving the coding efficiency accordingly. At the same time, the H.265 intra prediction mode supports 33 directions (H.264 only supports 8), and provides better motion compensation processing and vector prediction methods.

 

Repeated quality comparison tests have shown that under the same image quality, compared with H.264, the size of the video stream encoded by H.265 is reduced by approximately 39-44% compared to H.264. Due to different quality control methods, this data will change accordingly. The data obtained through subjective visual testing shows that when the bit rate is reduced by 51-74%, the quality of H.265 coded video can be similar to or better than H.264 coded video, which is essentially better than expected The signal-to-noise ratio (PSNR) is better. The evaluation criteria of these subjective visual tests cover many disciplines, including psychology and human visual characteristics. The video samples are very extensive. Although they cannot be the final conclusion, they are also very encouraging results.

 

The current HEVC standard has three modes: Main, Main 10 and Main Still Picture. Main mode supports 8bit color depth (that is, each of the red, green, and blue colors has 256 chromaticities, a total of 16.7 million colors), Main 10 mode supports 10bit color depth, which will be used on Ultra HDTV (UHDTV). The first two restrict the chroma sampling format to 4:2:0. It is expected that the standard will be expanded in 2014, and it will support 4:2:2 and 4:4:4 sampling formats (that is, providing higher color reproduction) and multi-view coding (such as 3D stereo video coding).

 

In fact, the H.265 and H.264 standards have some overlap in various functions. For example, the Hi10P part of the H.264 standard supports 10-bit color depth video. On the other hand, the H.264 part (Hi444PP) can also support 4:4:4 chroma sampling and 14-bit depth. In this case, the difference between H.265 and H.264 is that the former can use less bandwidth to provide the same function, at the cost of the computing power of the device: H.265 encoded video requires more computing power To decode. At present, a chip that supports H.265 decoding has been released-Broadcom of the United States (Broadcom) released a Brahma BCM7445 chip at the CES exhibition in early January this year. It is a quad-core processor with a 28-nanometer process. It can simultaneously transcode four 1080P video data streams or analyze H.265 encoded ultra-high-definition video with a resolution of 4096×2160.

 

The birth of the H.265 standard is to transmit higher quality network video under limited bandwidth. For most professionals, the H.265 coding standard is not unfamiliar. It is a video coding standard developed by ITU-TVCEG after H.264. The H.265 standard mainly revolves around the existing video coding standard H.264. In addition to retaining some of the original technologies, it adds the ability to improve the relationship between bitstream, coding quality, delay, and algorithm complexity. Related technology. The main content of H.265 research includes improving compression efficiency, improving robustness and error recovery capabilities, reducing real-time delay, reducing channel acquisition time and random access delay, and reducing complexity.