When processing images without complicated color and luminance changes, it'll divide macroblocks into sub-macroblocks of 8x8, 4x8, 8x4, and 4x4. It supports 9 directional prediction modes and 4 macroblock partitions (16x16, 16x8, 8x16, and 8x8). The intra prediction methods of H.264 are pretty flexible.
And intra prediction is to predict the luminance and color components of blocks by referring to the surrounding and previously-codec pixels within the current image. Each frame is divided into pixel blocks of which are called macroblocks. It is to predict image data from a micro perspective. While intra prediction is the advanced feature of H.264.
Inter prediction has already been applied in previous H.26x series and MPEG-x series standards though not as efficiencient as H.264. The more frames between I-frames, the longer the GOP. A typical structure could be IBBPBBPBBI or IBBPBBPBBPBBI.
When we take a look at the history of H.264, we'll find that it wasn't born with the talent of compressing all videos at a high compression ratio. And it is the most accepted codec implemented in almost all multimedia industries including DVD/BD, HDTV, YouTube video, live streaming, broadcasting, video recording, etc. Videos (1080p and 4K) compressed by H.264 are relatively easier to save, compress, and deliver via the network. H.264 was created in 2003 and has made great improvements in compressing efficiency and coding algorithm by inter-pictures prediction and motion compensation tech. And that's why this standard is often referred to as MPEG-4 Part 10, Advanced Video Coding, or MPEG-4 AVC, which clearly illustrates both sides of its developers. The partnership effort is also known as the JVT (Joint Video Team) Project. H.264, one of the video coding standards, is co-developed by ITU-T VCEG (Video Coding Experts Group) and MPEG (Moving Picture Experts Group) from ISO/IEC JTC1.
Thus video codec standardization comes to enable different software and hardware manufacturers to work under general video compressing rules, for example, H.26x from VCEG, VC-1 from the Society of Motion Picture and Television Engineers (SMPTE), and VPx from Google. But there are too many methods to achieve this which may make it a mess. It is impossible or extremely hard to record, store, or transmit a video without compression for it has a huge amount of data to process. What Is H.264/AVC (Advanced Video Coding) Today, we'll make a deep review of this codec from a contemporary perspective including how it came up, how it works, where it is now, and where it is going.
H.264, also known as Advanced Video Coding (AVC), even though born almost twenty years ago, still stays the mainstream in the era of multiple video codecs co-existing where we can also see like HEVC/H.265, VP9, AV1, and the emerging H.266/VVC.