H.264 is a particular codec for MPEG-4 and is also known as MPEG-4 AVC (Advanced Video Coding) is the most recent standard and is designed to permit Internet streaming with less bandwidth requirements than MPEG-2 or MPEG-1.
H.264 also known as AVC (Advanced Video Coding) is a particular codec and is identical with MPEG-4 part 10. MPEG-4 AVC is a required video format for Blu-Ray disks. It is an advanced format that can achieve up to 4 hours on a standard disk at full resolution. Blu-Ray requires support for 3 video Codecs, in addition to AVC it must support MPEG-2 (H.262 SD) and VC-1. H.262 is the DVD standard also known as Standard Definition (SD). Players can usually also play audio CD's.
H.264 can achieve full H.262 capabilities so it is the new universal standard. However, the capabilities are still changing so most implementations can only achieve a certain subset of H.264.
See How it works for an explanation of the layout of an H.264 file.
H.265 also known as HEVC (High Efficiency Video Coding) is intended as a successor to H.264 AVC. It has double the compression for the same quality level or can alternatively be used to provide substantially improved video quality at the same bit rate. It can support 4K UHD and even up to 8K UHD and resolutions up to 8192 x 4320. It uses a much more complex computer intensive encoding utilizing large block sizes to accomplish higher compression. It replaces the 16 x 16 macroblocks with variable sizes up to 64 x 64 pixels. It does not support interlace although there are external workarounds available. See http://en.wikipedia.org/wiki/High_Efficiency_Video_Coding for more details. Some newer Blu-ray players support this format. They will be identified as 4K or UHD capable.
 How HEVC encode works
How are video files twice as efficiently coded as previous video coding standards?
Most of the power of video compression standards comes from a technique known as motion compensated prediction. Blocks of pixels are encoded by making reference to another area in the same frame (intra-prediction), or in another frame (inter-prediction). Where H.264/AVC defines macroblocks up to 16×16 pixels, HEVC can describe a much larger range of block sizes, up to 64 x 64 pixels.
HEVC allows predicted blocks to be coded in different block sizes than the residual error. Each top level coding unit (or CTU) is first coded as a prediction quad-tree, where at each depth the encoder decides whether to encode with merge/skip, inter, or intra coding. The residual from those predictions is then coded with a second quad-tree which can optionally have greater depth than the prediction quad-tree. For instance, this allows the residual error from a 32×32 inter coded coding unit (CU) to be represented by a mixture of 16×16, 8×8, and 4×4 transforms.
HEVC can encode motion vectors with much greater precision, giving a better predicted block with less residual error. There are 35 intra-picture directions, compared with only 9 for H.264/AVC.
- HEVC includes Adaptive Motion Vector Prediction, a new method to improve inter-prediction.
- An improved deblocking filter
- Sample Adaptive Offset – an additional filter that reduces artifacts at block edges