Files ending in H264 contain a video stream encoded using the H.264 method.
This process is also referred to as H.264 / MPEG-4 Part 10 or AVC (Advanced Video Coding) and is a standard for efficient, lossy compression of video data. It is mainly used for high-resolution material. For example, H.264 is used on BluRay discs, as a transmission format of HD channels and in Flash videos.
The bitstream contains only the encoded data without any further information, such as refresh rate or resolution. The file also contains no audio.
The extension is not necessarily recognized, but any player playing H.264 should be able to view the file. Occasionally, however, an H.264-capable container, such as MP4 or FLV because of the content with the extension H264 marked. This is wrong.