x264: Denotes a free, cross-platform Codec for the video format H.264 and is released under the GNU license. As an H.264 encoder, x264 works much more efficiently than codecs based on the simpler MPEG-4 ASP (e.g. the DivXcodec up to v6), or such encoders that are even older MPEG-2-Use procedure.
This means that x264 compared to previous codecs given Data rate delivers a better image quality or achieves greater compression for the given quality. x264 is based on the most complex and powerful profile, the High Profile, of the H.264 standard (details in the relevant article). In addition, x264 is able to carry out certain calculations in parallel, so that symmetrical multiprocessor systems can be optimally utilized. However, some functions of the H.264 standard have not (yet) been implemented in the x264 codec, such as the error correction of the baseline profile. It should also be noted that x264 - like any H.264 codec - is significantly more computationally intensive than the simpler MPEG-4 ASP-based codecs.
Encoding therefore requires more time and greater demands are placed on the system for playback. Playback with processors below 800 MHz can therefore cause problems, especially if they do not have the SSE instruction set. In contrast to XviD or DivX, for example, the x264 codec in the official version does not contain one Decoder. Additional software is therefore required in order to be able to play videos compressed with x264 on the PC. Since such videos correspond to the H.264 standard, you can theoretically use any H.264-compatible decoder.