.ASF is a file format created by Microsoft, formerly known as Active Streaming Format or Advanced Streaming Format. ASF is specifically designed for streaming audio and visual content. ASF files are containers for the streaming media, and normally Windows Media Video or Windows Media Audio files are found within them. This format has been superseded by WMV.
An .asf file may contain video and audio, and can also contain metadata in the same way that MP3 files do. This allows the definition of artist, album etc. The file format allows streaming in a similar method to other formats, allowing the user to view the file once a certain amount of bytes have been downloaded. The file continues to download while the user watches. Due to it being designed for streaming, one disadvantage of ASF is that the maximum resolution is a relatively small 352x288.
MP4 files (MPEG-4 Part 14) are multimedia files. MP4 is a container format that can store video, audio and subtitle data (as well as more depending on content). Since stores like iTunes uses this container format, and it is used with iPod and PlayStation Portable (PSP), MP4 files have become more common.
MPEG-4 Part 14 or MP4, formally ISO/IEC 14496-14:2003, is a multimedia container format standard specified as a part of MPEG-4. It is most commonly used to store digital video and digital audio streams, especially those defined by MPEG, but can also be used to store other data such as subtitles and still images. Like most modern container formats, MPEG-4 Part 14 allows streaming over the Internet. A separate hint track is used to include streaming information in the file. The only official filename extension for MPEG-4 Part 14 files is .mp4.
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