The Flash Video format is a video format defined by Adobe Systems. Flash Video has been accepted as the default online video format by many sites. Notable users of it include YouTube, Hulu, VEVO, Yahoo! Video, metacafe, Reuters.com, and many other news providers. Flash Video is viewable on most operating systems except iOS, via the Adobe Flash Player and web browser plugin or one of several third-party programs.
Flash Video FLV files contain video bit streams which are a proprietary variant of the H.263 video standard, under the name of Sorenson Spark (FourCC FLV1). Sorenson Spark is an older codec for FLV files but it is also a widely available and compatible one, because it was the first video codec supported in Flash Player. The Flash Video FLV file format supports two versions of a so called 'screenshare' (Screen video) codec which is an encoding format designed for screencasts. Both these formats are bitmap tile based, can be lossy by reducing color depths and are compressed using zlib. The second version is only playable in Flash Player 8 and newer - Audio in Flash Video files is usually encoded as MP3. However, audio in Flash Video FLV files recorded from the user's microphone use the proprietary Nellymoser Asao Codec. FLV files also support uncompressed audio or ADPCM format audio.
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AAC is similar to MP3. It essentially cuts out, or compresses, information that the human ear cannot pick up thereby making digital files smaller and more easily managed and therefore quicker to download. AAC is about half the size of MP3 but with better quality. It is at least one tenth the size of CD digital data. Apple are the biggest users of this format and if you have an iPod or iPhone then you will have come across this format as it is iTunes default audio format.
AAC is similar in concept to MP3 but goes further. It too compresses digital audio files but to a bigger degree. It is also part of the MPEG-4 standard, it is most widely used to create small digital audio files. The current variant is specified in ISO/IEC standard 14496-3. Like MP3, AAC is a lossy algorithm. The human hearing system cannot hear quiet sounds in the presence of loud sounds of a similar frequency; for example, a voice conversation cannot be heard while an aeroplane flies low overhead. This is known as auditory masking, this allows the discarding of data with minimal loss of quality.
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