Package magic implements MIME type sniffing of data based on the well-known "magic" number prefixes in the file.
VideoExtensions are common video filename extensions that are not covered by mime.TypeByExtension.
HasExtension returns whether the file extension of filename is among extensions. It is a case-insensitive lookup, optimized for the ASCII case.
MIMEType returns the MIME type from the data in the provided header of the data. It returns the empty string if the MIME type can't be determined.
MIMETypeByExtension calls mime.TypeByExtension, and removes optional parameters, to keep only the type and subtype.
MIMETypeFromReader takes a reader, sniffs the beginning of it, and returns the mime (if sniffed, else "") and a new reader that's the concatenation of the bytes sniffed and the remaining reader.
MIMETypeFromReader takes a ReaderAt, sniffs the beginning of it, and returns the MIME type if sniffed, else the empty string.