sox_ng wiki - File-Formats

Formats

Audio files come in many formats like wav, mp3 and so on, and each of these may support different encodings inside the file. This article is about the overall formats.

When decoding, SoX recognizes what the format of the audio file is in src/formats.c:open_read() in this order:

• the name passed as -t before the input filename
• the filename's extension
• the contents of the file's header, necessary when reading a file with no extension, with an unknown extension or from standard input or a pipe (the magic contents it knows are listed in auto_detect_format() in src/formats.c)

It looks these up in the names field of all the available format handlers and uses that format handler to decode the file. If several format handlers can decode the same file format, it chooses the first one in its list of handlers, which are in the order listed in src/formats.h:

• first, the always built-in handlers
• then, the handlers that could be dynamically loaded but that were built in when the version of SoX in use was compiled
• last, the dynamically-loaded handlers

When encoding, either it must recognise the filename extension or you must say -t whatever, where whatever is a filename extension that it knows: those listed by sox_ng --help at the AUDIO FILE FORMATS: line.

Note that filename extensions and handler names do not always correspond. For example, ".amrnb" files are handled by the amr-nb handler and many filename extensions can be handled by the sndfile and ffmpeg handlers.