How can I detect whether a WAV file has a 44 or 46-byte header?

Question

I\'ve discovered it is dangerous to assume that all PCM wav audio files have 44 bytes of header data before the samples begin. Though this is common, many applications (ffmp

Answer 1

In addition to Radiodef's excellent reply, I'd like to add 3 things that aren't obvious.

1. The only rule for WAV files is the FMT chunk comes before the DATA chunk. Apart from that, you will find chunks you don't know about at the beginning, before the DATA chunk and after it. You must read the header for each chunk to skip forward to find the next chunk.

2. The FMT chunk is commonly found in 16 byte and 18 byte variations, but the spec actually allows more than 18 bytes as well. If the FMT chunk' header size field says greater than 16, Bytes 17 and 18 also specify how many extra bytes there are, so if they are both zero, you end up with an 18 byte FMT chunk identical to the 16 byte one. It is safe to read in just the first 16 bytes of the FMT chunk and parse those, ignoring any more. Why does this matter? - not much any more, but Windows XP's Media Player was able to play 16 bit WAV files, but 24 bit WAV files only if the FMT chunk was the Extended (18+ byte) version. There used to be a lot of complaints that "Windows doesn't play my 24 bit WAV files", but if it had an 18 byte FMT chunk, it would... Microsoft fixed that sometime during the early days of Windows 7, so 24 bit with 16 byte FMT files work fine now.

3. (Newly added) Chunk sizes with odd sizes occur quite often. Mostly seen when a 24 bit mono file is made. It is unclear from the spec, but the chunk size specifies the actual data length (the odd value) and a pad byte (zero) is added after the chunk and before the start of the next chunk. So chunks always start on even boundaries, but the chunk size itself is stored as the actual odd value.