Types of IR codes

The IRremote library treats the different protocols as follows:

NEC: 32 bits are transmitted, most-significant bit first. (protocol details)

Sony: 12 or more bits are transmitted, most-significant bit first. Typically 12 or 20 bits are used. Note that the official protocol is least-significant bit first. (protocol details) For more details, I've written an article that describes the Sony protocol in much more detail: Understanding Sony IR remote codes.

RC5: 12 or more bits are transmitted most-significant bit first. The message starts with the two start bits, which are not part of the code values. (protocol details)

RC6: 20 (typically) bits are transmitted, most-significant bit first. The message starts with a leader pulse, and a start bit, which is not part of the code values. The fourth bit is transmitted double-wide, since it is the trailer bit. (protocol details)

For Sony and RC5/6, each transmission must be repeated 3 times as specified in the protocol. The transmission code does not implement the RC5/6 toggle bit; that is up to the caller.

Adding new protocols

Manufacturers have implemented many more protocols than this library supports. Adding new protocols should be straightforward if you look at the existing library code. A few tips: It will be easier to work with a description of the protocol rather than trying to entirely reverse-engineer the protocol. The durations you receive are likely to be longer for marks and shorter for spaces than the protocol suggests. It's easy to be off-by-one with the last bit; the last space may be implicit.