encode binary to audio python or C

Question

using C or python (python preferred), How would i encode a binary file to audio that is then outputted though the headphone jack, also how would i decode the audio back to binar

Answer 1

So you want to transmit digital information using audio? Basically you want to implement a MODEM in software (no matter if it is pure software, it's still called modem).

A modem (MOdulator-DEModulator) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data. Modems can be used over any means of transmitting analog signals, from light emitting diodes to radio. [wikipedia]

There are modems everywhere you need to transmit data over an analog media, be it sound, light or radio waves. Your TV remote probably is an infrared modem.

Modems implemented in pure software are called soft-modems. Most soft-modems I see in the wild are using some form of FSK modulation:

Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave.1 The simplest FSK is binary FSK (BFSK). BFSK uses a pair of discrete frequencies to transmit binary (0s and 1s) information.2 With this scheme, the "1" is called the mark frequency and the "0" is called the space frequency. The time domain of an FSK modulated carrier is illustrated in the figures to the right. [wikipedia]

There are very interesting applications for data transmission through atmosphere via sound waves - I guess it is what shopkick uses to verify user presence.

For Python check the GnuRadio project.

For a C library, look at the work of Steve Underwood (but please don't contact him with silly questions). I used his soft-modem to bootstrap a FAX to email gateway for Asterisk (a fax transmission is not much more than a B/W TIFF file encoded in audio for transmission over a phone line).