Libav
filter_audio.c

This example will generate a sine wave audio, pass it through a simple filter chain, and then compute the MD5 checksum of the output data.The filter chain it uses is: (input) -> abuffer -> volume -> aformat -> abuffersink -> (output)

abuffer: This provides the endpoint where you can feed the decoded samples. volume: In this example we hardcode it to 0.90. aformat: This converts the samples to the samplefreq, channel layout, and sample format required by the audio device. abuffersink: This provides the endpoint where you can read the samples after they have passed through the filter chain.