For audio capabilities, IAMStreamConfig::GetStreamCaps returns an array of pairs of AM_MEDIA_TYPE and AUDIO_STREAM_CONFIG_CAPS structures. As with video, you can use this to expose all kinds of audio capabilities on the pin, such as data rate and whether it supports mono or stereo.
For video-related examples relating to GetStreamCaps, see Video Capabilities.
Suppose you support pulse code modulation (PCM) wave format (as represented by the WAVEFORMATEX structure) at sampling rates of 11,025, 22,050, and 44,100 samples per second, all at 8- or 16-bit mono or stereo. In this case, you would offer two pairs of structures. The first pair would have an AUDIO_STREAM_CONFIG_CAPS capability structure saying you support a minimum of 11,025 to a maximum of 22,050 samples per second with a granularity of 11,025 samples per second (granularity is the difference between supported values); an 8-bit minimum to a 16-bit maximum bits per sample with a granularity of 8 bits per sample; and one-channel minimum and two-channel maximum. The first pair's media type would be your default PCM format in that range, perhaps 22 kilohertz (kHz), 16-bit stereo. Your second pair would be a capability showing 44,100 for both minimum and maximum samples per second; 8-bit (minimum) and 16-bit (maximum) bits per sample, with a granularity of 8 bits per sample; and one-channel minimum and two-channel maximum. The media type would be your default 44 kHz format, perhaps 44 kHz 16-bit stereo.
If you support non-PCM wave formats, the media type returned by this method can show which non-PCM formats you support (with a default sample rate, bit rate, and channels) and the capabilities structure accompanying that media type can describe which other sample rates, bit rates, and channels you support.