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Calculating Parameter Values

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[The feature associated with this page, DirectShow, is a legacy feature. It has been superseded by MediaPlayer, IMFMediaEngine, and Audio/Video Capture in Media Foundation. Those features have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use MediaPlayer, IMFMediaEngine and Audio/Video Capture in Media Foundation instead of DirectShow, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

Potentially, an input buffer could be very large. Ideally, when the DMO processes the buffer, the parameters will exactly follow their curves throughout the entire batch of data. However, a DMO has some leeway in how it calculates those values.

  • The most accurate approach is to calculate the exact value for every atomic unit of data; for example, each audio sample. This approach is the most computationally expensive.
  • Another approach is to slice the data into smaller units of some fixed size, such as 100 samples. This approach creates a "stair-stepping" effect. For some parameters, that might be acceptable. In audio effects, it might create audible artifacts.
  • A compromise is to use the previous technique, but within each batch, perform a linear interpolation of the parameter value for each sample.

These issues are especially important for audio processing. One second of audio might contain 48,000 audio samples per channel, which is a lot of calculations to perform, yet the ear is sensitive to artifacts such as aliasing.

Media Parameters