Vamp Plugin SDK

h1. Output Sample Type and Sample Rate

A Vamp plugin receives audio and produces a series of descriptive feature structures.

The audio input is provided as a series of fixed-length sample blocks, equally spaced in time, provided to successive calls to the plugin's @process@ function. The plugin may return any number of features from each @process@ call, and may also return any number of features from @getRemainingFeatures@ after all the audio has been received.

Features are each associated with a particular output of the plugin. The plugin declares that each output has certain properties, which constrain the sort of feature data the host can expect to see. (See diagram.)

!/attachments/download/980/feature-structures-20pc.png!

A feature may or may not have a timestamp. Whether a timestamp is provided -- and, if it is provided, what it means -- are determined by the @SampleType@ and @SampleRate@ properties of the plugin output on which the feature is returned.

h2. SampleType

A plugin output's @SampleType@ property may be either @OneSamplePerStep@, @FixedSampleRate@, or @VariableSampleRate@. Here's what they mean.

h3. OneSamplePerStep

This is the simplest option. If an output is declared as having a @SampleType@ of @OneSamplePerStep@, then any features returned from a @process@ call are assumed to match up with the audio block provided to that @process@ call.

This means:

 * The plugin should not set the timestamps on any features it returns from a @OneSamplePerStep@ output

 * If the plugin does set timestamps on such features, the host must ignore them

 * The host must treat all features returned from a given @process@ call as if they had the same timestamp as it passed to that @process@ call

 * The host must treat all features returned from @getRemainingFeatures@ as having immediately followed the final @process@ block (i.e. as having the same time as the next equally-spaced @process@ block would have had if the input had not ended).