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kVTDecompressionPropertyKey_ReducedFrameDelivery

The proportion of frames that should be delivered, indicating that the rest may be dropped.

Declaration

let kVTDecompressionPropertyKey_ReducedFrameDelivery: CFString

Discussion

This is an optional property for video decoders to implement. If supported, it requests that frame delivery be reduced by the specified amount.

This number is a fraction between 0.0 and 1.0 that indicates what proportion of frames should be delivered–others may be dropped. For example, 0.25 would indicate that only one frame in every four should be delivered. This is a guideline; the actual selection of frames is up to the decoder, which knows which frames can be skipped without harm.

You can use this key on its own, or in the dictionaries returned in the array obtained from kVTDecompressionPropertyKey_SuggestedQualityOfServiceTiers. This key may also be used in conjunction with kVTDecompressionPropertyKey_OnlyTheseFrames. For example, the dictionary containing [{kVTDecompressionPropertyKey_OnlyTheseFrames, kVTDecompressionProperty_OnlyTheseFrames_KeyFrames}, {kVTDecompressionPropertyKey_ReducedFrameDelivery, 0.25}] requests that the decoder only deliver a quarter of keyframes.

If the decoder does not support this property directly, but reports that the content has no interframe dependencies, VideoToolbox may step in and perform simple frame dropping.

See Also

Decoder Behavior