AV Foundation wastes energy processing Audio even if not captured

Number:rdar://16389364 Date Originated:21 march 2014
Status:Open Resolved:
Product:iOS SDK Product Version:iOS 7.1 (11D167)
Classification:Performance Reproducible:Always
Apps which have no interest in capturing audio still incur energy waste for processing audio.

In my usage scenario (see sample) I am connecting the back-facing camera with a capture session and a metadata detector output for scanning barcodes. I have no interest in audio. Yet, in the Energy Diagnostics Instrument the "Audio Processing"  bars hover around 20%.

From this I infer that Audio Processing is occurring even though it wouldn't have to. There does not appear any way for a developer to indicate to iOS that audio should be ignored.

Steps to Reproduce:
1. Open the provided sample app in Xcode
2. Profile it with the "Energy Diagnostics" Instrument

Expected Results:
The Audio Processing (blue) portion of CPU Activity should be near 0%.

Actual Results:
Audio Processing is around 20% on an iPhone 5S.

iOS 7.1 (11D167)

Please give information if this is intended behavior. Would it be a good enhancement to request to be able to instruct AV Foundation to ignore audio for barcode scanning scenarios like this?


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