Resample.hs

module Data.MediaBus.Audio.Resample ( resample8to16kHz' ) where

import           Data.MediaBus.Stream
import           Data.MediaBus.Sample
import           Data.MediaBus.Audio.Raw
import           Conduit
import qualified Data.Vector.Storable         as V
import qualified Data.Vector.Storable.Mutable as M
import           Control.Monad.State.Strict
import           Control.Lens
import           Control.Parallel.Strategies  ( NFData, rdeepseq, using )

resample8to16kHz' :: (NFData s, NFData t, NFData p, NFData i, IsAudioSample sa, GetAudioSampleRate sa ~ 8000, Monad m, IsAudioSample (SetAudioSampleRate sa 16000), NFData (SetAudioSampleRate sa 16000))
                  => sa
                  -> Conduit (Stream i s t p (SampleBuffer sa)) m (Stream i s t p (SampleBuffer (SetAudioSampleRate sa 16000)))
resample8to16kHz' !sa = evalStateC sa (mapPayloadMC' resample)
  where
    resample !sb
        | sampleCount sb == 0 = return (MkSampleBuffer mempty)
        | otherwise = do
              !lastVal <- get
              let !lastVal' = V.last (sb ^. sampleVector)
              put lastVal'
              let !sb' = createSampleBufferFrom (interpolate lastVal) sb
              return sb'
      where
        interpolate !lastVal !vIn = do
            let !lenOut = 2 * lenIn
            !vOut <- M.new lenOut
            void $ lerpSamples vOut (doubleAudioSampleRate lastVal) 0
            return (vOut `using` rdeepseq)
          where
            !lenIn = V.length vIn
            lerpSamples !vOut !prev !i =
                when (i < lenIn) $ do
                    !nextHalfRate <- V.indexM vIn i
                    let !next = doubleAudioSampleRate nextHalfRate
                    let !smpl = avgSamples prev next
                    M.unsafeWrite vOut (2 * i) smpl
                    M.unsafeWrite vOut (2 * i + 1) next
                    lerpSamples vOut next (i + 1)