silence.hs

module Silence (silence, silentStream, silentFile) where

import Data.ByteString.Builder
import Data.Int (Int64)
import Data.Monoid ((<>))

import qualified Data.ByteString.Lazy as BL

type Seconds = Int64

header :: Builder
header = word8 0xFF <>
         word8 0xFB <>
         word8 0x91 <>
         word8 0x04

silent :: Builder
silent = lazyByteString $ BL.take 413 $ BL.repeat 0x0

frames :: Builder
frames = foldr1 (<>) (repeat frame)
  where frame = header <> silent

silence :: Seconds -> BL.ByteString
silence nSec = BL.take (nSec * fps * fLen) silentStream
  where fLen  = 417
        fps = 38

silentStream :: BL.ByteString
silentStream = toLazyByteString frames

silentFile :: FilePath -> Seconds -> IO ()
silentFile path seconds = BL.writeFile path $ silence seconds