av/exp/pcm/stereo-to-mono/stereo-to-mono.go

/*
NAME
  stereo-to-mono.go

DESCRIPTION
  stereo-to-mono.go is a program for converting a mono pcm file to a stereo pcm file.

AUTHOR
  Trek Hopton <trek@ausocean.org>

LICENSE
  stereo-to-mono.go is Copyright (C) 2018 the Australian Ocean Lab (AusOcean)

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  for more details.

  You should have received a copy of the GNU General Public License in gpl.txt.
  If not, see [GNU licenses](http://www.gnu.org/licenses).
*/
package main

import (
	"flag"
	"fmt"
	"io/ioutil"
	"log"

	"bitbucket.org/ausocean/av/audio/pcm"
	"github.com/yobert/alsa"
)

// This program accepts an input pcm file and outputs a resampled pcm file.
// Input and output file names, to and from sample rates, channels and sample format can be specified as arguments.
func main() {
	var inPath = *flag.String("in", "data.pcm", "file path of input data")
	var outPath = *flag.String("out", "mono.pcm", "file path of output")
	var sf = *flag.String("sf", "S16_LE", "sample format of input audio, eg. S16_LE")
	flag.Parse()

	// Read pcm.
	inPcm, err := ioutil.ReadFile(inPath)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println("Read", len(inPcm), "bytes from file", inPath)

	var sampleFormat alsa.FormatType
	switch sf {
	case "S32_LE":
		sampleFormat = alsa.S32_LE
	case "S16_LE":
		sampleFormat = alsa.S16_LE
	default:
		log.Fatalf("Unhandled ALSA format: %v", sf)
	}

	format := alsa.BufferFormat{
		Channels:     2,
		SampleFormat: sampleFormat,
	}

	buf := alsa.Buffer{
		Format: format,
		Data:   inPcm,
	}

	// Convert audio.
	mono, err := pcm.StereoToMono(buf)
	if err != nil {
		log.Fatal(err)
	}

	// Save mono to file.
	err = ioutil.WriteFile(outPath, mono, 0644)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println("Encoded and wrote", len(mono), "bytes to file", outPath)
}