24/96 flac content

[mehrvarz]

Are 24 bps 96khz flac files supported in general? Has anyone played back such content via mewkiz/flac? With the help of mewkiz/flac and gordonklaus/portaudio I am able to play back standard 16/44.1 flac files (some perfectly / some almost perfectly, see #29 ). However, I'm not yet able to play back 24/96 files in the same way. The problem is most likely in my code. But it could also be an issue in either mewkiz/flac or gordonklaus/portaudio. This is why I would like to ask if anybody has managed to play back 24/96 flac content from their Go app. (I can play back 24/96 flac files via VLC to my USB DAC in bitperfect fashion. Just not via my Go app, yet.) Thank you.

[mewmew]

Hi @mehrvarz!

We just tried playing a FLAC file with 24 bps and 96kHz and it worked without glitches. Would you please try playing your FLAC file with the following snippet:

package main

import (
	"flag"
	"fmt"
	"log"
	"os"
	"time"

	"github.com/faiface/beep"
	"github.com/faiface/beep/flac"
	"github.com/faiface/beep/speaker"
)

func main() {
	flag.Parse()
	if flag.NArg() != 1 {
		fmt.Fprintf(os.Stderr, "Usage: blip FILE\n")
		os.Exit(1)
	}
	fr, err := os.Open(flag.Arg(0))
	if err != nil {
		log.Fatalf("unable to open file; %v", err)
	}
	s, format, err := flac.Decode(fr)
	speaker.Init(format.SampleRate, format.SampleRate.N(time.Second/10))
	done := make(chan struct{})
	f := func() {
		close(done)
	}
	notify := beep.Callback(f)
	speaker.Play(beep.Seq(s, notify))
	select {
	case <-done:
		break
	}
}

Note: github.com/faiface/beep/flac uses github.com/mewkiz/flac under the hood.

[mehrvarz]

Cool. Unfortunately I get...

../gopath/pkg/mod/github.com/hajimehoshi/oto@v0.1.2/player.go:25:18: undefined: player

hajimehoshi/oto is referenced from faiface/beep/speaker.

Before that I tried using mewkiz/flac/cmd/flac2wav to convert some of my 24/96 flac files to wav format. But when I try to play back these wav files via VLC, I get the same scrambled audio noise that I get when I play them back directly via gordonklaus/portaudio.

[mewmew]

Before that I tried using mewkiz/flac/cmd/flac2wav to convert some of my 24/96 flac files to wav format. But when I try to play back these wav files via VLC, I get the same scrambled audio noise that I get when I play them back directly via gordonklaus/portaudio.

Hmm. Would you mind uploading a sample FLAC file that exhibits this issue? Definitely sounds like you uncovered something incorrect in the flac library.

[mehrvarz]

Two sample 24bit flac files:
http://www.lindberg.no/hires/test/2L-125_stereo-88k-24b_04.flac
http://helpguide.sony.net/high-res/sample1/v1/data/Sample_BeeMoved_96kHz24bit.flac.zip

[mewmew]

Cool. Unfortunately I get...

../gopath/pkg/mod/github.com/hajimehoshi/oto@v0.1.2/player.go:25:18: undefined: player

Try running

go get -v -u github.com/mewspring/blip

And use the blip tool to play the FLAC file. Does that work?

[mewmew]

I can confirm that it is lagging with github.com/mesilliac/pulse-simple for the sample you uploaded Sample_BeeMoved_96kHz24bit.flac.

However, playing the sample file Sample_BeeMoved_96kHz24bit.flac with github.com/faiface/beep works perfectly on my laptop without any glitches.

[mewmew]

Oh, and thanks for the uploaded FLAC files!

[mehrvarz]

Yes github.com/mewspring/blip does work well and it seems to be able to play back all my flac content correctly (Edit: see below). I tested several 24/96 files and also some 16/44.1 files with blockSize=5.

mewkiz/flac/cmd/flac2wav still does not work for 24/96 content. Does mewspring/blip depend solely on mewkiz/flac? Or does it work differently?

[mehrvarz]

I just notice that mewspring/blip does not seem to make use of mewkiz/flac. What do I need to do to get the working flac decoder?

[mehrvarz]

So mewspring/blip does make use of mewkiz/flac internally. But I found some essential code in faiface/beep/flac/decode.go in regard to several bps cases. Should this not be part of the decoder package? But still very useful. Thank you for now.

[mehrvarz]

faiface/beep/flac/decode.go seems to be converting 24bit down to 16bit by throwing out bits before playback. A rather simplified solution. Do you agree?

[mewmew]

faiface/beep/flac/decode.go seems to be converting 24bit down to 16bit by throwing out bits before playback. A rather simplified solution. Do you agree?

If that's the case it's definitely a bug and should be fixed. Where did you see the truncation to 16 bit?

As far as I can tell from https://github.com/faiface/beep/blob/master/flac/decode.go#L116 the 24-bit samples are converted to int32 before being converted to a floating-point value.

	case bps == 24 && nchannels >= 2:
		for i := 0; i < n; i++ {
			d.buf[i][0] = float64(int32(frame.Subframes[0].Samples[i])) / (1<<23 - 1)
			d.buf[i][1] = float64(int32(frame.Subframes[1].Samples[i])) / (1<<23 - 1)
		}

[mewmew]

As of rev da5a5e9 go-audio/wav is used instead of the WAV encoder provided by the Azul3D engine. The rationale being that go-audio/wav seem to be maintained and under active development.

Also, with the switch flac2wav is able to convert Sample_BeeMoved_96kHz24bit.flac to a WAV file that plays back perfectly. Please give it a try and report back :)

[mehrvarz]

The code two posts up, is this your code? Do you happen to know what "divide by (1<<23 - 1)" is meant to do? The intent appears to be to divide by 0x800000 (not 0x7fffff). In other words to do: (val >> 24). Aren't bits being thrown out here? Don't you think that doing 24bit should involve some bit packing? As in 4 x 24 = 3 x int32 ?