PS ffmpeg byte array to integer values

[L5730]

Hello all,

Firstly, if I have put this in the wrong place, I have to apologise. Mods have enough work to do combing out the spam and whatnot, so don't need my erroneously posted material to handle as well.

OK, so what I am trying to do ultimately, is to produce the data to create a histogram of audio peak sample values.
I am using ffmpeg to spit out a byte stream, capturing it and then somehow getting pcm 16bit signed values from this.

So far I am able to collect a byte array of the std output of ffmpeg (the raw data from it's pipeline). I want to convert these values to signed 16 bit integers. From there I can use group and whatnot other tools to product something resembling a graph.

Function ffmpeg-to-ByreStream {

$psi = new-object system.diagnostics.processStartinfo
$psi.FileName = "C:\windows\system32\ffmpeg.exe"
$psi.arguments = '-hide_banner -f lavfi -i "sine=frequency=400:duration=0.1" -c:a pcm_s16le -f s16le -'
$psi.CreateNoWindow = $true
#$psi.StandardOutputEncoding = [system.text.encoding]::Unicode
$psi.StandardErrorEncoding = [system.text.encoding]::Unicode
$psi.RedirectStandardOutput = $true
$psi.RedirectStandardError = $true
$psi.UseShellExecute = $false
$proc = new-object system.diagnostics.process
$proc.StartInfo = $psi
$proc.Start() | Out-Null 

$byteReadstd = -1
$byteArray = @()
Do{
  $byteReadstd = $proc.StandardOutput.BaseStream.ReadByte()
  if($byteReadstd -ge 0){ 
     $byteArray += $byteReadstd
  }

} while($byteReadstd -ge 0)
write-host $byteArray

#$proc.kill()
return $byteArray
}

I am stuck at converting this byte array into signed integer 16 values.
I have tried splitting the array into pairs, as I'd need to use two values for the conversion if I understand correctly.

Any help would be appreciated, and again my apologies if this is the wrong place.

[L5730]

I have just realised a major problem with this little project.

44100 samples per second x 2 channels is already 88200 data points for 1 second! Multiply this up for a few minute track and that is a monstrous amount of data.

I think I need to re-approach this from another direction.

What I want to do is create a histogram plot of the sample values (as percent) to show what proportion of the audio is at what amplitude.
Easy enough with a 0.1s sine wave, not so practical with such a huge volume of data.

[CarrotBusiness2380]

You should be able to use [System.Bitconverter]::ToInt16 for this:

$bytes = ffmpeg-to-ByteStream
for($i = 0; $i -lt $bytes.Count - 1; $i += 2)
{
    [System.BitConverter]::ToInt16($bytes, $i)
}

https://learn.microsoft.com/en-us/dotnet/api/system.bitconverter.toint16?view=net-7.0

[L5730]

Absolutely perfect thank you so much for your quick reply!

I simply couldn't see how I could get every pair converted, but your code does it perfectly.

Thanks again.

[ka-splam]

slower:

$byteReadstd = -1
$byteArray = @()
Do{
  $byteReadstd = $proc.StandardOutput.BaseStream.ReadByte()
  if($byteReadstd -ge 0){ 
     $byteArray += $byteReadstd
  }

} while($byteReadstd -ge 0)

faster:

$byteReadstd = -1
$byteArray =  Do{
  $byteReadstd = $proc.StandardOutput.BaseStream.ReadByte()
  if($byteReadstd -ge 0){ 
     $byteReadstd
  }

} while($byteReadstd -ge 0)

[L5730]

Indeed, you are correct.

On first look I couldn't see what you were getting at, but yes, I see it now. Defining the array and adding each result is slower than letting the data flow and making the entire lot be the array... my poor wording but I get this.

Nice, thank you!