Help translate this public domain Mpeg Layer 1 decoder to Lazarus

[domasz]

I found a public domain Mpeg Layer 1 decoder written in C++ and started porting it to Pascal. But the thing is- I barely know C++.

Could anybody help so Pascal has a native Mpeg Layer 1 decoder?

Source CPP (because it can't be attached):
https://www.jonolick.com/uploads/7/9/2/1/7921194/jo_mp1.cpp

Sample file:
https://samples.ffmpeg.org/A-codecs/mp1-sample.mp1

Usage example:

Code: [Select]

procedure TForm1.Button1Click(Sender: TObject);
var F: TFileStream;
    Buf1: array of Byte;
    Buf2: array of CShort;
    Len1,Len2: Integer;
    Hz, Channels: Integer;
    res: cbool;
begin
  F := TFileStream.Create('test.mpeg', fmOpenRead or fmShareDenyWrite);
  Len1 := F.Size;
  SetLength(Buf1, Len1);
  F.Read(Buf1[0], Len1);
  F.Free;


  res := jo_read_mp1(@Buf1,
              Len1,
              @Buf2,
              Len2,
              Hz,
              Channels);

  if res then
    showMessage(format('%d %d', [hz, channels]))
  else
    showmessage('bad');
end; 


[winni]

Hi!

Not what you are looking for but:

All ways lead to Rome:

https://github.com/TheLazyTomcat/bnd.mpg123/blob/master/mpg123.pas


Winni

[domasz]

Thank you, but that's quite useless as it requires a different DLL every time you want to compile for a different architecture. That's why I want a Pascal native library.

[wp]

There's another mp3 decoder which even is for Lazarus: https://github.com/dpethes/mp3dp. I tested it - it is working. For the mp3player_demo you do need external dlls (sdl2.dll and cimgui.dll) - but this is independent of the mp3 decoding process; there is another demo, mp3_decode, which runs on its own, without a dll.

[Zvoni]

Just looked at his code:
What in blazes is a "Pointeger"? Should be "Pointer"

EDIT: And there are some other things wrong in his argument-lists
in jo_read_mp1
"OutPut" is a Reference to a pointer to Short (That's an Int16, right?), so at a guess it should be "var OutPut:PInt16" or something

in jo_readBits
first argument should be "const data:PByte"

and nevermind that when porting C/C++-code you should use the CTypes-Unit with its C-types provided

[domasz]

There's another mp3 decoder which even is for Lazarus: https://github.com/dpethes/mp3dp. I tested it - it is working.

This is based on Delphi MPEG which is GNU/GPL and Delphi MPEG is based on maplay which is also GNU/GPL. So this thing is GNU/GPL.

[domasz]

Just looked at his code:
What in blazes is a "Pointeger"? Should be "Pointer"

EDIT: And there are some other things wrong in his argument-lists
in jo_read_mp1
"OutPut" is a Reference to a pointer to Short (That's an Int16, right?), so at a guess it should be "var OutPut:PInt16" or something

in jo_readBits
first argument should be "const data:PByte"

and nevermind that when porting C/C++-code you should use the CTypes-Unit with its C-types provided

Thank you very much! Very useful! I updated the file in the first post.

Can you tell me how to translate this?

Code: [Select]

output = (short*)realloc(output, outputMax);

[korba812]

Can you tell me how to translate this?

Code: [Select]

output = (short*)realloc(output, outputMax);

https://www.freepascal.org/docs-html/rtl/system/reallocmem.html

Code: Pascal  [Select][+][-]

1. output := ReAllocMem(output, outputMax);

[domasz]

Can you tell me how to translate this?

Code: [Select]

output = (short*)realloc(output, outputMax);

https://www.freepascal.org/docs-html/rtl/system/reallocmem.html

Code: Pascal  [Select][+][-]

1. output := ReAllocMem(output, outputMax);

Thank you. It compiles now but doesn't seem to work. Most likely I made an error in translation

[dpethes]

You do realize that this is a layer 1 decoder and as such of extremely limited use (I haven't seen a layer 1 file pretty much ever)? I'm pointing this out because you renamed it to jo_mp3 , and this is misleading and far from an actual mp3 decoder, like mp3dp.

[domasz]

Yes, I thought it was MPEG 1 Layer 3 but it's just Layer 1.

If your mp3dp had a usable license it would be an amazing thing.

[serbod]

I can translate, it's not very big and complicated. If it still actual.

Also, I translated public domain MP3 decoder with permissive MIT license:

https://github.com/serbod/acs/blob/master/src/formats/general/mp3.pas

But it has flaws in L3_Subband_Synthesis() procedure, and I can't properly debug it step-by-step because known working algorithm from mp3dp (see comments above) is totally different.

UPD: Flaws was fixed, and usage example added.

[domasz]

I can translate, it's not very big and complicated. If it still actual.

Also, I translated public domain MP3 decoder with permissive MIT license:

You did a great job with the MP3 decoder, Sergey! Much appreciated!
I didn't find any MPEG-1 Layer 1 decoder in Pascal and my attempt at conversion wasn't  successful. So yes- it is actual.