How to get MP3 file Bitrate ? (Delphi)

Question

how can i get bitrate of a MP3 File ?

What's your mean ? so how can you see the `bitrate` property in the properties dialog of mp3 files in the windows ? — Kermia, Apr 22 '11 at 20:15
Kermia - for VBR (variable bitrate) the best you can do is take the size of the mp3 data stream and divide it by its audio length in seconds, and multiply by 8 (to convert bytes to bits). In other words, it would be an average bitrate. — Barry Kelly, Apr 23 '11 at 00:54

score 5 · Answer 1 · answered Apr 23 '11 at 01:06

MP3 Bitrate is stored in the 3rd byte of frame header so an option would be to search for the first byte with a value 255 (in theory there's should be no other bytes with all bits set to 1 before that) and bitrate should be stored two bytes after that. Following code does this:

program Project1;

{$APPTYPE CONSOLE}

uses
  Classes, SysUtils;

const
  BIT_RATE_TABLE: array [0..15] of Integer =
    (0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 0);

var
  B: Byte;
begin
  with TFileStream.Create(ParamStr(1), fmOpenRead) do begin
    try
      Position := 0;
      repeat
        Read(B, 1);
      until B = 255;
      Position := Position + 1;
      Read(B, 1);
      Writeln(BIT_RATE_TABLE[B shr 4]);
    finally
      Free;
    end;
  end;
end.

Note that this only finds bitrate of the first frame.

You can find more detailed info from here

score 4 · Accepted Answer · answered Apr 23 '11 at 07:23

4

Have a look at TAudioFile.GetMp3Info in Read MP3 info (just ignore the german description)

answered Apr 23 '11 at 07:23

Matthias Alleweldt

2,333
15
16

Thank you so much , That's i wanted exactly. – Kermia Apr 23 '11 at 10:20

score 3 · Answer 3 · answered Apr 23 '11 at 00:41

You'll have to create a Delphi structure to read the MP3 file format.

That format is defined here:

http://en.wikipedia.org/wiki/MP3#File_structure

This link: http://www.3delite.hu/Object%20Pascal%20Developer%20Resources/id3v2library.html

appears to contain Delphi code for reading the format as well.

More basically, every file has a format, and generally you need to create a data structure to map that format. You then use file reading code to map the data in the file on top of structure that defines the file format.

How to get MP3 file Bitrate ? (Delphi)

3 Answers3