[Resolved] Help deciphering document

Bah__Name

I've got a file containing supposedly everything I need to know about Wav file formats, but I need help deciphering it.

See attached. I want to record a simple short wav file in sndrec32.exe (windows) then dissect it accurately.

Can anyone help?

piersk

I'm gonna move this to the Echo lounge since I think this is more of a genreral thing rather than a PHP thing.

Bunkermaster

your file is a compressed file containing a wave.html file which holds wav audio format specification...

Bah__Name

I know. What it doesn't say (or maybe it does but I can't see it) is how I take a given wav file and fread() the data chunk. I want to know what arguments to pass to fread() etc, or a substr() of the wav file (or something), and pass the function the start char and length to read, so I have pulled out just the data.

I see the function specs or data types explained in the document, but I still don't see how I tell where the format chunk and data chunks start and end. If I can do that, I can extract the pure data (minus the crap, if any), maybe even concatenate two of these things into one file.. the ultimate dream, and my current PHP challenge. Its just, you know, hard.

😐

bad76

Hi,
you can

1) read all (large usage of server memory) with $data=fread ($fd, filesize ($filename));
2) read byte to byte in a loop with $data=fread ($fd, 1);
3) do a buffered read with $data=fread ($fd, 1024);

Anyway you do this in a function that return the requested byte:

function getwavevalue(x)
{
// do some policy of load
// es: if(!isset($data)) $data=fread ($fd, filesize ($filename));
return $data{x};
}

When you can acces to byte find first occourrence of 'data' string. The next 4 byte is checkID, next 4 is the length of data. From here output this number of byte...

see you

Bunkermaster

awwww thought you couldn't open the file... was at work (tired)

Bah__Name

Thanks.

When you can acces to byte find first occourrence of 'data'>string. The next 4 byte is checkID, next 4 is the length of data.>From here output this number of byte...

🙁 I don't know what the data string should look like. I assume once I know that, everything I need is some kind of offset from there. If it is simply from byte 1, this would be great.

I could (theoretically) write a function to strip out substr()'s (or subByte's equivalent), glue them together and see if they are recognised as a wav file, but I have a feeling I would never, ever succeed this way.

I know I ought to see what I need in the document but aww hell.🙁

Bah__Name

Aha! got it. I am finding the data flag but the Chunksize 4-bytes are asci gobbledegook. I am expecting a number so I can output it as an argument to another function..

<?php
echo GetLength("MyWav.wav") //This returns asci gook..?

function GetLength($wav){
$fp = fopen($wav, 'r');
$i = 0;
while ($Data != 'data' && !feof($fp)){
 fseek($fp, $i);
 $Data = fread($fp, 4);
 ++$i;
}
if( $Data == 'data'){
 print "Yes!<BR>";
 $i+=3;
 fseek($fp, $i);
 $length = fread($fp,1);
 return $length;
}else{
 print "No!<BR>";
 return 0;
}fclose($fp);}
?>

Bah__Name

Aha! got it. I am finding the data flag but the Chunksize 4-bytes are asci gobbledegook. I am expecting a number so I can output it as an argument to another function..

<?php
echo GetLength("MyWav.wav") //This returns asci gook..?

function GetLength($wav){
$fp = fopen($wav, 'r');
$i = 0;
while ($Data != 'data' && !feof($fp)){
 fseek($fp, $i);
 $Data = fread($fp, 4);
 ++$i;
}
if( $Data == 'data'){
 print "Yes!<BR>";
 $i+=3;
 fseek($fp, $i);
 $length = fread($fp,4);
 return $length;
}else{
 print "No!<BR>";
 return 0;
}fclose($fp);}
?>

bad76

Well done !!!

You need just a little correction.

Look this:

function GetLength($wav)
{
	$fp = fopen($wav, 'r');
	$i = 0; $Data="";
	while ($Data != 'data' && !feof($fp))
	{
		 fseek($fp, $i);
		 $Data = fread($fp, 4);
		 ++$i;
	}
	if( $Data == 'data'){
		 print "Yes!<BR>";
		 //$i+=3; //fseek($fp, $i); // a look at dump of wave tell me that
		 							// there are not 4 byte of checkID here...
		 $bing1=ord(fread($fp,1));	// now we have to convert the byte in a long,
		 $bing2=ord(fread($fp,1));  // the php do not this. Be care, the number is reversed
		 $bing3=ord(fread($fp,1));  // on intel machine xxyyzzww -> wwzzyyxx...
		 $bing4=ord(fread($fp,1));
		 return ($bing4*256+$bing3)*256+$bing2*256+$bing1;

}else{
	 print "No!<BR>";
	 return 0;
}
fclose($fp);
}

echo GetLength("MyWav.wav");

On my localhost work fine, so.. good luck.

see you

Weedpacket

Using [man]unpack[/man] may help streamline code for turning raw binary into PHP data types.

bad76

Yes, this work too...

if( $Data == 'data'){
          print "Yes!<BR>";
          $bing1=unpack("L",fread($fp,4));
          return $bing1[""];
}else

Thanks for hint. Now i have to convert some my old routine 😃

see you

Bah__Name

Whoa, coming thick and fast. I'll have a look at this new one.

Meantime, the current example works a treat. I can concatenate several data chunks now
Riff +
fmt +
data +
chunksize1 +
(chunksize2-8) +
(chunksize3-8), however this:

return ($bing4256+$bing3)256+$bing2*256+$bing1;

is fairly complicated.

Do you know how I can sum multiple Chunksizes and convert them back into the correct byte entry?

That is my final hurdle 🙂

Incidentally, how much harder is it to combine data chunks
instead of just concatenating them?

bad76

Hi,
to convert them back into the correct byte entry you can use pack() function. Look php manual for that, it's easy.

To combine data chunks instead of just concatenating them, you can try to just add any value, byte to byte:

$newval=ord($chunk1{1})+ord($chunk2{1});
if ($newval>128) $newval=128;
if ($newval<-128) $newval=-128;

but is not like a poliphone sound.

You can also try to mix with sound recorder of window and look to result:

start with wav1 & wav2, same length. Mix and get wav3.
Then with your script put some result on screen:

wav1 | wav2 | wav3
10 | 110 | 120
100 | -20 | 80
....

if the result is like that it's just an add and you are lucky 😃...

see you