C++ Pointer PCM Data Access FMOD Sound Lock

BlitzMax Forums/BlitzMax Programming/C++ Pointer PCM Data Access FMOD Sound Lock

tesuji

(Posted 2012) [#1]

Hi,

I would like to be able to speedily generate a visual representation of entire waveforms based on raw PCM data using the FMOD audio lib (via BaH.FMOD). Getting a bit stuck on how to access the PCM data after a call out to C. Any help would be appreciated.

The FMOD API docs says that the Sound Lock method is best suited for that purpose but alas, it doesn't appear to be present in the bmax wrapper so I've attempted to add it myself. The sound lock definition appeared to be present in the C header files for the FMOD lib. I seem to be most of the way there to hooking it up but I'm having a problem getting visibility of the PCM data in Blitzmax. This may be exacerbated by my lack of experience with C++ ;-)

Anyhow, here's what I've got so far. The sound lock call appears to work in that it returns the correct length vars but as soon as I try and access the byte ptr from bmax it blows up with a memory access violation. Accessing the pointers from C++ works so I suspect it's something to do with how the pointer is being passed back or used in bmax land (this is on a Mac BTW, although shouldn't be too different on Windows).

sound_lock_test.bmx

SuperStrict

Framework BaH.FMOD
Import BRL.GLMax2d
Import BRL.StandardIO

Local system:TFMODSystem = New TFMODSystem.Create()

system.Init(32)

Local sound1:TFMODSound = system.CreateSoundURL("test.mp3", FMOD_SOFTWARE)
sound1.SetMode(FMOD_LOOP_OFF)

Local sampleLength:Int
sound1.GetLength(sampleLength, FMOD_TIMEUNIT_PCM)
Print "Sample loaded.. bytes: "+sampleLength

Local pcmData1:Byte Ptr
Local pcmData2:Byte Ptr
Local len1:Int
Local len2:Int 
Local result:Int = sound1.Lock(0,sampleLength, pcmData1, pcmData2, len1,len2)
Print "result code "+result
Print "fetched length "+len1

' iterate through each byte of PCM data - blows up trying to access wrong memory location
For Local i:Int = 0 To len1-1
	Print pcmData1[i]
Next

End

Modifications to BaH.FMOD

fmod.bmx - additional method in Type TFMODSound

	Method Lock:Int( offset:Int, length:Int, ptr1:Byte Ptr, ptr2:Byte Ptr, len1:Int Var, len2:Int Var )
		Local result:Int = bmx_FMOD_Sound_Lock(soundPtr, offset, length, ptr1, ptr2, len1, len2)
		Return result 
	End Method

common.bmx - C function declaration in Externs

	Function bmx_FMOD_Sound_Lock:Int(handle:Byte Ptr, offset:Int, length:Int, p1:Byte Ptr, p2:Byte Ptr, l1:Int Var, l2:Int Var)

glue.cpp - additional C wrapper function

extern "C" {
	FMOD_RESULT bmx_FMOD_Sound_Lock(FMOD_SOUND * sound, unsigned int offset, unsigned int length, void *ptr1, void *ptr2, unsigned int *len1, unsigned int *len2);

..

}

FMOD_RESULT bmx_FMOD_Sound_Lock(FMOD_SOUND * sound, unsigned int offset, unsigned int length, void *ptr1, void *ptr2, unsigned int *len1, unsigned int *len2) {
	FMOD_RESULT result =  FMOD_Sound_Lock(sound, offset, length, &ptr1, &ptr2, len1, len2 );	
	return result;
}

The FMOD API docs define sound lock like this :

Sound::lock

Returns a pointer to the beginning of the sample data for a sound.

C++ Syntax

FMOD_RESULT Sound::lock(
unsigned int offset,
unsigned int length,
void ** ptr1,
void ** ptr2,
unsigned int * len1,
unsigned int * len2
);

Parameters

offset
Offset in bytes to the position you want to lock in the sample buffer.

length
Number of bytes you want to lock in the sample buffer.

ptr1
Address of a pointer that will point to the first part of the locked data.

ptr2
Address of a pointer that will point to the second part of the locked data. This will be null if the data locked hasn't wrapped at the end of the buffer.

len1
Length of data in bytes that was locked for ptr1

len2
Length of data in bytes that was locked for ptr2. This will be 0 if the data locked hasn't wrapped at the end of the buffer.

Return Values

If the function succeeds then the return value is FMOD_OK.
If the function fails then the return value will be one of the values defined in the FMOD_RESULT enumeration.

Remarks

You must always unlock the data again after you have finished with it, using Sound::unlock.
With this function you get access to the RAW audio data, for example 8, 16, 24 or 32bit PCM data, mono or stereo data, and on consoles, vag, xadpcm or gcadpcm compressed data. You must take this into consideration when processing the data within the pointer.

Last edited 2012