Hi, a while ago I expressed interest in writing tools to help with .spc music. Well, the first step on that journey is a little program I'm working on called "FlarfBrr".

FlarfBrr is essentially going to be a graphical version of Optiroc's Brr encoder program. The user would drag and drop a wav file into the window, have its loop points automatically read, and then have a straight conversion to Brr based on the loop points.

I've added the drag and drop functionality, and now I'm working on a script to test detecting the loop points. After researching the .wav filetype here's what I've come up with in godot

extends Node

# Function to extract and check loop points
func get_loop_points(wav_path: String):
var file = FileAccess.open(wav_path, FileAccess.READ)
if file == null:
print("Error: Could not open file")
return

var buffer = file.get_buffer(file.get_length()) # Read full file
var smpl_bytes = "smpl".to_utf8_buffer() # Convert string to PackedByteArray
var smpl_index = -1

# Manually search for the 'smpl' bytes in the buffer
for i in range(buffer.size() - smpl_bytes.size()):
if buffer.slice(i, i + smpl_bytes.size()) == smpl_bytes:
smpl_index = i
break

if smpl_index == -1:
print("doesn't loop")
return

# Extract loop start and loop end values (little-endian format)
var loop_start_bytes = buffer.slice(smpl_index + 28, smpl_index + 32)
var loop_end_bytes = buffer.slice(smpl_index + 32, smpl_index + 36)

# Reverse manually and decode to uint32
loop_start_bytes.reverse()
loop_end_bytes.reverse()
var loop_start = loop_start_bytes.decode_u32(0) # Decode from the beginning of the slice
var loop_end = loop_end_bytes.decode_u32(0) # Decode from the beginning of the slice

# If loop start and loop end are the same, there's no loop
if loop_start == loop_end:
print("doesn't loop")
return

# If loop points are divisible by 16, it's compatible
if loop_start % 16 == 0 and loop_end % 16 == 0:
print("loopable")
else:
print("incompatible")

# Usage example
func _ready():
get_loop_points("res://OverdriveGuitar.wav") # Change the path to your WAV file

For some reason, samples that loop are incorrectly labeled as non-looping. Can someone help me rewrite this script to properly get the loop points? (I tried posting this on stack overflow but they didn't like it for some reason. jerks)

i think your offsets are wrong - see https://github.com/jangler/osctet/blob/main/src/synth/pcm.rs#L176-L181

Thanks for the quick reply! What language are you using? I need to take a look at the documentation for those methods so I can convert it to godot

(edit) NVM I see it's rust

(edit 2) It works now :D

extends Node

# Function to extract and check loop points
func get_loop_points(wav_path: String):
var file = FileAccess.open(wav_path, FileAccess.READ)
if file == null:
print("Error: Could not open file")
return

var buffer = file.get_buffer(file.get_length()) # Read entire file
var smpl_bytes = "smpl".to_utf8_buffer() # Convert "smpl" to PackedByteArray
var smpl_index = -1

# Find the "smpl" chunk manually
for i in range(buffer.size() - smpl_bytes.size()):
if buffer.slice(i, i + smpl_bytes.size()) == smpl_bytes:
smpl_index = i
break

if smpl_index == -1:
print("doesn't loop")
return

# Read number of sample loops (4 bytes at offset 0x24 from "smpl" start)
var num_loops_offset = smpl_index + 36
if num_loops_offset + 4 > buffer.size():
print("Invalid WAV: smpl chunk too short")
return

var num_loops = _read_little_endian_u32(buffer, num_loops_offset)

if num_loops == 0:
print("doesn't loop")
return

# Read loop points
var all_compatible = true
for i in range(num_loops):
var start_offset = smpl_index + 52 + (i * 28) # 0x34 + (i * 28)
var end_offset = smpl_index + 56 + (i * 28) # 0x38 + (i * 28)

if end_offset + 4 > buffer.size():
print("Invalid WAV: loop point out of range")
return

var start_sample = _read_little_endian_u32(buffer, start_offset)
var end_sample = _read_little_endian_u32(buffer, end_offset)

#idk why but it's always 1 off
end_sample += 1

print("Loop Start:", start_sample, "Loop End:", end_sample)

# Validate loop points
if start_sample == end_sample:
print("Loop points are the same: doesn't loop")
return

if start_sample % 16 != 0 or end_sample % 16 != 0:
all_compatible = false

if all_compatible:
print("loopable")
else:
print("incompatible")


# Helper function to read a little-endian 32-bit unsigned integer
func _read_little_endian_u32(buffer: PackedByteArray, offset: int) -> int:
if offset + 4 > buffer.size():
return 0 # Prevent out-of-bounds reads
var bytes = buffer.slice(offset, offset + 4)
return bytes[0] | (bytes[1] << 8) | (bytes[2] << 16) | (bytes[3] << 24)


# Usage example
func _ready():
get_loop_points("res://bass_elec.wav") # Change the path to your WAV file