VGM import doesn't determine start of data correctly

[OPNA2608]

The VGM data stream is currently hardcoded to be expected at 0x100:

YM2608-Tone-Editor/src/io/vgm_io.cpp

Lines 25 to 27 in 0a076ea

	size_t csr = 0x100;
	for (bool flag = true; flag;) {
	switch (uint8_t com = container.readUint8(csr++)) {

This is a bad assumption. The VGM specification says:

So the correct flow for getting the start of the data should be (excluding read checks):

uint32_t version = container.readUint32(0x08);
size_t csr = 0x40;

if (version >= 0x150)
    csr += container.readUint32(0x34);

Some examples of VGM files that don't get read correctly:

YU-NO: Imperial City
VGM version is 0x170, VGM data offset is 0xAC. Real start of VGM data is at 0xE0.
A YM2608 port 0 write (command 0x56) starts at 0xFE, 0x100 has the last argument to that command
-> 0x70, which is being interpreted as a 1-sample wait. All the parsing afterwards is likely very wrong.

Briganty: Coda "BRIGANTY" (Ending)
VGM version is 0x170, VGM data offset is 0xAC. Real start of VGM data is at 0xE0.
A YM2608 port 0 write (command 0x56) starts at 0xFE, 0x100 has the last argument to that command
-> 0x00, which causes the VGM parser to abort due to an unknown command

[rerrahkr]

Thank you for your report. VGM Data Offset is the number of bytes from 0x34, so I will fix this as:

diff --git a/src/io/vgm_io.cpp b/src/io/vgm_io.cpp
index 0667a59..980adfd 100644
--- a/src/io/vgm_io.cpp
+++ b/src/io/vgm_io.cpp
@@ -11,7 +11,7 @@ VgmIo::VgmIo() : AbstractSongFileIo("vgm", "VGM file") {}
 
 std::vector<TonePtr> VgmIo::load(BinaryContainer& container) const
 {
-    if (container.size() < 256) throw FileCorruptionError(io::FileType::SongFile);
+	if (container.size() < 0x40) throw FileCorruptionError(io::FileType::SongFile);
 
     std::string ident = container.readString(0, 4);
     if (ident != "Vgm ") throw FileCorruptionError(io::FileType::SongFile);
@@ -20,9 +20,12 @@ std::vector<TonePtr> VgmIo::load(BinaryContainer& container) const
     uint32_t eof = container.readUint32(4);
     if (container.size() - 4 != eof) throw FileCorruptionError(io::FileType::SongFile);
 
+	uint32_t version = container.readUint32(0x08);
+	size_t csr = (version < 0x150) ? 0x40 : (0x34 + container.readUint32(0x34));
+	if (container.size() <= csr) throw FileCorruptionError(io::FileType::SongFile);
+
 	RegisterRecorder rec(44100);
 
-    size_t csr = 0x100;
 	for (bool flag = true; flag;) {
 		switch (uint8_t com = container.readUint8(csr++)) {
 		case 0x52:	// YM2612 Port A

[rerrahkr]

I fixed this in ee95aad.