Roman Scherbakov (V_Soft) is designer of this file format.
This is the best format for storing interrupted music from different AY-3-8910/12
and YM2149 based platforms.


Offset	Size	Type	Description

00	2	Word	VTX file identifier (ay or ym)
			Its chip type by default:
			this is 7961h or 31073 dec (ay)
			this is 6D79h èëè 28025 dec (ym)
02	1		Byte bit		Playing mode by default:
			Bits 0–2 determine stereo mode:
			0 – MONO, 1 – ABC, 2 – ACB, 3 – BAC,
			4 – BCA, 5 – CAB, 6 – CBA (dec)
03	2	Word	Loop VBL number (from zero =
			beginning of melody).

05	4	Dword	AY chip frequency for this melody
			( for compatibility with non-Spectrum platforms)
			Standard values:
			ZX_Spectrum: 1773400 (or 001B0F58h)
			Atari: 2000000 (or 001E8480h)
			Amstrad CPC: 1000000 (or 000F4240h)
09	1	Byte	Player frequency (VBL per sec).
			Standard value 50 =
			1/50 sec (20ms).
10	2	Word	Year of composition creating.
12	4	Dword	Size of not packed data.
			Needed for unpacking.
16	1..255	str	melody name
??	1..255	str	author name
??	1..255	str	Melody source program name
??	1..255	str	Musical editor name
??	1..255	str	Comment
??	??	data	lha5-compressed data


Remarks.

1) Data compressed with LHA type 5. May to pack with LHA.EXE
   (as YM files), but needed to cut header and last zero byte of compressed file.
   Header of LHA-archive file is found at start of file.
   Its length is value of first byte of header plus 2.

2) After unpacking the data block is equivalent to YM3 data block.

3) Type str in the upper table is 1...254 chars, must be ended with zero.

VTX files can be converted from emulators sound dump files
(for ZX Spectrum and MSX this is usually PSG-files).
But last time you can find emulators, which can to dump music in VTX format too.
One of them is Unreal Speccy by SMT.