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Warning: this text is still just a draft and mostly used by myself

Research into reverse engineering FL Studio's .fnv file format

What is fnv?

.fnv (most likely standing for 'fruity envelope') - is a proprietary file format for saving curves, envelopes, graphs and other connected point content (also called states) inside FL Studio. Here are some examples of curves you might have encountered in FL:

envelope

lfo

graph

automation_clip

Apart from being just the examples, these are actually the only types of curves to exist in FL, they are:

  • Envelope

  • LFO Envelope

  • Graph

  • EQ (Old name: Map) - quite rare, so far only found in Edison's EQ and Denoise tools. Mostly identical to Graph.

  • Automation clips.*

    * - automation clips can't actually be saved in fnv files directly, but their states can be copied and pasted inside FL. More on that later

All of them have their disctinctive features and are saved in .fnv's differently. I analyze them using a hex editor, so expect a lot of byte values and adresses. First of all, let's look at what is the same for all types:

The Similarities:

  1. Contents of curves

    Each curve is made of points, which are connected with each other by connections(?). These connections can be modified and customised by changing their modes and their tensions. Connections cannot overlap vertically, however instant jumps, where 2 or more points have same x coordinates are allowed.

  2. Point modes

    There are a number of ways you can connect 2 points inside the curves. These ways will are called modes. Here's a list of them in FL:

    modes

    And in text:

    Name Short* Byte
    Hold HD 02
    Smooth SM 0A
    Single Curve SC 00
    Single Curve 2 SC2 07
    Single Curve 3 SC3 0B
    Double Curve DC 01
    Double Curve 2 DC2 01
    Double Curve 3 DC3 08
    Half Sine HS 09
    Stairs ST 03
    Smooth Stairs SST 04
    Pulse PU 05
    Wave WV 06

    *short names are unofficial

    As you can see, the bytes aren't in the correct order. Here's a different version of this table, sorted by byte.

    Byte Name Short
    00 Single Curve SC
    01 Double Curve DC
    02 Hold HD
    03 Stairs ST
    04 Smooth Stairs SST
    05 Pulse PU
    06 Wave WV
    07 Single Curve 2 SC2
    08 Double Curve 2 DC2
    09 Half Sine HS
    0A Smooth SM
    0B Single Curve 3 SC3
    0С Double Curve 3 DC3

    (this might be the order in which the modes were implemented!)

    Modes specify how a connection should be built from the left side of a point (connecting the current one and the previous one, not the next)

  3. Common FNV file structure facts

    *(This section is highly likely to be changed and will be edited a lot)

    • 1st byte defines the curve type
    • Points are saved in chunks of 24 bytes, (6 DWORDs?) which makes it possible to get the number of points in a FNV using only the fnv file size
    • The 0x8th-0xBth bytes represent the number of points in a curve (in little endian)
    • The x coordinates of points are not absolute, but are relative to the previous point (the x coordinate in the FNV itself stores an offset, rather than a coordinate). This prevents the connections from overlapping
    • The maximum number of points is the unsinged 32 bit integer limit, being 4294967295
    • The last 32 bytes (the "footer") define global settings, such as being on/off, lfo phase
    • ‼️New discovery: i have reverse engineered 3 out of 4 bytes that make up a y coordinate: given a floating point number or the coordinate, convert it to its binary representation, bitshift to the right by 3 bits, and reverse the last three digits. whilst the first byte didn't work out, the other three will match the one that is in an fnv point representation.

The Differences:

Envelope

envelope

First byte in header: 01

Minimum number of points: 1

Number of points formula:
N = (F-72)/24+1, where N - number of points, F - file size in bytes

In the footer, the first 4 bytes are FF FF FF FF (they might be a separator, however, as we may see now, they can also represent global values). By default, the next 3 DWORDs are all FF, however, they actually specify which points have the ADSR section flags. First DWORD is for Decay, second is for Loop start, and the third is for Sustain / Loop end (the list matches the order of the options in FL). Each chuck is just an index of a point that has these values turned on, and if none do, it goes to the default value (4 FF bytes)

LFO Envelope

chunk Minimum number of points: 1

First byte in header: 02
Byte -28: tempo/global flags:

Byte Tempo Global
00 Off Off
01 On Off
02 Off On
03 On On

Bytes -4:-1: LFO phase shift

Number of points formula:
N = (F-76)/24, where N - number of points, F - file size in bytes

Byte Frozen Bipolar
07 Off Off
0F On Off
03 Off On
0B On On

Graph

First byte in header: 03

Minimum number of points: 2

Number of points formula:
N = (F-80)/24+2, where N - number of points, F - file size in bytes

Num Byte Diff
1 B0 -
2 C0 16
3 C8 8
4 D0 8
5 D4 4
6 D8 4
7 DC 4
8 E0 4
10 E2 2
11 E4 2
12 E8 2
13 EA 2
14 EC 2
15 EE 2
16 F0 1

EQ (Old name: Map)

First byte in header: 07

Minimum number of points: 2

Basically identical to Graph, but (apparently) it inherently supports shifting the EQ between Log and Linear scale. Still unsure which one of them is actually saved to the file and how the point offsets are represented.