MoTeC .ld / .ldx Binary File Format Specification

Reverse-engineered from MoTeC i2 Pro telemetry files. Verified against real Oreca 07 LMP2 data. Sufficient to implement a complete parser.

Overview

A MoTeC telemetry session consists of two files:

File	Format	Contents
.ld	Binary, little-endian	Header, channel metadata (linked list), channel sample data
.ldx	XML (UTF-8)	Lap beacon timestamps, session metadata

.ld File Structure

All multi-byte integers are little-endian. Strings are Latin-1 (ISO 8859-1), null-terminated, zero-padded.

File Header (offset 0x00, ~512 bytes)

Offset	Size	Type	Field	Notes
0x00	4	uint32	magic	Always 0x00000040 (64 decimal). Reject file if different.
0x04	4	uint32	reserved	Always 0
0x08	4	uint32	channel_meta_ptr	Byte offset to first channel metadata block
0x0C	4	uint32	channel_data_ptr	Byte offset to start of channel data area
0x10–0x23	20	—	reserved	Zeros
0x24	4	uint32	event_ptr	Byte offset to event info block (0 = none)
0x28–0x5D	54	—	reserved
0x5E	16	string	date	Session date, format "dd/MM/yyyy", e.g. "27/01/2023"
0x6E	16	—	reserved
0x7E	16	string	time	Session start time, format "HH:mm:ss", e.g. "12:00:00"
0x8E	16	—	reserved
0x9E	64	string	driver	Driver name, e.g. "Mikkel Jensen"
0xDE	64	string	vehicle_id	Vehicle identifier, e.g. "MQ12Di_LMP2 #477"
0x11E	64	—	reserved
0x15E	64	string	venue	Track/venue name, e.g. "DIS"

Event Info Block (at event_ptr)

Optional. Only present when event_ptr > 0 and points within the file:

Offset	Size	Type	Field
event_ptr + 0	64	string	event_name

Channel Metadata Block (124 bytes each, linked list)

Channels form a doubly-linked list. Each block is exactly 124 bytes (0x7C).

Start at channel_meta_ptr, follow next_addr until 0 or beyond file end.

Offset	Size	Type	Field	Notes
+0x00	4	uint32	prev_addr	Byte offset to previous channel block (0 for first)
+0x04	4	uint32	next_addr	Byte offset to next channel block (0 for last)
+0x08	4	uint32	data_ptr	Byte offset to this channel's sample data
+0x0C	4	uint32	n_data	Number of samples
+0x10	2	uint16	_id	Internal channel ID (not used for parsing)
+0x12	2	uint16	datatype_a	Data type class (see table below)
+0x14	2	uint16	datatype	Bytes per sample: 2 or 4
+0x16	2	uint16	rec_freq	Recording frequency in Hz
+0x18	2	int16	shift	Integer conversion: additive offset
+0x1A	2	int16	mul	Integer conversion: multiplicative factor
+0x1C	2	int16	scale	Integer conversion: divisor
+0x1E	2	int16	dec_places	Integer conversion: decimal exponent
+0x20	32	string	name	Channel name, e.g. "Corr Speed"
+0x40	12	string	unit	Unit string, e.g. "m/s", "km/h", "bar", "deg", "ratio"
+0x4C	8	string	_short_name	Short name (often empty, not essential)
+0x54	4	uint32	_display_min	Display range minimum (not needed for data)
+0x58	4	uint32	_display_max	Display range maximum
+0x5C	4	float32	_range_max	Physical range maximum (e.g. 200.0 for speed)
+0x60	4	float32	_range_min	Physical range minimum (e.g. 0.0 or -31.1)
+0x64	8	—	reserved
+0x6C	16	—	padding	Zeros to fill 124 bytes

Note: Fields prefixed with _ are informational/display only. Only the fields without _ prefix are required for correct data extraction.

Data Type Classes (datatype_a)

Value	Meaning	Data encoding
0x07	Float	IEEE 754 float. No conversion needed.
0x03	Signed integer	Apply integer-to-physical conversion formula.
Other	Signed integer	Treat same as 0x03.

Channel Data

Located at data_ptr. Contiguous array of n_data samples.

Float data (datatype_a == 0x07)

datatype	Read as	Size
4	IEEE 754 float32 (little-endian)	4 bytes × n_data
2	float16 (rare, fallback to zeros)	2 bytes × n_data

Values are already in physical units — no conversion needed.

Integer data (datatype_a != 0x07)

datatype	Read as	Size
2	Signed int16 (little-endian)	2 bytes × n_data
4	Signed int32 (little-endian)	4 bytes × n_data

Conversion formula (integer → physical value):

scale_eff = (scale == 0) ? 1 : scale
mul_eff   = (mul == 0)   ? 1 : mul

value = (raw / scale_eff * 10^(-dec_places) + shift) * mul_eff

Example: P_F_BRAKE channel with scale=1, dec_places=1, shift=0, mul=1:

• raw int16 value = 423
• value = (423 / 1 × 10⁻¹ + 0) × 1 = 42.3 bar

Linked List Iteration

addr = header.channel_meta_ptr
channels = []
while addr > 0 and addr + 124 <= file_size:
    ch = parse_channel_meta(data, addr)
    channels.append(ch)
    if ch.next_addr == 0 or ch.next_addr <= addr:
        break  # end of list or backward pointer (corrupt)
    addr = ch.next_addr

Safety limit: cap at ~200 channels to protect against corrupt files.

.ldx File Structure

XML file, UTF-8 encoded. Same base filename as the .ld file.

Structure

<?xml version="1.0"?>
<LDXFile>
  <Layers>
    <Layer>
      <MarkerBlock>
        <MarkerGroup>
          <Marker Time="0" />
          <Marker Time="67340000" />
          <Marker Time="135280000" />
        </MarkerGroup>
      </MarkerBlock>
    </Layer>
  </Layers>
</LDXFile>

Parsing

Extract all Time attributes from <Marker> elements using regex or XML parser:

Pattern: <Marker[^>]* Time="(\d+)"

Time Units

Time values are in microseconds (µs). Convert to seconds:

time_seconds = Time / 1_000_000

Lap Computation

Sort beacon times ascending. Each consecutive pair defines a lap:

for i in 0..(beacons.count - 2):
    lap.start = beacons[i]
    lap.end   = beacons[i + 1]
    lap.duration_ms = (lap.end - lap.start) * 1000

Edge cases:

• 0 or 1 beacons: treat entire session as one lap (start=0, end=max_channel_duration)
• .ldx file missing: same fallback

Common Channel Names

Names are case-insensitive for matching. Listed by priority (use first match).

Speed

Name	Typical Freq	Type	Unit
Corr Speed	100 Hz	float32	m/s or km/h
Ground Speed	100 Hz	float32	km/h
Wheel Speed AVG	100 Hz	float32	km/h
Aero Speed	20 Hz	float32	km/h

Throttle

Name	Typical Freq	Type	Unit
Driver Throttle Pos	50 Hz	float32	ratio (0.0–1.0) or % (0–100)
Throttle Pos	50 Hz	float32	ratio or %

Brake

Name	Typical Freq	Type	Unit
P_F_BRAKE	100 Hz	int16	bar (via conversion)
Brake Pos	100 Hz	float32	ratio (0.0–1.0)

Steering

Name	Typical Freq	Type	Unit
Steering Angle	50 Hz	float32	deg (steering wheel degrees)

Gear

Name	Typical Freq	Type	Unit
Gear	10 Hz	float32	integer (0=N, 1–6)

G-Forces

Name	Typical Freq	Type	Unit
G Force Long	50–100 Hz	float32	g

Dampers

Name	Typical Freq	Type	Unit
X_FL_DAMPER	200 Hz	float32	mm
X_FR_DAMPER	200 Hz	float32	mm
X_RL_DAMPER	200 Hz	float32	mm
X_RR_DAMPER	200 Hz	float32	mm

Engine

Name	Typical Freq	Type	Unit
Engine RPM	100 Hz	float32	rpm

Unit Normalization

Speed → km/h

Unit	Factor
m/s	× 3.6
km/h	× 1.0
mph	× 1.60934

Brake Pressure → bar

Unit	Factor
bar	× 1.0
psi	× 0.0689476
kpa	× 0.01

Throttle → 0.0–1.0

• Unit ratio: already 0.0–1.0
• Unit % or values > 1.5: divide by 100
• Unit deg: divide by 100
• Unit rad: divide by 1.745 (100° in radians)

Steering → degrees

• Unit deg: already degrees
• Unit rad: multiply by 180/π

Resampling

Channels have different native frequencies (10 Hz to 200 Hz). Resample to a unified rate (typically 50 Hz) using linear interpolation:

output_count = floor(duration * target_freq) + 1

for i in 0..<output_count:
    t = i / target_freq           // seconds
    src_pos = t * src_freq        // fractional source index
    lo = floor(src_pos)
    hi = min(lo + 1, src_count - 1)
    frac = src_pos - lo
    output[i] = data[lo] + (data[hi] - data[lo]) * frac

Implementation Checklist

1. ☐ Read file, validate magic == 0x40
2. ☐ Parse header strings (date, time, driver, vehicle, venue)
3. ☐ Walk channel linked list from channel_meta_ptr (124-byte blocks)
4. ☐ For each channel: read n_data samples from data_ptr
5. ☐ Float channels (datatype_a == 0x07): read as float32, no conversion
6. ☐ Integer channels: read as int16/int32, apply conversion formula
7. ☐ Parse .ldx companion file for beacon timestamps (microseconds)
8. ☐ Compute laps from consecutive beacon pairs
9. ☐ Map channel names (case-insensitive) to unified fields
10. ☐ Apply unit conversions (speed→km/h, brake→bar, throttle→0-1)
11. ☐ Resample all channels to common frequency
12. ☐ Compute cumulative distance from speed (if no distance channel)

Robustness Notes

• Bounds checking: data_ptr + n_data * datatype may exceed file size — clamp n_data
• Empty channels: n_data == 0 is valid, return empty array
• Missing .ldx: fall back to single-lap mode (entire session = one lap)
• Corrupt linked list: next_addr == 0, next_addr <= current_addr, or next_addr >= file_size all terminate iteration
• Division by zero: scale == 0 → use 1, mul == 0 → use 1
• String encoding: Latin-1 (ISO 8859-1), not UTF-8