MediaPipe Pose Detection

Key Landmarks for Jump Analysis

Lower Body (Primary for Jumps)

Landmark	Left Index	Right Index	Use Case
Hip	23	24	Center of mass, jump height
Knee	25	26	Triple extension, landing
Ankle	27	28	Ground contact detection
Heel	29	30	Takeoff/landing timing
Toe	31	32	Forefoot contact

Upper Body (Secondary)

Landmark	Left Index	Right Index	Use Case
Shoulder	11	12	Arm swing tracking
Elbow	13	14	Arm action
Wrist	15	16	Arm swing timing

Reference Points

Landmark	Index	Use Case
Nose	0	Head position
Left Eye	2	Face orientation
Right Eye	5	Face orientation

Confidence Thresholds

Default Settings

min_detection_confidence = 0.5  # Initial pose detection
min_tracking_confidence = 0.5   # Frame-to-frame tracking

Quality Presets (auto_tuning.py)

Preset	Detection	Tracking	Use Case
fast	0.3	0.3	Quick processing, tolerates errors
balanced	0.5	0.5	Default, good accuracy
accurate	0.7	0.7	Best accuracy, slower

Tuning Guidelines

• Increase thresholds when: Jittery landmarks, false detections
• Decrease thresholds when: Missing landmarks, tracking loss
• Typical adjustment: ±0.1 increments

Common Issues and Solutions

Landmark Jitter

Symptoms: Landmarks jump erratically between frames

Solutions:

1. Apply Butterworth low-pass filter (cutoff 6-10 Hz)
2. Increase tracking confidence
3. Use One-Euro filter for real-time applications

# Butterworth filter (filtering.py)
from kinemotion.core.filtering import butterworth_filter
smoothed = butterworth_filter(landmarks, cutoff=8.0, fps=30)

# One-Euro filter (smoothing.py)
from kinemotion.core.smoothing import one_euro_filter
smoothed = one_euro_filter(landmarks, min_cutoff=1.0, beta=0.007)

Left/Right Confusion

Symptoms: MediaPipe swaps left and right landmarks mid-video

Cause: Occlusion at 90° lateral camera angle

Solutions:

1. Use 45° oblique camera angle (recommended)
2. Post-process to detect and correct swaps
3. Use single-leg tracking when possible

Tracking Loss

Symptoms: Landmarks disappear for several frames

Causes:

• Athlete moves out of frame
• Fast motion blur
• Occlusion by equipment/clothing

Solutions:

1. Ensure full athlete visibility throughout video
2. Use higher frame rate (60+ fps)
3. Interpolate missing frames (up to 3-5 frames)

# Simple linear interpolation for gaps
import numpy as np
def interpolate_gaps(landmarks, max_gap=5):
    # Fill NaN gaps with linear interpolation
    for i in range(landmarks.shape[1]):
        mask = np.isnan(landmarks[:, i])
        if mask.sum() > 0 and mask.sum() <= max_gap:
            landmarks[:, i] = np.interp(
                np.arange(len(landmarks)),
                np.where(~mask)[0],
                landmarks[~mask, i]
            )
    return landmarks

Low Confidence Scores

Symptoms: Visibility scores consistently below threshold

Causes:

• Poor lighting (backlighting, shadows)
• Low contrast clothing vs background
• Partial occlusion

Solutions:

1. Improve lighting (front-lit, even)
2. Ensure clothing contrasts with background
3. Remove obstructions from camera view

Video Processing (video_io.py)

Rotation Handling

Mobile videos often have rotation metadata that must be handled:

# video_io.py handles this automatically
# Reads EXIF rotation and applies correction
from kinemotion.core.video_io import read_video_frames

frames, fps, dimensions = read_video_frames("mobile_video.mp4")
# Frames are correctly oriented regardless of source

Manual Rotation (if needed)

# FFmpeg rotation options
ffmpeg -i input.mp4 -vf "transpose=1" output.mp4  # 90° clockwise
ffmpeg -i input.mp4 -vf "transpose=2" output.mp4  # 90° counter-clockwise
ffmpeg -i input.mp4 -vf "hflip" output.mp4        # Horizontal flip

Frame Dimensions

Always read actual frame dimensions from first frame, not metadata:

# Correct approach
cap = cv2.VideoCapture(video_path)
ret, frame = cap.read()
height, width = frame.shape[:2]

# Incorrect (may be wrong for rotated videos)
width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))

Coordinate Systems

MediaPipe Output

• Normalized coordinates: (0.0, 0.0) to (1.0, 1.0)
• Origin: Top-left corner
• X: Left to right
• Y: Top to bottom
• Z: Depth (relative, camera-facing is negative)

Conversion to Pixels

def normalized_to_pixel(landmark, width, height):
    x = int(landmark.x * width)
    y = int(landmark.y * height)
    return x, y

Visibility Score

Each landmark has a visibility score (0.0-1.0):

• 0.5: Likely visible and accurate

• < 0.5: May be occluded or estimated
• = 0.0: Not detected

Debug Overlay (debug_overlay.py)

Skeleton Drawing

# Key connections for jump visualization
POSE_CONNECTIONS = [
    (23, 25), (25, 27), (27, 29), (27, 31),  # Left leg
    (24, 26), (26, 28), (28, 30), (28, 32),  # Right leg
    (23, 24),                                  # Hips
    (11, 23), (12, 24),                       # Torso
]

Color Coding

Element	Color (BGR)	Meaning
Skeleton	(0, 255, 0)	Green - normal tracking
Low confidence	(0, 165, 255)	Orange - visibility < 0.5
Key angles	(255, 0, 0)	Blue - measured angles
Phase markers	(0, 0, 255)	Red - takeoff/landing

Performance Optimization

Reducing Latency

1. Use model_complexity=0 for fastest inference
2. Process every Nth frame for batch analysis
3. Use GPU acceleration if available

import mediapipe as mp

pose = mp.solutions.pose.Pose(
    model_complexity=0,      # 0=Lite, 1=Full, 2=Heavy
    min_detection_confidence=0.5,
    min_tracking_confidence=0.5,
    static_image_mode=False  # False for video (uses tracking)
)

Memory Management

• Release pose estimator after processing: pose.close()
• Process videos in chunks for large files
• Use generators for frame iteration

Integration with kinemotion

File Locations

• Pose estimation: src/kinemotion/core/pose.py
• Video I/O: src/kinemotion/core/video_io.py
• Filtering: src/kinemotion/core/filtering.py
• Smoothing: src/kinemotion/core/smoothing.py
• Auto-tuning: src/kinemotion/core/auto_tuning.py

Typical Pipeline

Video → read_video_frames() → pose.process() → filter/smooth → analyze

Manual Observation for Validation

During development, use manual frame-by-frame observation to establish ground truth and validate pose detection accuracy.

When to Use Manual Observation

1. Algorithm development: Validating new phase detection methods
2. Parameter tuning: Comparing detected vs actual frames
3. Debugging: Investigating pose detection failures
4. Ground truth collection: Building validation datasets

Ground Truth Data Collection Protocol

Step 1: Generate Debug Video

uv run kinemotion cmj-analyze video.mp4 --output debug.mp4

Step 2: Manual Frame-by-Frame Analysis

Open debug video in a frame-stepping tool (QuickTime, VLC with frame advance, or video editor).

Step 3: Record Observations

For each key phase, record the frame number where the event occurs:

=== MANUAL OBSERVATION: PHASE DETECTION ===

Video: ________________________
FPS: _____ Total Frames: _____

PHASE DETECTION (frame numbers)
| Phase | Detected | Manual | Error | Notes |
|-------|----------|--------|-------|-------|
| Standing End | ___ | ___ | ___ | |
| Lowest Point | ___ | ___ | ___ | |
| Takeoff | ___ | ___ | ___ | |
| Peak Height | ___ | ___ | ___ | |
| Landing | ___ | ___ | ___ | |

LANDMARK QUALITY (per phase)
| Phase | Hip Visible | Knee Visible | Ankle Visible | Notes |
|-------|-------------|--------------|---------------|-------|
| Standing | Y/N | Y/N | Y/N | |
| Countermovement | Y/N | Y/N | Y/N | |
| Flight | Y/N | Y/N | Y/N | |
| Landing | Y/N | Y/N | Y/N | |

Phase Detection Criteria

Standing End: Last frame before downward hip movement begins

• Look for: Hip starts descending, knees begin flexing

Lowest Point: Frame where hip reaches minimum height

• Look for: Deepest squat position, hip at lowest Y coordinate

Takeoff: First frame where both feet leave ground

• Look for: Toe/heel landmarks separate from ground plane
• Note: May be 1-2 frames after visible liftoff due to detection lag

Peak Height: Frame where hip reaches maximum height

• Look for: Hip at highest Y coordinate during flight

Landing: First frame where foot contacts ground

• Look for: Heel or toe landmark touches ground plane
• Note: Algorithm may detect 1-2 frames late (velocity-based)

Landmark Quality Assessment

For each landmark, observe:

Quality	Criteria
Good	Landmark stable, positioned correctly on body part
Jittery	Landmark oscillates ±5-10 pixels between frames
Offset	Landmark consistently displaced from actual position
Lost	Landmark missing or wildly incorrect
Swapped	Left/right landmarks switched

Recording Observations Format

When validating, provide structured data:

## Ground Truth: [video_name]

**Video Info:**
- Frames: 215
- FPS: 60
- Duration: 3.58s
- Camera: 45° oblique

**Phase Detection Comparison:**

| Phase | Detected | Manual | Error (frames) | Error (ms) |
|-------|----------|--------|----------------|------------|
| Standing End | 64 | 64 | 0 | 0 |
| Lowest Point | 91 | 88 | +3 (late) | +50 |
| Takeoff | 104 | 104 | 0 | 0 |
| Landing | 144 | 142 | +2 (late) | +33 |

**Error Analysis:**
- Mean absolute error: 1.25 frames (21ms)
- Bias detected: Landing consistently late
- Accuracy: 2/4 perfect, 4/4 within ±3 frames

**Landmark Issues Observed:**
- Frame 87-92: Hip jitter during lowest point
- Frame 140-145: Ankle tracking unstable at landing

Acceptable Error Thresholds

At 60fps (16.67ms per frame):

Error Level	Frames	Time	Interpretation
Perfect	0	0ms	Exact match
Excellent	±1	±17ms	Within human observation variance
Good	±2	±33ms	Acceptable for most metrics
Acceptable	±3	±50ms	May affect precise timing metrics
Investigate	>3	>50ms	Algorithm may need adjustment

Bias Detection

Look for systematic patterns across multiple videos:

Pattern	Meaning	Action
Consistent +N frames	Algorithm detects late	Adjust threshold earlier
Consistent -N frames	Algorithm detects early	Adjust threshold later
Variable ±N frames	Normal variance	No action needed
Increasing error	Tracking degrades	Check landmark quality

Integration with basic-memory

Store ground truth observations:

# Save validation results
write_note(
    title="CMJ Phase Detection Validation - [video_name]",
    content="[structured observation data]",
    folder="biomechanics"
)

# Search previous validations
search_notes("phase detection ground truth")

# Build context for analysis
build_context("memory://biomechanics/*")

Example: CMJ Validation Study Reference

See basic-memory for complete validation study:

• biomechanics/cmj-phase-detection-validation-45deg-oblique-view-ground-truth
• biomechanics/cmj-landing-detection-bias-root-cause-analysis
• biomechanics/cmj-landing-detection-impact-vs-contact-method-comparison

Key findings from validation:

• Standing End: 100% accuracy (0 frame error)
• Takeoff: ~0.7 frame mean error (excellent)
• Lowest Point: ~2.3 frame mean error (variable)
• Landing: +1-2 frame consistent bias (investigate)