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def calculate_compression_score(
vmaf_score: float,
compression_rate: float,
vmaf_threshold: float,
compression_weight: float = 0.70,
quality_weight: float = 0.30,
soft_threshold_margin: float = 5.0) -> tuple[float, float, float, str]:
"""
Calculate compression score that rewards hitting VMAF threshold with good compression.
Scoring Philosophy:
- Compression is primary goal (70% weight by default)
- VMAF at/above threshold is rewarded with diminishing returns (30% weight)
- 15x compression ratio = 1.0 compression component
- Exceeding VMAF threshold gives modest bonus (not penalty)
Three scoring zones:
1. Below hard cutoff (threshold - 5): Score = 0
2. Soft zone (threshold - 5 to threshold): Gradual recovery
3. Above threshold: Full scoring with quality bonus
Args:
vmaf_score: VMAF quality score (0-100)
compression_rate: Size ratio compressed/original (0-1, lower is better)
vmaf_threshold: Required VMAF threshold (e.g., 85, 90, 95)
compression_weight: Weight for compression component (default: 0.70)
quality_weight: Weight for quality component (default: 0.30)
soft_threshold_margin: Points below threshold before hard cutoff (default: 5.0)
Returns:
Tuple of (final_score, compression_component, quality_component, reason)
where final_score is in range [0.0, 1.0]
"""
# Validate that weights sum to 1.0
if abs(compression_weight + quality_weight - 1.0) > 0.01:
raise ValueError(f"Weights must sum to 1.0, got {compression_weight + quality_weight}")
# Calculate hard cutoff point
hard_cutoff = vmaf_threshold - soft_threshold_margin
# ========================================================================
# CASE 0: No Meaningful Compression - Immediate Failure
# ========================================================================
# If compression_rate >= 0.80 (less than 1.25x compression), this is likely
# the miner returning the same video or minimal compression to exploit high VMAF.
# Zero the entire score to prevent this exploit.
if compression_rate >= 0.80:
compression_ratio = 1 / compression_rate if compression_rate > 0 else 1.0
return 0.0, 0.0, 0.0, f"No meaningful compression (ratio: {compression_ratio:.2f}x, rate: {compression_rate:.2f}). Minimum 1.25x required."
# ========================================================================
# CASE 1: Below Hard Cutoff - Immediate Failure
# ========================================================================
# If VMAF is more than 5 points below threshold, quality is unacceptable
if vmaf_score < hard_cutoff:
return 0.0, 0.0, 0.0, f"VMAF {vmaf_score:.2f} below hard cutoff ({hard_cutoff:.2f})"
# ========================================================================
# CASE 2: Soft Threshold Zone (threshold-5 to threshold)
# ========================================================================
# Gradual recovery zone where both quality and compression matter
if vmaf_score < vmaf_threshold:
# Calculate position in soft zone (0.0 to 1.0)
# Example: VMAF 93 with threshold 95 and margin 5
# soft_zone_position = (93 - 90) / 5 = 0.6
soft_zone_position = (vmaf_score - hard_cutoff) / soft_threshold_margin
"""
Quality factor uses scaled function to reach 0.7 at threshold:
f(x) = 0.7 * x²
- At hard cutoff (x=0): factor = 0.0
- At midpoint (x=0.5): factor = 0.175
- At threshold (x=1): factor = 0.7
This ensures continuity with the above-threshold quality component
which starts at 0.7 when VMAF equals threshold.
"""
quality_factor = 0.7 * (soft_zone_position ** 2)
# Calculate compression component (compression_rate < 0.80 guaranteed by CASE 0)
compression_ratio = 1 / compression_rate
if compression_ratio <= 20:
"""
Compression scoring for 1x to 20x:
f(r) = ((r - 1) / 19) ^ 1.5
Where r is compression ratio (e.g., 5 for 5x compression)
- At 1x: component = 0
- At 2x: component ≈ 0.23
- At 5x: component ≈ 0.65
- At 10x: component ≈ 0.89
- At 15x: component ≈ 0.97
- At 20x: component = 1.0
The exponent 1.5 provides:
- Slow growth initially (encouraging minimum viable compression)
- Steeper growth in practical range (5-15x)
- Reaches 1.0 exactly at 20x
"""
compression_component = ((compression_ratio - 1) / 19) ** 1.5
else:
"""
Bonus for exceptional compression (>20x):
f(r) = 1.0 + 0.3 * ln(r / 20)
Logarithmic bonus rewards exceptional performance:
- At 20x: component = 1.0 (continuous at boundary)
- At 30x: component ≈ 1.12
- At 40x: component ≈ 1.21
- At 60x: component ≈ 1.30 (capped)
Natural log ensures smooth transition from linear region.
"""
compression_component = 1.0 + 0.3 * math.log(compression_ratio / 20)
compression_component = min(1.3, compression_component)
# In soft zone, both compression AND quality factor matter
# If you're below threshold, you need good compression to recover
final_score = compression_component * quality_factor
return min(1.0, final_score), compression_component, quality_factor, f"VMAF {vmaf_score:.2f} in soft zone (quality factor: {quality_factor:.2f})"
# ========================================================================
# CASE 3: Above Threshold - Full Scoring with Quality Bonus
# ========================================================================
else:
# Calculate how much VMAF exceeds threshold
vmaf_excess = vmaf_score - vmaf_threshold
max_vmaf_excess = 100 - vmaf_threshold # Maximum possible excess to VMAF 100
"""
Quality component rewards exceeding threshold with linear interpolation:
f(x) = 0.7 + 0.3 * (x / max_excess)
Where x is VMAF points above threshold:
- At threshold (x=0): component = 0.7
- At threshold + 25% of range: component = 0.775
- At threshold + 50% of range: component = 0.85
- At threshold + 75% of range: component = 0.925
- At VMAF 100: component = 1.0
Example with threshold=85:
- At 85: 0.7 + 0.3 * (0/15) = 0.7
- At 90: 0.7 + 0.3 * (5/15) = 0.8
- At 95: 0.7 + 0.3 * (10/15) = 0.9
- At 100: 0.7 + 0.3 * (15/15) = 1.0
This provides steady linear growth from 0.7 to 1.0 as VMAF approaches perfect quality.
"""
quality_component = 0.7 + 0.3 * min(1.0, vmaf_excess / max_vmaf_excess)
# Calculate compression component (compression_rate < 0.80 guaranteed by CASE 0)
compression_ratio = 1 / compression_rate
if compression_ratio <= 20:
"""
Good compression scoring (1.25x to 20x):
f(r) = ((r - 1.25) / 18.75) ^ 1.2
Starting from 1.25x to give smooth transition from poor zone:
- At 1.25x: component = 0.025
- At 2x: component ≈ 0.24
- At 5x: component ≈ 0.64
- At 10x: component ≈ 0.88
- At 15x: component ≈ 0.96
- At 20x: component = 1.0
The exponent 1.2 provides balanced reward curve.
"""
compression_component = ((compression_ratio - 1.25) / 18.75) ** 1.2 + 0.025
else:
"""
Exceptional compression bonus (>20x):
f(r) = 1.0 + 0.3 * ln(r / 20)
Logarithmic bonus up to 1.3 cap:
- At 20x: component = 1.0 (continuous at boundary)
- At 30x: component ≈ 1.12
- At 40x: component ≈ 1.21
- At 60x: component ≈ 1.30 (capped)
Natural log ensures smooth transition from power region.
"""
compression_component = 1.0 + 0.3 * math.log(compression_ratio / 20)
compression_component = min(1.3, compression_component)
reason_suffix = "" if compression_ratio < 10 else " (excellent compression)"
"""
Final score is weighted combination:
final_score = w_c * compression_component + w_q * quality_component
Default: 70% compression + 30% quality
Capped at 1.0 to maintain normalized scoring
"""
final_score = (compression_weight * compression_component +
quality_weight * quality_component)
final_score = min(1.0, final_score)
return final_score, compression_component, quality_component, f"success{reason_suffix}" |