Intra-track segment looping: reuse identical sections

[rancur]

Problem

Currently every phrase in a song generates a unique video segment. A typical 4-minute track has ~15 segments, but many are repeated section types (Drop 1 = Drop 2, Buildup 1 = Buildup 2).

Proposal

Modify _plan_segments() in pipeline.py to detect repeated section types within a single track and reuse the first generated video for subsequent identical sections.

Add a segment_reuse_map keyed by (section_label, energy_bucket, mood_quadrant). When a new segment matches an existing key, copy/symlink the existing video instead of regenerating.

Impact

• Reduces unique segments per track from ~15 to ~6
• Saves ~60% of video generation cost per track
• Zero quality tradeoff for repeated sections

Files to Modify

• src/pipeline.py -- _plan_segments() and generate_for_track()
• src/generator/cache.py -- extend cache key for intra-track reuse

Cost Impact

Before	After	Savings
$23/track	$9.60/track	58%
$115,000 / 5K tracks	$48,000 / 5K tracks	$67,000

Labels: cost-optimization, high-priority