# Motion-subtraction analysis

Dedicated background/motion subtraction pass over the 8 event windows. Methods: MOG2 + KNN background subtractors, temporal frame differencing, court-region mask, connected components, top-motion sheets, heatmaps, overlay/mask videos. Motion evidence is used to support activity and movement timing, not scoring.

## H07 01:12:38–01:12:45 best_highlight_net_action_candidate
- Interpretation: Motion subtraction strengthens H07 as the best action highlight: broad multi-person motion and localized small-motion candidates align with the visually observed late net action / possible defensive scramble.
- Frames analyzed: 210
- Mean motion ratio: 0.0293; max: 0.0539
- Mean player-like components: 3.32; mean small-motion candidates: 9.17
- Overlay clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/overlays/H07_best_highlight_net_action_candidate_motion_overlay.mp4`
- Motion mask clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/masks/H07_best_highlight_net_action_candidate_motion_mask.mp4`
- Heatmap: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/heatmaps/H07_best_highlight_net_action_candidate_motion_heatmap.jpg`
- Top-motion sheet: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/sheets/H07_best_highlight_net_action_candidate_motion_top_sheet.jpg`
- Top motion times: 01:12:40, 01:12:39, 01:12:42, 01:12:41, 01:12:40, 01:12:41

## H03 00:34:31–00:34:43 set_or_controlled_return_candidate
- Interpretation: Motion subtraction supports H03 as an active central exchange; broad player motion aligns with the overhead/set-like interpretation, but ball/contact order remains unresolved.
- Frames analyzed: 360
- Mean motion ratio: 0.0250; max: 0.0634
- Mean player-like components: 2.61; mean small-motion candidates: 6.27
- Overlay clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/overlays/H03_set_or_controlled_return_candidate_motion_overlay.mp4`
- Motion mask clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/masks/H03_set_or_controlled_return_candidate_motion_mask.mp4`
- Heatmap: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/heatmaps/H03_set_or_controlled_return_candidate_motion_heatmap.jpg`
- Top-motion sheet: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/sheets/H03_set_or_controlled_return_candidate_motion_top_sheet.jpg`
- Top motion times: 00:34:39, 00:34:40, 00:34:39, 00:34:40, 00:34:41, 00:34:42

## H04 00:35:35–00:36:10 repeated_exchange_cluster
- Interpretation: Motion subtraction shows sustained motion across the longer H04 cluster, consistent with multiple exchanges/resets rather than one clean rally.
- Frames analyzed: 1050
- Mean motion ratio: 0.0177; max: 0.0852
- Mean player-like components: 2.74; mean small-motion candidates: 6.01
- Overlay clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/overlays/H04_repeated_exchange_cluster_motion_overlay.mp4`
- Motion mask clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/masks/H04_repeated_exchange_cluster_motion_mask.mp4`
- Heatmap: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/heatmaps/H04_repeated_exchange_cluster_motion_heatmap.jpg`
- Top-motion sheet: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/sheets/H04_repeated_exchange_cluster_motion_top_sheet.jpg`
- Top motion times: 00:36:06, 00:36:06, 00:35:40, 00:35:40, 00:35:41, 00:36:05

## H05 00:55:44–00:55:55 multiplayer_exchange_candidate
- Interpretation: Motion subtraction supports a compact multi-player exchange with high action density; some small-object candidates remain ambiguous.
- Frames analyzed: 330
- Mean motion ratio: 0.0734; max: 0.4547
- Mean player-like components: 5.20; mean small-motion candidates: 29.72
- Overlay clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/overlays/H05_multiplayer_exchange_candidate_motion_overlay.mp4`
- Motion mask clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/masks/H05_multiplayer_exchange_candidate_motion_mask.mp4`
- Heatmap: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/heatmaps/H05_multiplayer_exchange_candidate_motion_heatmap.jpg`
- Top-motion sheet: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/sheets/H05_multiplayer_exchange_candidate_motion_top_sheet.jpg`
- Top motion times: 00:55:52, 00:55:49, 00:55:53, 00:55:50, 00:55:50, 00:55:53

## H02 00:13:07–00:13:14 active_exchange_candidate
- Interpretation: Motion subtraction supports an active low/aggressive movement sequence involving ENGLAND #7/white-light but not the outcome.
- Frames analyzed: 210
- Mean motion ratio: 0.0228; max: 0.0503
- Mean player-like components: 2.84; mean small-motion candidates: 5.16
- Overlay clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/overlays/H02_active_exchange_candidate_motion_overlay.mp4`
- Motion mask clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/masks/H02_active_exchange_candidate_motion_mask.mp4`
- Heatmap: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/heatmaps/H02_active_exchange_candidate_motion_heatmap.jpg`
- Top-motion sheet: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/sheets/H02_active_exchange_candidate_motion_top_sheet.jpg`
- Top motion times: 00:13:10, 00:13:11, 00:13:12, 00:13:10, 00:13:12, 00:13:13

## H01 00:12:17–00:12:22 defensive_retrieve_candidate
- Interpretation: Motion subtraction supports a brief low defensive/retrieve candidate but does not prove contact or point outcome.
- Frames analyzed: 150
- Mean motion ratio: 0.0188; max: 0.0367
- Mean player-like components: 2.40; mean small-motion candidates: 5.67
- Overlay clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/overlays/H01_defensive_retrieve_candidate_motion_overlay.mp4`
- Motion mask clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/masks/H01_defensive_retrieve_candidate_motion_mask.mp4`
- Heatmap: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/heatmaps/H01_defensive_retrieve_candidate_motion_heatmap.jpg`
- Top-motion sheet: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/sheets/H01_defensive_retrieve_candidate_motion_top_sheet.jpg`
- Top motion times: 00:12:21, 00:12:21, 00:12:20, 00:12:22, 00:12:19, 00:12:20

## H06 01:06:24–01:06:45 low_defense_candidate
- Interpretation: Motion subtraction captures body movement/low posture but adds little ball evidence; keep as a low-defense candidate, not a confirmed dig.
- Frames analyzed: 630
- Mean motion ratio: 0.0109; max: 0.0486
- Mean player-like components: 1.03; mean small-motion candidates: 9.07
- Overlay clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/overlays/H06_low_defense_candidate_motion_overlay.mp4`
- Motion mask clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/masks/H06_low_defense_candidate_motion_mask.mp4`
- Heatmap: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/heatmaps/H06_low_defense_candidate_motion_heatmap.jpg`
- Top-motion sheet: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/sheets/H06_low_defense_candidate_motion_top_sheet.jpg`
- Top motion times: 01:06:38, 01:06:32, 01:06:38, 01:06:43, 01:06:32, 01:06:43

## H08 01:12:57–01:13:02 short_late_exchange_candidate
- Interpretation: Motion subtraction supports a short late exchange/reset sequence with multiple players involved.
- Frames analyzed: 150
- Mean motion ratio: 0.0224; max: 0.0389
- Mean player-like components: 2.67; mean small-motion candidates: 5.11
- Overlay clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/overlays/H08_short_late_exchange_candidate_motion_overlay.mp4`
- Motion mask clip: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/masks/H08_short_late_exchange_candidate_motion_mask.mp4`
- Heatmap: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/heatmaps/H08_short_late_exchange_candidate_motion_heatmap.jpg`
- Top-motion sheet: `/home/kristjan-variksoo/volleyball-analysis-iS3G8p90TYY/motion_subtraction/sheets/H08_short_late_exchange_candidate_motion_top_sheet.jpg`
- Top motion times: 01:13:00, 01:13:00, 01:12:58, 01:12:59, 01:13:00, 01:13:01

## Limitations

- Background subtraction highlights all motion, including player bodies, camera compression artifacts, tree/background movement, and shadows.
- Small-motion candidates are not reliable volleyball detections by themselves.
- Motion subtraction improves highlight/event timing confidence but still cannot recover score, point winner, or exact contact order without visible scorekeeping or manual 30fps tagging.