Add ffprobe checks for grid batch outputs

README.md

@@ -144,6 +144,32 @@ uv run python scripts/zed_batch_svo_grid_to_mp4.py \
 
 The batch grid wrapper mirrors the grid encoder options, skips existing `<segment>/<segment>_grid.mp4` outputs by default, and returns a nonzero exit code if any segment fails.
 
+When you suspect a previous run left behind partial MP4 files, opt into `ffprobe` validation so broken existing outputs are treated as missing instead of skipped:
+
+```bash
+uv run python scripts/zed_batch_svo_grid_to_mp4.py \
+    /workspaces/data/kindergarten \
+    --probe-existing \
+    --jobs 2
+```
+
+Use `--report-existing` to audit existing outputs without launching conversions. The report prints invalid existing files only, while the summary still includes valid and missing counts. This is useful for the partial-write failure mode currently seen as `moov atom not found` in some kindergarten grid MP4s:
+
+```bash
+uv run python scripts/zed_batch_svo_grid_to_mp4.py \
+    /workspaces/data/kindergarten \
+    --report-existing
+```
+
+Use `--dry-run` to preview what the batch wrapper would convert after applying skip logic. Combine it with `--probe-existing` when you want to see which broken existing outputs would be requeued:
+
+```bash
+uv run python scripts/zed_batch_svo_grid_to_mp4.py \
+    /workspaces/data/kindergarten \
+    --probe-existing \
+    --dry-run
+```
+
 #### Expected CSV Input Format
 
 The `--segments-csv` input expects a header row with at least a `segment_dir` column. Extra columns are allowed and ignored by the batch wrapper. `segment_dir` values may be absolute paths or paths relative to the CSV file's parent directory. Use `--csv-root` to override that base directory.