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library_run: --origin-root to redo files the old settings bloated, sourced from the snapshot

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The old runner (fixed -cq 27 + fixed 256k audio + maxrate at 1.5x the FILE bitrate) left 54 files
BIGGER than their originals - the worst at 124.8%. Re-encoding those from their current HEVC would
be second-generation loss, so the source must be the pre-conversion original; a dated snapshot of
the library holds it (582 files / 324 GiB measured).

A file already HEVC is now re-done only when it is bigger than its original (>1.01x), which makes
the run idempotent with no extra state. The tier and every gate use the ORIGINAL, dst stays the
live path, and os.remove(src) is suppressed whenever the source came from the origin tree so the
archive of originals can never be deleted by a replace.
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hoelee
2026-10-07 06:11:26 +08:00
parent 97f34b90e7
commit 6a60bb92c4
3 changed files with 69 additions and 10 deletions
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references/hevc-conversion-policy.md
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@@ -256,6 +256,31 @@ Defaults that follow from this, and the gates that enforce them, are in `scripts
video bitrate may not exceed the source's), a one-step quality retry when the SSIM gate fails, and
`-maxrate` = 1.0x the source's **video** bitrate.
## 12. Re-doing files the old settings bloated (use the ORIGINAL, not the converted file)
When a library was already converted with the wrong settings, the output is **bigger than the
original** and re-encoding it again would be a second-generation loss. The fix is to redo it from
the **pre-conversion original**, which usually still exists in a dated snapshot of the library
(measured: a 2026-09-25 snapshot held all 582 files / 324 GiB of the course library).
Measured audit of such a set (54 files converted at `-cq 27` + a fixed 256k audio):
| by the ORIGINAL's bpp | files | live/original | what they needed |
|---|---|---|---|
| copy (<0.025) | **25** | up to **124.8%** | no video re-encode at all - the video should have been copied |
| nvenc (0.025-0.040) | 26 | 106-122% | cq 31 instead of 27 |
| x265 (>0.040) | 3 | - | crf 26 |
`scripts/library_run.py --origin-root <snapshot-tree>` implements this safely:
* a file whose live copy is already HEVC is re-done **only if it is bigger than its original**
(`> 1.01x`); otherwise it is skipped - so the run is idempotent without any extra bookkeeping;
* the encode reads the **original**, the tier is classified from the **original's** bpp, and the
gates compare against the **original** - the converted file is never used as a reference;
* `dst` stays the live path, so the output replaces the (bloated) converted file;
* **the original is never modified or deleted** - `os.remove(src)` is suppressed whenever the
source came from the origin tree. Getting this backwards would destroy the only clean copy.
## 9. CPU and GPU tiers in parallel
Different tiers can encode **at the same time** — NVENC is a fixed-function ASIC, x265 is CPU.