Two lessons from chasing one stubborn file. A 60 s stream copy (-ss X -c copy) of an H.264 source
with B-frames lost 230 of its 1500 frames and shifted the content, so every encode of that cut
looked broken (SSIM minimum 0.25) - harnesses must sample with byte copies, never stream copies,
and must prove themselves against a file compared with itself. And when a single file resists
diagnosis, park it and report it instead of stalling a library run on one item.
Two failures from today's library run, both caught, both now handled:
1. The picture gate compared frames by INDEX after an input seek. A seek snaps to a keyframe, and
it snapped to a DIFFERENT keyframe for the source and for the encode - measured: two 1500-frame
decodes whose start times differed by ~10 s, so every frame met the wrong one and a perfectly
good encode scored min SSIM 0.25 (and a file with a hole in its source's timeline scored 0.45).
The window is now cut with the trim filter on absolute PTS (-copyts), so both sides cover
exactly the same interval no matter where the seek lands; a self-comparison then measures
lo=1.0/mean=1.0 (validated), and a frame-count difference >1% is reported as 'gate NOT
APPLICABLE' rather than failing a file whose source is simply missing frames.
2. RaiDrive/Dokan returned from a 403 MB write with NO error while the remote file held 12.5 MB,
and surfaced 'the operation didn't complete within specific time limit' afterwards. The
SHA-256 read-back caught it (nothing was replaced), and it now retries the upload instead of
failing outright. Uploads use 4 MB chunks with a periodic flush; source copies retry 5x with a
longer backoff and smaller chunks.
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.
The previous runner encoded everything at a fixed -cq 27 with -maxrate = 1.5x the FILE bitrate,
which is how a library ended up at 111% of its source size. This replaces the encode step with the
policy the skill documents, and adds the gates that make it a guarantee:
* classify by bpp: <0.025 copy the video (bit-identical), 0.025-0.040 hevc_nvenc, >0.040 libx265
* -maxrate = 1.0x the source's VIDEO bitrate (never the file total) + a post-encode assertion
* SSIM gate: per-frame comparison of a 60 s window against the source, retry once at +2 quality
if it fails, then fail the item (the original is never touched)
* audio: copy when AAC, else AAC at the SOURCE's bitrate (a fixed 256k cancelled the video saving)
* x265 tier pinned to the E-cores; --tier to run tiers separately; --keep-local for a pilot that
touches nothing
* defaults cq31 / crf26 from the measurement below, not cq27
Measured on three real sources (60 s window, video-only): cq27 GROWS two of three files (115%,
119%); cq31 lands at 43-74%; x265 crf26 at 34-67% with min SSIM 0.988-0.993 - and x265 beats NVENC
by 10-22% at matched SSIM. Pinning min SSIM >= 0.996 leaves only cq27, which is bigger than the
source, so ~0.99 is the usable quality frontier and the owner gets to make that call explicitly
(references/hevc-conversion-policy.md section 11, SKILL.md scope section).
Give it a path; it reads the source, picks the recipe, encodes, and verifies the
result before accepting it.
The problem it exists to remove: a file can drop ~23% of its frames in a browser
while r_frame_rate == avg_frame_rate reads EXACTLY equal, so every fps-based check
calls it healthy and it never enters a repair queue. The cause is deterministic and
header-readable -- the MP4 composition-offset table is unusable, either a single
constant ctts entry (PTS == DTS + const) or no ctts box at all (PTS == DTS) -- so the
frame timestamps are in decode order and the decoder's reordered output frames carry
the wrong times.
- three recipes chosen from the source FILE, never the filename: lossless -c copy when
the timeline allows it, AAC-only fix when just the audio is wrong, full HEVC (or
x264 for reach) when the timeline cannot be copied
- quality policy: never upscale; HEVC -cq 27 measured at SSIM 0.9937 ~= source size;
audio copied when already AAC, else AAC 256k
- the two flags that must never be dropped: -fps_mode cfr and -pix_fmt yuv420p
- verified before acceptance: duration, resolution, codec, hvc1 tag, 8-bit, uniform
cadence, no flat composition offsets, full decode pass, and a read-back after the write
- built for cron: lock file (two concurrent NVENC jobs starve one encoder and DROP
FRAMES), idempotent, leaves the input untouched on failure, aborts below 5 GB free
- scripts/selftest.py builds both defect shapes and asserts the detector, including a
Matroska case that must NOT be flagged
Measured on the file that prompted this: 23.0% of frames dropped before, 0.0% after.
hoelee
Hermes Agent