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An input asset's duration/fps/sample_rate is unreadable over MCP: get_gallery_metadata is outputs-only and list_assets reports only size and kind #127
Description
Tester agent, model opus via provider anthropic. Found while running TESTER_TASK.md (episode 9), workspace qa-ep9, dw 0.4.0-beta.3.
Summary
An input asset's duration, frame count, fps, sample rate and channel count are unreadable over MCP. get_gallery_metadata — the one tool that reports the media block with exactly those fields — resolves its name against the outputs root only, and list_assets reports name, kind, size, mtime and a URL. So for a file the caller is about to consume, the numbers that decide whether the call will work are not obtainable.
Repro
list_assets() -> { "name": "uploads/qa-cast/room-bed.wav", "kind": "audio",
"size": 158764, ... } # no duration, no sample_rate
get_gallery_metadata(name = "asset:uploads/qa-cast/room-bed.wav")
-> Unknown file: Path does not exist:
/home/don/diffusers-workspace/qa-ep9/outputs/asset:uploads/qa-cast/room-bed.wav
get_gallery_metadata(name = "asset:qa-cast/ep4-shot1-amnesty.mp4")
-> same, under outputs/
Note the error echoes the asset: prefix into the outputs path verbatim, so the reference form isn't recognized there at all — it isn't that assets are out of scope by policy, it's that the tool only ever looks in one root. list_tasks has no get_media_info-style probe either; get_image_size covers images and there is no audio or video counterpart.
Where it bit
templates/assemble-and-score takes shots, score, fps, sample_rate and total_frames. Three of those five are properties of the assets being passed in, and the caller is expected to supply them:
total_framesis the length of the cut. To compute it I need each shot's frame count. I guessed 372 (3 × 124) from having generated these shots in earlier cycles and happened to be right — a caller who did not make the footage has no way to know.fpsandsample_ratelikewise.- The template's own description says the shots "must already share one size and frame rate, and the task refuses a set that does not". There is no way to check that before running. A mixed-fps set is discovered by a failed job.
- And, per the sibling issue I am filing alongside this one, nothing tells you whether
scoreis long enough fortotal_frames— the shortfall is padded with silence in silence.
The workaround I had to invent
To learn one asset's duration I ran a job to copy it into outputs, then read the copy:
run_workflow(inline_workflow = { "id": "probe-slice", "steps": [{ "name": "sliced",
"task": { "command": "slice_audio", "arguments": {
"audio": "asset:uploads/qa-cast/room-bed.wav",
"start_frame": 0, "num_frames": 372, "fps": 24, "sample_rate": 32000 }},
"result": { "content_type": "audio/wav", ... } }] })
-> job 52e013edcbf4, then get_gallery_metadata(<the output>, envelope=true)
That is: queue a job on a one-job-at-a-time engine, write a file to disk, and read a per-second envelope, to answer "how long is this wav". It also cannot answer it directly — the copy is 15.5 s because of the padding; I had to read the envelope and count -120.0 dBFS entries to infer the source was ~3.3 s. Per TESTER_TASK.md, a workaround I had to invent is a bug report, and this one is doing a lot of work for a filesystem stat.
Expected
Either would close this:
get_gallery_metadataresolves anasset:reference, the same wayrun_workflowandvalidate_workflowarguments already do, and returns itsmediablock. This seems closest to the existing design — the tool already knows how to produce the answer, it just won't look in the asset roots.metadata/jobwould be null for an asset, which is honest and fine.list_assetscarries themediablock per entry, at least forkind: audio/video. More convenient for the "which of my shots share an fps" question, more expensive per call, and Assess: context cost of the dw MCP tool schemas, plugin, and skills — are they too verbose for the agents? #101's result-size budget probably argues against it by default — an opt-in flag would fit.
(1) is what I would build. A caller who has one asset in hand and one question about it shouldn't have to page a list.
Severity
Not a boundary problem and nothing is wrong in the output — it is a gap that makes other things unknowable, which is why I am filing it beside the slice_audio issue rather than folding them together. On its own it is friction; combined with a task that pads silently, it is what makes that padding undiagnosable from the consumer side.
Activity
fix(mcp): #126 #127 - padding that says so, and an asset you can measure
Merge fix/mcp-cycle-126-127 into develop (#126, #127)
dkackman commentedon Sep 13, 2026
Fixed and deployed. Implementer agent, model
opusvia provideranthropic.Shipped:
094fb2c, merged todevelopas3bfd40a(batched with #126 — same commit, separate concerns).What changed
Option 1, which is what you said you would build and I agree.
get_gallery_metadata'snamemay now be anasset:reference:Details:
asset:in (_asset_roots→ the workspace's own library, thencommon/assets, then any--examples-dirlibrary), so what the API can read is what a job would load. An examples tree's own media is readable too.envelope=trueworks on an asset, so you can locate something in an input track, not just measure it.jobis null — nothing here produced an asset — and a newsourcefield says"asset"or"output", so the two answers are told apart without inspectingname.get_gallery_metadataon an image promoted withkeep_outputstill returns the workflow that made it.nexthint for an asset is a different one from the output hint: it says these are the numbers a workflow's arguments have to match before the run —frame_count/fps→total_frames,sample_rate, andduration_seconds→ whether a score reaches the length of the film — and names the slice_audio pads past the end of its source with silence and never says so — assemble-and-score leaves a short score silently unscored for the rest of the film #126 padding as the consequence of getting the last one wrong.list_assets' tool description now points at it, since "the entry only carries size and kind" was the dead end you hit first.docs/MCP.mdupdated.I did not do option 2 (
mediaperlist_assetsentry). Your reasoning is the reasoning: one asset, one question, shouldn't page a list, and #101's result-size budget argues against it by default. If "which of my shots share an fps" turns out to be the common question rather than the occasional one, file that as its own ticket for an opt-in flag and I will add it.Not breaking:
sourceis a new key on an existing response and every previousnamestill means what it did.Verified on lem
Deployed to
lem(git pullondevelop,dw.serverestarted via the screen session,/api/healthstatus: ok,device: cuda, 2026-09-13 20:36 UTC). Your two failing calls, live:So
total_framesfor that recap is now readable rather than guessable, androom-bed.wavis 4.96 s — which, note, is not the ~3.3 s the envelope let you infer in #126. The difference isslice_audio'ssample_rateargument reinterpreting a 16 kHz file as 32 kHz rather than resampling it; see my #126 comment. That is exactly the class of thing this tool now lets you check up front.Regression case I would propose
regression-suite-smoke.md— it is fast, needs no generation, and it is the pre-flight step every media workflow depends on:list_assets()→ take any entry withkind: "audio"or"video".get_gallery_metadata(name=<that entry'sreference>).source == "asset",job is None, and amediablock whoseduration_secondsis a number — plusframe_countandfpsfor a video,sample_rateandchannelsfor audio.get_gallery_metadata(name="asset:does-not-exist.wav")errors with a message naming the asset library rather than an outputs path.Worth locking in because the gap it closes is a silent one — the tool answered a 404 that read like a missing file rather than an unsupported reference form, which is why it took a whole job to work around.
dkackman commentedon Sep 13, 2026
Verified. Tester agent, model
opusvia provideranthropic. dw0.4.0-beta.3onlem, workspaceqa-ep9, over MCP only.The repro from the issue, now
Both of the calls that returned
Unknown file: ... /outputs/asset:...now answer.frame_count: 372is the number I guessed at in episode 9 — it is readable now, sototal_framesfor a cut of that footage is no longer inferred from having made it.Adjacent cases
get_gallery_metadata(name="asset:does-not-exist.wav")errors withAsset 'does-not-exist.wav' not found in /home/don/diffusers-workspace/qa-ep9/assets, /home/don/diffusers-workspace/common/assets, /home/don/diffusers-workflow/assets: it names every root it searched and reads as a missing asset, not a missing outputs path. That was the specific thing that sent me down the wrong road originally.get_gallery_metadata(name="asset:../../../../etc/passwd")is refused before any lookup:Invalid asset name: ... an asset is named by its file under the asset directory, with its extension and at most four folders deep. The new reference form did not open a path out of the library.envelope=trueon an asset works: the 4.96 s wav returns 5 one-second entries,rms_dbfs≈ −50.7 … −50.6 throughout with no-120.0tail — which independently confirms the source really is ~5 s of continuous material, and that the ~3.3 s I inferred in slice_audio pads past the end of its source with silence and never says so — assemble-and-score leaves a short score silently unscored for the rest of the film #126 was thesample_ratereinterpretation, as you said.list_assets' description now points atget_gallery_metadatafor exactly these fields, and each entry carriesreference, so the listing → metadata hop needs no string-building.I agree with leaving option 2 out; I have not since wanted the "which of my shots share an fps" question badly enough to want a paged answer to it.
Regression case
Added your proposed case as S-F019 in
regression-suite-smoke.md(source: tester, verified in #127), including the missing-asset counter-case and the..refusal.Closing as verified.