ffrwd/describe

Three video describers and one embedder over a file, hosted in wasm: clips and sounds read the picture and the sound into rows and vectors, embed/embed_text put the same 384-d space under a row or a search prompt, embed_clip/embed_clip_text do the same in X-CLIP's 512-d space, and find.sql ranks one against the other with cos_similarity. Speech is not this package's job - it composes ffrwd/whisper and ffrwd/vad instead of shipping a third model for it.

Requires ffrwd 0.30, whose ffrwd/wasm is 0.19.1.

The four modules are built and run: target/wasm32-wasip2/release/{clips,sounds,embed,embed_clip}.wasm, all nodes of the ffrwd:av@0.19.1 world, and clips_gpu.wasm, clips' source built beside ffrwd:gpu. ffrwd install is the whole of the setup.

The functions

• clips(v, cuts => <rows>) returns STRUCT(start_t number, end_t number, vector vector)[]: a row a shot, or a row every ten seconds of a longer one, each leaving when its stretch ends. cuts is a {shot} row a frame from a detector over the same picture, ffrwd.shots.simple_detector(v); left out, the whole input is one shot. No picture leaves.
• clips_gpu(v, cuts => <rows>, memory DEFAULT 'gpu') returns clips' rows, the host making each frame the module keeps into the tower's input and joining the eight, so the module never reads the picture. With memory => 'gpu' the picture stays on the GPU; each kept frame's centre square is resized and normalised there, and where the tower's session reads the device's memory the eight are joined on the device and bound to it in place. The frame's centre square is resized in one pass where clips resizes and then crops, and nothing is rounded to 8 bits, so a vector agrees with clips' to a cosine of 0.994 to 0.9999 on a five-shot test clip at 1080p and 4K, and ranks shots the same way. cuts comes from ffrwd.shots.simple_detector_gpu(v) over the same picture. It imports ffrwd:gpu, so it runs where the sidecar has GPU support, and needs ffrwd 0.30.
• sounds(a, threshold DEFAULT 0.3, top DEFAULT 3) returns cue[]: up to top AudioSet labels a ten-second window, windows half a window apart, each leaving with its window. No sound leaves.
• embed(rows) and embed_clip(rows) read cues and write STRUCT(start_t number, end_t number, vector vector)[], a vector a cue at the cue's own time. embed_text(prompt) and embed_clip_text(prompt) are the same models over one prompt, at compile time, from the same module files.

A reader takes the picture and the sound from the source, and the rows from the call: ffrwd.describe.clips(f.video[1], ffrwd.shots.simple_detector(f.video[1])).

Where the vectors go

A described file carries its vectors in its own encoded video packets, as SEI messages in H.264 and HEVC and a metadata OBU in AV1, written by ffrwd/index's weave. The Matroska vector track this package used to write is gone. What that changes for a caller:

• The destination is any container, not an .mkv. MP4 takes the same query.
• A described file survives -c copy, a -ss cut and a UNION ALL, which the track never did.
• find.sql reads the vectors back with ffrwd.index.records, a sink the compiler runs while the query compiles. It copies the keyframes alone: on the file below, 0.19% of the bytes.
• Nothing about the file is ffrwd's. The format is SPEC.md, and ffrwd-index read --mp4 film.described.mp4 prints every record and every space declaration without ffrwd involved.

A space declaration says which model made the vectors and which model turns a search into the same space. Those are two different networks for the clip space - X-CLIP's video tower wrote the vectors, its text tower embeds the prompt - and one network reached twice for the text spaces. The URIs and the digests are this package's own models table, written into the recipe as the spaces literal weave reads.

Models

X-CLIP

Function: ffrwd.describe.clips(), ffrwd.describe.embed_clip(), ffrwd.describe.embed_clip_text()

Model: microsoft/xclip-base-patch16-kinetics-600, exported by us to imbcmdth/xclip-onnx.

License: MIT

all-MiniLM-L6-v2

Function: ffrwd.describe.embed(), ffrwd.describe.embed_text()

Model: Xenova/all-MiniLM-L6-v2

License: Apache-2.0

AST

Function: ffrwd.describe.sounds()

Model: onnx-community/ast-finetuned-audioset-10-10-0.4593-ONNX

License: BSD-3-Clause

---

Recipes

Four, in two pairs. One pair reads a file that has sound, the other a file that does not, because the dialect has no way to make a stream optional inside one query: f.audio[1] on a silent source is STREAM_NOT_FOUND: 'f.audio[1]' does not exist, at compile time, before anything runs. Splitting the recipe is the whole fix. describe-video-gpu is describe-video with simple_detector_gpu and clips_gpu.

recipe	source	writes
describe	has audio	video with vectors woven in, the audio, and two caption tracks
describe-video	any	video with vectors woven in
describe-video-gpu	any	describe-video's file, the shots and vectors made on the GPU
find	described, has audio	the matching spans, video and audio
find-video	described	the matching spans, video alone

ffrwd run ffrwd/describe:describe-video -v src=film.mp4 -v dest=film.described.mp4
ffrwd run ffrwd/describe:find-video -v src=film.described.mp4 -v prompt='a car driving at night' -v threshold=0.24 -v dest=clips.mp4

What each container gets

describe writes the AudioSet labels and the transcript as caption tracks beside the video and the audio. They are text, not vectors: find never reads them, and they are there to be read by a person or by unnest(f.cues).

Both columns are written without an alias. An alias on a cue column is the track's TITLE, and a title is Matroska's: every other container rewrites or drops it, so ffrwd refuses a titled track anywhere but an .mkv. Untitled, the same column writes wherever captions do. So:

• .mkv: the video, the audio, and two WebVTT subtitle tracks, in SELECT order - the sound labels first, the transcript second, neither carrying a name.
• .mp4: the same four streams, the captions as mov_text, in the same order.

Naming them again would cost MP4, which is the container this rewrite was for.

The three spaces

describe declares and weaves three. weave has an input per declared space, named for it, and the call binds each producer to its space by name: clip => ..., sound => ..., speech => ....

space	modality	dims	model	query
clip	picture	512	X-CLIP video tower	X-CLIP text tower
sound	sound-text	384	all-MiniLM-L6-v2	the same
speech	speech	384	all-MiniLM-L6-v2	the same

clip is the one whose two models differ: the video tower wrote the vectors and the text tower is what a search goes through. sound and speech are the same embedder over two kinds of text, and they are two spaces rather than one because a declaration carries one modality, and a reader that wanted only what was said could not tell them apart under one id.

describe-video declares one. A space declared to weave rides every keyframe whether a record uses it or not, so a picture-only file described by the three-space recipe would tell every later reader it carries vectors it does not have.

The audio is copied

describe stream-copies the audio. The packets in the output are the source's own bytes, the codec is the source's codec, and the file is the source's size plus what the records cost. That holds even though sounds and vad read the same audio on the way past: ffrwd opens the source again for the stream it is copying rather than taking it off the pipe those two modules read.

Each model runs once

The labels and the transcript are read twice, as caption tracks and under embed, and each is one node: a call written twice in one query is one call, and its rows go to both readers.

Which space is which

A record carries a numeric space id, and weave hands ids out in the order its space table declares them, from zero. find does not rely on that. It joins ffrwd.index.spaces, which reads the declarations out of the file's first packet, and selects on modality. An id is a position in one producer's table; a described file outlives the recipe that wrote it, and may be remuxed, cut, joined to another file, or written by something that is not this package. modality is a field of the format and means the same thing in every file. The extra read is one packet.

A run

Sixty seconds of H.264 at 23.976 fps with a pink-noise AAC track, 45266864 bytes. Trimmed output of the real commands, on 2026-09-20, against ffrwd 0.18.0 and every package resolved from the registry.

$ ffrwd run ffrwd/describe:describe -v src=toned.mp4 -v dest=described.mp4

Fifteen records in three spaces: thirteen shots, one sound label, one transcript cue. 34 seconds to MP4, 29 to Matroska, with the models already in the cache. The described MP4 is 45297349 bytes, so the records cost the video stream 29341 bytes, 0.066% of it, and the same in both containers. Every picture is the source's own: framemd5 over the decoded video agrees across the source, the described MP4, the described Matroska and the same query with the weave call taken out, all 1438 frames of it, and every video packet's presentation time, decode time and duration is the unwoven query's. The audio is the source's own packets, byte for byte, in the source's own codec.

$ ffrwd-index read --mp4 described.mp4
{"space":{"id":0,"dims":512,"encoding":"i8","unit_length":false,"modality":"picture","source":0,
  "model":"hf:imbcmdth/xclip-onnx@649f3c91b59cd24be316dc505e26eacf5cd00801/video_tower.onnx",
  "model_hash":"87a87b51ae52efa549e6e48f3a3b41f4",
  "query":"hf:imbcmdth/xclip-onnx@649f3c91b59cd24be316dc505e26eacf5cd00801/text_tower.onnx",
  "query_hash":"c14df0fdda1ba530330e278b8fabeb0b","producer":"ffrwd/describe 0.2.0"}}
{"space":{"id":1,"dims":384,"encoding":"i8","unit_length":false,"modality":"sound-text","source":0,
  "model":"hf:Xenova/all-MiniLM-L6-v2@751bff37182d3f1213fa05d7196b954e230abad9/onnx/model.onnx",
  "model_hash":"759c3cd2b7fe7e93933ad23c4c9181b7",
  "query":"hf:Xenova/all-MiniLM-L6-v2@751bff37182d3f1213fa05d7196b954e230abad9/onnx/model.onnx",
  "query_hash":"759c3cd2b7fe7e93933ad23c4c9181b7","producer":"ffrwd/describe 0.2.0"}}
{"space":{"id":2,"dims":384,"encoding":"i8","unit_length":false,"modality":"speech","source":0,
  "model":"hf:Xenova/all-MiniLM-L6-v2@751bff37182d3f1213fa05d7196b954e230abad9/onnx/model.onnx",
  "model_hash":"759c3cd2b7fe7e93933ad23c4c9181b7",
  "query":"hf:Xenova/all-MiniLM-L6-v2@751bff37182d3f1213fa05d7196b954e230abad9/onnx/model.onnx",
  "query_hash":"759c3cd2b7fe7e93933ad23c4c9181b7","producer":"ffrwd/describe 0.2.0"}}
described.mp4: scan keyframes: 30 of 1438 samples, 84488 of 45297349 bytes read (0.19% of the file), 36 seeks

(each space is one line in the file; wrapped here.)

Then two searches, one aimed at the picture and one at the sound. The same recipe serves both: the branches are told apart by modality, and the ones a prompt does not clear drop out.

$ ffrwd compile -f recipes/find.sql -v src=described.mp4 \
    -v prompt='a car driving at night' -v threshold=0.23 -v dest=found.mp4
... trim=start=-0.083:end=3.838 ... trim=start=23.315:end=25.276
... trim=start=31.449:end=38.122 ... trim=start=41.167:end=43.419
... trim=start=46.338:end=53.596 ...

$ ffrwd compile -f recipes/find.sql -v src=described.mkv \
    -v prompt='a hiss of static noise' -v threshold=0.30 -v dest=found.mkv
... trim=start=-0.083:end=9.917 ... atrim=start=-0.083:end=9.917 ...

Five spans from the picture prompt, 22.065 seconds cut out of sixty, and the same five off the .mkv. One span from the sound prompt, 10 seconds, and it is the sound record: that prompt scores 0.496 against the sound space and 0.014 against the speech space, so only one branch survives the threshold.

The compile of find is 5 seconds on the machine this ran on, most of it the two text towers loading; find-video, which the picture prompt alone needs, compiled a described file in 2.8 seconds with one tower. The read of the file's own records is the keyframe scan above and is not where the time goes.

The silent pair over the same picture without its audio track: 9 seconds to describe, thirteen records in the one picture space, and find-video over the result cuts the same five spans the three-space file gave.

The same three rankings over the binary32 the models produced, before the 8-bit encoding and before the file:

$ ffrwd-index search --rows rows.ndjson --space 1 --query query_clip.json --top 5
{"rank":1,"score":0.247439,"start_t":41.250,"end_t":43.502,"space":1,"record_id":8}
{"rank":2,"score":0.243536,"start_t":31.532,"end_t":38.205,"space":1,"record_id":6}
{"rank":3,"score":0.240230,"start_t":46.421,"end_t":53.679,"space":1,"record_id":10}
{"rank":4,"score":0.238564,"start_t":23.398,"end_t":25.359,"space":1,"record_id":4}
{"rank":5,"score":0.236714,"start_t":0.000,"end_t":3.921,"space":1,"record_id":0}

$ ffrwd-index search --rows rows.ndjson --space 3 --query query_noise.json --top 3
{"rank":1,"score":0.496058,"start_t":0.000,"end_t":10.000,"space":3,"record_id":0}

$ ffrwd-index search --rows rows.ndjson --space 2 --query query_noise.json --top 3
{"rank":1,"score":0.013573,"start_t":30.000,"end_t":36.000,"space":2,"record_id":0}

Out of the file the same three read 0.247323, 0.496017 and 0.014074, in the same order, with the clip space's five records ranked the same way. The scores differ in the third or fourth decimal, which is the 8-bit encoding, and the spans by 83 milliseconds, which is two frames at 23.976 fps: the rows are on the source's clock, and a span read back out of the file is an offset from the picture it rides on, against presentation times an encode with B-frames does not put in coding order. (ffrwd-index numbers its own rows from one and weave numbers the file's from zero, which is why the space ids differ between the two halves and why find looks a space up rather than naming a number.)

Building

For a contributor with the checkout. An installed copy of the package needs none of this: the modules travel in the archive.

cargo build --target wasm32-wasip2 --release
cargo test

Every module is a node written with ffrwd-node, which carries the world it is built against, and common/ is the wasi:nn glue the four share. embed and embed_clip also export values, on bindings of their own built from wit/av.wit, a copy of the same world. clips-gpu builds clips' source with its gpu feature on, as clips_gpu.wasm, over the copy of the sidecar's ffrwd:gpu wit in clips/wit-gpu/.

The X-CLIP ONNX export under build/xclip is scripts/export_xclip.py's output, pinned to the revision the manifest names.

Checking

sh scripts/check.sh

ffrwd.json's test command, so ffrwd publish runs it too. It generates an eight-second fixture with lavfi, silent and with a noise track, compiles every recipe, then describes and searches both, checking the pictures against the source's own and that the file with sound declares all three spaces. The two compile checks load no model: nothing in describe.sql or describe-video.sql runs while the query compiles, which is what makes them checkable on a machine with an empty model cache. The find recipes embed their prompt at compile time and read a file that has records in it, so they need the towers and a described fixture, and the script makes one.

License

Apache-2.0.