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feat(ffmpeg): add open, read, write and close for chunked file access - #75
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📝 SummarySummary by CodeRabbit
WalkthroughThe FFmpeg API adds ChangesChunked File I/O
Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Feature Sequence Diagram(s)sequenceDiagram
participant FFmpeg
participant Worker
participant FS
FFmpeg->>Worker: Send OPEN, READ, WRITE, or CLOSE request
Worker->>FS: Perform descriptor operation
FS-->>Worker: Return descriptor, bytes, count, or close result
Worker-->>FFmpeg: Resolve request with result
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This PR adds chunked file access (open, read, write, close) to the FFmpeg class, backed by Emscripten's FS API. The implementation adds message types and handlers in both browser and Node workers, exposes the methods on the FFmpeg class with transfer semantics matching writeFile(), and includes tests for chunked write/read, position handling, closed descriptor rejection, and the transfer option. The types package declares the new FS surface. The only known gap is that a closed/unknown descriptor rejects with the raw Emscripten error text rather than a mapped EBADF message, which the PR description acknowledges as noticed but not fixed.
review-bot, model nvidia/nemotron-3-ultra-550b-a55b:free, verdict approve
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Actionable comments posted: 3
- 🪄 Fix CodeRabbit comments on this PR
🤖 Prompt to fix review comments
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only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @packages/ffmpeg/src/classes.ts:
- Around line 415-417: Update the `read` and `write` API documentation in
`classes.ts` and the usage guide to distinguish positioned from unpositioned
operations: positioned reads leave the current offset unchanged, and positioned
writes do not advance it by bytes written. Document that append-mode descriptors
are moved to EOF by Emscripten before a positioned write; preserve the existing
unpositioned offset behavior.
Review comments at @packages/ffmpeg/src/worker.ts:
- Line 159: Update the read paths in both workers, including the `FFmpeg.read()`
length handling, to reject requests exceeding a documented per-read limit before
allocating the buffer or checking the descriptor. Keep support for larger reads
by requiring callers to split them across calls.
- Line 167: Update the read result in both workers so full reads return the
existing buffer when count equals length, while short reads continue slicing to
exclude unread bytes.
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📒 Files selected for processing (10)
CHANGELOG.mdapps/website/docs/getting-started/usage.mdpackages/ffmpeg/src/classes.tspackages/ffmpeg/src/const.tspackages/ffmpeg/src/types.tspackages/ffmpeg/src/worker-node-entry.mtspackages/ffmpeg/src/worker.tspackages/types/types/index.d.tstests/ffmpeg-node.test.mjstests/ffmpeg.test.js
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- GitHub Check: build-preset (web, st)
- GitHub Check: build-preset (decode, st)
- GitHub Check: build-preset (decode, mt)
- GitHub Check: build-preset (web, mt)
- GitHub Check: js
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apps/website/docs/getting-started/usage.md
[locale-violation] ~468-~468: In American English, ‘afterward’ is the preferred variant. ‘Afterwards’ is more commonly used in British English and other dialects.
Context: ...(fd)` releases the descriptor. Using it afterwards rejects. The data still lives in the i...
(AFTERWARDS_US)
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This PR adds chunked file access (open, read, write, close) to the FFmpeg class, backed by Emscripten's FS API in both browser and Node workers. The implementation mirrors writeFile's transfer semantics, includes tests for chunked I/O, position handling, closed-descriptor rejection, and the transfer option. Error handling for invalid descriptors relies on Emscripten's getStreamChecked throwing, which the worker's existing try/catch should catch and propagate.
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This PR adds chunked file access (open, read, write, close) to the FFmpeg WASM library, allowing large files to be read/written in chunks via file descriptors. The implementation adds worker message handlers for OPEN, READ, WRITE, CLOSE in both browser and Node.js workers, using Emscripten's existing FS API. Public methods are added to the FFmpeg class with proper transfer semantics for write(). Tests cover chunked write/read, position/length handling, closed descriptor rejection, and transfer behavior. Documentation and types are updated.
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@coderabbitai all three threads are addressed in 01a6a15. Please review again. |
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The PR adds open(), read(), write(), and close() methods to the FFmpeg class for chunked file access via file descriptors. It updates the message types, worker handlers, TypeScript definitions, documentation, and adds tests. The implementation uses the existing Emscripten FS API and appears correct based on the diff.
review-bot, model nvidia/nemotron-3-super-120b-a12b:free, verdict approve
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This PR adds chunked file access (open, read, write, close) to the FFmpeg WASM wrapper, backporting upstream ffmpegwasm#984. The implementation adds worker message handlers in both browser and Node.js workers that delegate to Emscripten's FS.open/read/write/close/getStreamChecked/fstat. The public API in classes.ts sends messages with proper transferable handling for write(). Tests cover chunked write/read, position/length semantics, closed descriptor rejection, and the transfer option. A known limitation noted in the PR description is that closed descriptors reject with raw Emscripten error text rather than a mapped EBADF message.
Not approved: the check on these comments could not run, so they are unverified.
review-bot, model nvidia/nemotron-3-ultra-550b-a55b:free, verdict comment
| const read = ({ fd, length, position }: FFMessageReadData): Uint8Array => { | ||
| const stream = ffmpeg.FS.getStreamChecked(fd); | ||
| // Allocate no more than the file holds, whatever length asks for. | ||
| const left = ffmpeg.FS.fstat(fd).size - (position ?? stream.position); |
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Optional: The read implementation calculates remaining bytes using position ?? stream.position. This relies on Emscripten's FS.read not updating stream.position when an explicit position is provided (pread semantics). If Emscripten's behavior differs, sequential reads with and without position could desynchronize. Verify against the core's FS.read behavior or add a comment documenting the assumption.
| return count === buffer.length ? buffer : buffer.slice(0, count); | ||
| }; | ||
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| const write = ({ fd, data, position }: FFMessageWriteData): number => |
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Optional: Similarly, write passes position directly to FS.write. The documented behavior states that a write with explicit position should not advance the file offset. This depends on Emscripten's FS.write implementing pwrite semantics. Confirm the core's behavior matches the documented contract.
| ): Promise<number> => | ||
| this.#send( | ||
| { type: FFMessageType.WRITE, data: { fd, data, position } }, | ||
| transfer ? [data.buffer] : [], |
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Optional: Transferring data.buffer transfers the entire underlying ArrayBuffer, not just the Uint8Array view. If callers pass a view into a larger buffer (e.g., new Uint8Array(largeBuffer, offset, length)), the whole buffer becomes unusable. This matches writeFile() behavior but is worth documenting in the method's JSDoc for clarity.
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@coderabbitai all threads are resolved. Please approve. |
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✅ Action performedComments resolved and changes approved. |
What and why
Adds `open()`, `read()`, `write()` and `close()` to `FFmpeg`, so a large file can be written to or read from the core's file system in chunks through a file descriptor instead of one array. Backport of upstream ffmpegwasm#984.
This does not stream input into the core. The data lands in MEMFS and `exec()` still reads from there.
Tests
Mocha tests for chunked write then read back, read with length and position, closed descriptor rejecting, and the transfer option, in `tests/ffmpeg.test.js` (browser) and `tests/ffmpeg-node.test.mjs`.
Run locally: `pnpm lint`, the ffmpeg package build, and the new Node tests (st core, using an existing local debug build of the core copied in temporarily). Not run locally: the browser tests and the mt core.
Noticed, not fixed
Review
review-bot approved 01a6a15. On the head (0a4ac8e, docs wording only) its verification step failed, so a Sonnet reviewer read the head instead and found nothing blocking. It checked the read clamp against Emscripten 6.0.10's MEMFS and WORKERFS, the transfer handling, and the append-mode docs. CodeRabbit's three threads are resolved and it approved.