RuntimeError: memory access out of bounds is a WebAssembly runtime error, not proof that your computer has run out of physical RAM. In ffmpeg.wasm, reports associate it with different situations—including larger frame workloads and repeated jobs—without establishing one shared cause. For slideshow developers, the practical response is to isolate the failing workload and check image orientation separately; only one of the five slideshow gotchas named in the original title could be verified.
What the error does—and does not—tell you
The message identifies a failed WebAssembly memory access. By itself, it does not tell you whether the underlying issue is memory pressure, a particular FFmpeg command or codec, a build defect, or how repeated jobs are managed. The error text alone is not a diagnosis, and the reports below do not establish a universal fix or memory threshold.
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For the API and project context, start with the official ffmpeg.wasm documentation and check the documentation that matches the versions of the packages you use. The available documentation does not establish a universal memory limit or a version-specific fix for this exception.
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Three reported failure patterns to distinguish
These issue reports are examples from individual setups, not proof that all out-of-bounds errors share a root cause. Their value is in showing which variables are worth separating during diagnosis.
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Larger frame and snapshot workloads
In ffmpeg.wasm issue #673, opened January 16, 2024, a developer reported that a Next.js and TypeScript workflow—reading a video, extracting frames, drawing rectangles, and producing PNG snapshots—worked with a smaller amount of data but failed as the workload increased. The report does not include a maintainer-confirmed cause or resolution. It shows a workload-size correlation in that user’s setup, not a general threshold.
Many sequential thumbnail jobs
Issue #704, opened March 13, 2024, describes a thumbnail workflow that reportedly crashed after roughly 60–70 files, with a loop over 80 files used as a reproduction. The reporter suspected worker retention and memory accumulation, but that was the reporter’s explanation, not an established finding. Do not treat those file counts as typical limits.
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A custom build failing on later commands
An Emscripten issue #22400, opened August 19, 2024, describes a custom FFmpeg WebAssembly build that reportedly failed on a second or later command in a session. The report includes build details and a stack trace in cleanup code, but does not prove that repeated-command errors in other builds have the same cause.
How to narrow down your own reproduction
Change one factor at a time. That helps determine whether your failure follows the input workload, the command, or the fact that work is repeated; it does not guarantee a fix.
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- Reduce the case. Try the smallest input, one FFmpeg command, and one output. Save the exact arguments, full FFmpeg log, and browser stack trace.
- Vary the workload. Compare smaller and larger inputs or frame counts. Keep the command and environment the same so you can see whether workload size changes the result.
- Test repetition independently. Run the same command once, then in successive jobs. If only repeated work fails, record how many jobs run and whether the failure is consistent; do not assume a worker leak from the symptom alone.
- Check command and media variables. If size and repetition do not explain the failure, vary the codec or filter combination and input format or dimensions one at a time.
- Record the environment. Include
@ffmpeg/ffmpegand@ffmpeg/coreversions, browser and version, input format and dimensions, and whether you use the stock core package or a custom Emscripten build. These details make a report more useful and can help distinguish a package-specific issue from a custom-build problem. - Audit batch handling. Check filenames and cleanup between jobs. Calling a termination method does not, on its own, establish that every resource has been released; the issue reports do not provide an official lifecycle guarantee.
Increasing RAM or switching to a more powerful computer is not a generally supported fix: the cited reports do not establish that physical memory is the cause. If a reduced reproduction still fails, compare it with the relevant issue tracker and report the exact case rather than inferring a cause from the exception string.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Keep phone photos upright in a slideshow
A separate slideshow problem is image orientation. Phone photos may rely on EXIF metadata to describe rotation. The indexed excerpt for a DEV Community article states that createImageBitmap(file, { imageOrientation: 'from-image' }) applies EXIF rotation. Check that behavior in your target browser and image-decoding pipeline before relying on it as a guaranteed fix.
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The article’s full page could not be verified, so the other four gotchas implied by its title are not reproduced here. There is not enough verified detail to name them without guessing.
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