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Video Speed Changer with Audio Stretch

Change video speed with synchronized audio stretching and explicit output dimensions and frame rate.

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Local files · native first · WASM when needed · no uploads

Files and settings

Editable sample: 12 seconds from the 2009 U.S. inaugural address, marked public domain under U.S. law. Source and license · Steve Jobs at Stanford ↗ · Jensen Huang speeches ↗

Drop local files here. Up to three clips; source size and duration follow this device’s budget above. Source up to 1080p.

Time range
The start is included. Compressed audio can contain codec padding; tiny duration differences are normal.
Output frame
Use even dimensions. Native video: up to 1080p; WASM video: up to 720p, including portrait 720×1280. Frame captures can use up to 1080p.
Video format and quality
Bitrate is a target, not an exact file-size promise. Native supports up to 60 FPS, WASM up to 30 FPS; unsupported settings are rejected rather than silently changed.
Playback speed0.25–4×. Audio is time-stretched with pitch preservation. Exact quality varies with the material.
Audio settings
Opus may require 48 kHz. MP3 at 16/24 kHz is limited to 160 kbps; use 44.1/48 kHz for higher MP3 rates.
Processing method and compatibility

WASM first use loads about 32 MB from this site. Captions and watermarks may load an additional 16 MB local font. Files are never sent for server conversion.

Your video stays on your device

Start with a local file or the attributed speech sample. The preview and actual output appear here.

Supported formats depend on the device. Unsupported or damaged files get an explicit message.

Getting started

Choose the speed, review the expected duration and export a clip with synchronized audio.

Before you use the result

Device-aware sources: 256 MiB–2 GiB per file and 1–4 hours combined, up to three clips, one video and at most one audio track, up to 1080p source. Native long outputs can use local temporary storage; WASM has separate input/output/working-memory budgets and up to 720p/30 FPS. Actual codecs, memory and storage are checked; compression is not guaranteed.

Try an example

A three-second clip at 2× is about 1.5 seconds; confirm the sound still matches the picture.

How it works

Browser-native WebCodecs and Mediabunny are preferred; fixed single-thread FFmpeg WASM operations cover missing codecs and other supported tasks. Inputs and outputs are checked for dimensions, duration and expected tracks; long native results use bounded sample checks and can stream to private local temporary storage. No server conversion or arbitrary commands.

Frequently asked questions

Change video speed with synchronized audio stretching and explicit output dimensions and frame rate.

How do I use Video Speed Changer with Audio Stretch?

Choose the speed, review the expected duration and export a clip with synchronized audio.

Does this tool upload my data?

Inputs and files are processed in your browser. Page-view analytics do not contain your tool input.

What should I check before using the result?

Device-aware sources: 256 MiB–2 GiB per file and 1–4 hours combined, up to three clips, one video and at most one audio track, up to 1080p source. Native long outputs can use local temporary storage; WASM has separate input/output/working-memory budgets and up to 720p/30 FPS. Actual codecs, memory and storage are checked; compression is not guaranteed.

Related tools

Video Trimmer: Cut a Clip LocallyCut a supported local video with a visual timeline and precise start/end controls; export MP4 or WebM with audio preserved.Video Joiner: Merge Clips in OrderPreview and arrange up to three local clips on a visual timeline, then merge with normalized dimensions and frame rate.Video Converter: MP4 and WebM in Your BrowserConvert supported local videos to MP4 or WebM using available native codecs or a single-thread WASM fallback.