Slow Video to 0.5×
Play the video at half speed. The resulting duration is approximately twice the source duration.
Media Tools
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Free Online Tool
Free Video Speed Controller – Speed Up or Slow Down Video
Speed up or slow down MP4, WebM, MOV and other supported videos online. Choose a speed from 0.25× to 4× and process video with synchronized audio in your browser.
Free to Use
No Sign-Up
Browser-Based
Online Tool
Free Video Speed Controller – Speed Up or Slow Down Video
Ready
Change Your Video Speed
Upload a video, choose a playback-speed preset from 0.25× to 4×, then create a slower or faster version with synchronized audio.
0.25× – 4×
Audio Timing
Processed in your browser
Upload Video to Change Speed
Supports MP4, WebM, MOV and other video files that can be decoded by the browser FFmpeg build.
Preview Not Available
Your browser may not be able to preview this format, but FFmpeg may still be able to process it.
Playback Speed
Choose how quickly or slowly the finished video should play.
Selected Mode
Slow Motion Mode
Fast Motion Mode
Normal Speed
Speed Adjusted Successfully!
Preview the adjusted video and download the finished file.
Speed Up or Slow Down Video Online
Change how fast a video plays without manually editing its timeline. CyberTools modifies video timestamps with FFmpeg setpts and adjusts audio tempo with atempo, allowing supported video and audio streams to stay aligned at speeds from 0.25× to 4×.
0.25× to 4× speed
Slow motion
Fast motion
Audio tempo adjustment
FFmpeg setpts
Browser processing
No sign-up
How do I change video speed online?
Upload a supported video, choose one of the available speed presets, and click Apply Speed. CyberTools changes the video timestamps using FFmpeg setpts and adjusts the audio duration with atempo filters. A 0.5× setting makes the video roughly twice as long, while 2× makes it roughly half as long.
Common Video Speed Adjustment Tasks
Playback-speed changes are useful for slow demonstrations, fast tutorials, time-compressed recordings, quick previews and simple speed effects.
Create 0.25× Slow Motion
Stretch playback to one quarter of the original speed for detailed review of movement.
Speed Video Up to 1.5×
Make tutorials, explanations or recordings shorter while keeping motion and audio synchronized.
Create 2× Fast Motion
Play the video at double speed, reducing its approximate playback duration by half.
Create 3× or 4× Fast Motion
Compress long visual sequences into much shorter playback when detailed real-time motion is not required.
Restore Normal 1× Speed
Use the normal-speed preset when you need standard playback timing.
0.25× vs 0.5× vs 1× vs 2× vs 4× Video Speed
The speed multiplier controls how quickly the timeline advances. Lower values extend playback; higher values shorten it.
| Speed | Approximate duration | Typical use | Important consideration |
|---|---|---|---|
| 0.25× | 4× longer | Detailed slow review | Original frames are stretched over more time; new motion detail is not created. |
| 0.5× | 2× longer | Slow motion | Can appear less smooth if the source frame rate is low. |
| 1× | Original duration | Normal playback | No intentional speed change. |
| 1.5× | About 67% of original duration | Faster tutorials or explanations | Speech becomes faster even though tempo processing keeps timing synchronized. |
| 2× | Half the original duration | Fast review | Motion and speech move at double speed. |
| 4× | One quarter of original duration | Strong fast-motion effect | Very fast movement and speech may become difficult to follow. |
How CyberTools Changes Video Playback Speed
The current browser tool re-encodes the processed video so corrected timestamps can be written into the new file. Video timing is controlled with setpts, while audio timing is controlled with one or more atempo filters.
Video File Loaded Into FFmpeg
The selected source file is written to FFmpeg WebAssembly’s browser-side virtual filesystem.
Speed Multiplier Converted to Timing Factor
The tool calculates a timing factor as 1 divided by the selected playback speed.
Video setpts Filter
FFmpeg setpts changes frame presentation timestamps. Faster playback uses a smaller timestamp factor; slower playback uses a larger factor.
Audio atempo Filter
Audio tempo is changed so the soundtrack duration follows the adjusted video duration.
Chained atempo Filters
For speeds outside one atempo filter’s normal 0.5-to-2 range, multiple atempo stages are chained together.
New Video File Created
FFmpeg re-encodes the adjusted media and returns the completed output file for browser preview and download.
What Video Speed Should You Use?
Choose a multiplier based on whether your priority is detailed viewing, natural motion, shorter playback or a strong visual speed effect.
Slower playback gives viewers more time to inspect each captured frame.
Reduces playback speed without stretching the timeline as aggressively as 0.5×.
Uses the source timing without an intentional speed effect.
Shortens playback while usually remaining easier to follow than extreme fast motion.
Cuts approximate duration in half.
Useful when overall visual progression matters more than fine detail.
How Speed Changes Affect Motion, Duration and Quality
Changing playback speed changes timing, not the information originally captured by the camera. Slow playback cannot automatically create genuine intermediate frames that were never recorded.
Slow Motion Does Not Create New Detail
A 30 FPS source slowed to 0.25× still contains the original captured frames. The timeline is stretched, but genuine new motion samples are not reconstructed.
Source FPS Matters
High-frame-rate source footage usually produces smoother slow playback because more original motion samples were captured.
Frame Interpolation Is Different
AI or optical-flow interpolation creates estimated intermediate frames. This speed controller changes timing but does not perform motion interpolation.
Fast Motion Drops Viewing Time
Higher speed multipliers show the same source sequence in less time, making fine details harder to inspect.
Re-encoding Can Affect Quality
The current implementation re-encodes the processed video, so final quality also depends on FFmpeg encoding behavior and the source media.
Extreme Changes Affect Perception
Very slow or very fast playback can make movement or speech feel unnatural even when timing remains synchronized.
Where Is Your Video Processed?
The current CyberTools Video Speed Controller performs its main FFmpeg processing in your browser using WebAssembly.
- The selected source file is written to FFmpeg’s browser-side virtual filesystem during processing.
- Timestamp adjustment, audio tempo filtering and video encoding use your browser and device resources.
- The completed output is read from FFmpeg memory and exposed to the page for preview and download.
- Browser processing remains subject to available RAM, CPU performance, browser limits and source-file size.
What a Browser Video Speed Controller Cannot Do
Playback-speed adjustment is not the same as AI slow-motion generation, frame interpolation or full professional timeline editing.
- Slow playback does not generate genuine missing frames from low-frame-rate source footage.
- The tool does not perform AI frame interpolation or optical-flow motion synthesis.
- Very large or high-resolution videos can exceed browser or device memory limits.
- Unsupported source codecs or containers may fail in the available FFmpeg WebAssembly build.
- Extreme speed multipliers can make speech and motion difficult to follow.
- The current workflow is designed for individual browser conversions rather than large batch-processing jobs.
Video Speed, PTS, FPS, atempo and FFmpeg Explained
These concepts explain what actually changes when video playback becomes slower or faster.
- Playback Speed
- The rate at which the media timeline advances relative to normal 1× playback.
- Speed Multiplier
- A value such as 0.5× or 2× that determines how quickly the adjusted video plays.
- PTS
- Presentation timestamp information that tells a media player when a frame should be displayed.
- setpts
- An FFmpeg video filter used to modify presentation timestamps and therefore change video playback timing.
- atempo
- An FFmpeg audio filter used to change audio tempo so soundtrack duration can follow the adjusted video speed.
- FPS
- Frames per second, representing how many source image frames are captured or displayed each second.
- Frame Interpolation
- A separate process that estimates new intermediate frames between existing frames to create smoother slow motion.
- Codec
- A method used to encode and decode video or audio streams.
- FFmpeg
- A media-processing framework used to decode, filter, re-time and encode audio and video.
- WebAssembly
- Browser technology that allows compiled software such as FFmpeg to run inside a web page.
Video Speed Controller FAQ
Answers about slow motion, fast motion, audio synchronization, FFmpeg timing, browser processing and video quality.
How do I speed up a video online?
Upload a supported video, choose a multiplier above 1× such as 1.5×, 2×, 3× or 4×, then apply the speed. CyberTools changes video presentation timestamps and adjusts audio tempo so the output plays faster.
How do I slow down a video online?
Choose a multiplier below 1× such as 0.75×, 0.5× or 0.25×. Lower multipliers stretch the media timeline, producing longer playback.
What does 0.5× video speed mean?
A 0.5× multiplier plays the timeline at half normal speed. The adjusted video is therefore approximately twice as long as the original.
What does 2× video speed mean?
A 2× multiplier plays the media twice as quickly, making the resulting playback approximately half as long as the source.
Does changing video speed keep audio synchronized?
The current CyberTools implementation changes the video timestamps with setpts and changes audio timing with FFmpeg atempo filters so both streams follow the selected speed.
Does slowing a video create new frames?
No. This tool changes playback timing but does not perform AI or optical-flow frame interpolation. Slowing a low-frame-rate source can therefore appear less smooth than footage originally recorded at a high frame rate.
Does changing playback speed change audio pitch?
The tool uses FFmpeg atempo processing to change audio tempo rather than simply changing raw playback rate. The goal is synchronized duration without the basic chipmunk-style pitch shift associated with naive resampling.
Is my video uploaded to a conversion server?
The current CyberTools workflow performs its main FFmpeg conversion in the browser with WebAssembly. The source file is written to FFmpeg’s browser-side virtual filesystem for processing.
Why can a large video fail when changing speed in the browser?
FFmpeg must decode, filter and re-encode the media while holding working data in browser memory. Large files, high resolution and limited device memory can exceed browser resource limits.
What is the best speed for a video?
There is no universal best multiplier. Use 0.5× or 0.75× for easier inspection, 1.25× or 1.5× for mild acceleration, 2× for quick review, and 3× or 4× when strong time compression matters more than detail.
Change video playback speed online from 0.25× slow motion to 4× fast motion. CyberTools adjusts video timestamps and audio tempo with FFmpeg WebAssembly directly in your browser.
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