Subtitle Speed Adjuster
Stretch or compress subtitle timing by a speed factor. Match subtitles to videos played at different speeds.
Drag & drop your subtitle file here
Drag and drop subtitle files here or click to browse
Key Features
Engineered for video editors and localization teams. Helps enforce common subtitle timing rules and formatting.
Subtitle Speed Adjuster Live Execution Demo
In-Memory Processing
File parsing, mutations, and time shifts for standard tools run in browser memory without sending subtitle files to our servers.
Millisecond Precision
Millisecond-accurate timecode parsing and arithmetic prevent synchronization drift across desktop and web players.
Fault-Tolerant Engine
Automatic multi-encoding detection and syntax sanitization gracefully handle malformed cues and unexpected linebreaks.
Common Use Cases
Real-world scenarios across video post-production, course transcription, and global localization.
PAL Speedup (24 to 25 fps)
A 24 fps film played as 25 fps PAL runs 4.17% faster. Use factor 25/24 to compress subtitle timestamps.
PAL Slowdown (25 to 24 fps)
A 25 fps PAL video played at 24 fps runs 4% slower. Use factor 24/25 to stretch subtitle timestamps.
Slow-Motion Video
For a video slowed to 0.5x, use factor 0.5 so subtitles stretch to match the slowed audio.
Fast-Motion / Timelapse
For a video sped up to 1.25x, 1.5x, or 2x, enter that same factor to compress subtitle timestamps.
How It Works
Streamlined end-to-end processing pipeline engineered for speed and precision.
Upload & Import
Select your subtitle file.
Enter a speed factor
values above 1 compress timing; values below 1 stretch it.
Configuration
Keep the first start time or the last end time fixed while all other timestamps are rescaled.
Choose SRT
VTT, or ASS output, then click Adjust Speed and download the file.
Why Choose AllSubConverter?
Client-Side Privacy
Standard tools run in your browser so standard files are not uploaded to our servers.
Fast Local Parsing
Optimized processing engine parses and converts files directly in your browser.
Generous Batches
Up to 50 MB per file, 200 files or 1 GB total per batch.
Universal Compatibility
Runs in modern browsers across Windows, macOS, Linux, iOS, and Android.
More Subtitle Tools
Frequently Asked Questions
The tool divides each timestamp offset by the factor from the selected anchor. Values above 1 compress timing for faster video; values below 1 stretch timing for slower video.
Yes. Both the start and end of each cue are rescaled relative to the selected anchor, so cue durations change with the video speed.
Free with no registration, no watermarks, and no file uploads.
Use factor 25/24 (about 1.041667) for a 24-to-25 fps speedup. For the reverse, use 24/25 (0.96).
Input: SRT, VTT, ASS, SSA, LRC, SBV, TTML, SCC, STL, SMI, and JSON. Output: SRT, VTT, or ASS.
Yes. Everything runs client-side. No subtitle data is ever sent to a server.
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