Introduction: Subtitles Are Out Of Sync FIX
A maddening subtitle issue frustrates editors and movie lovers: subtitles start perfectly synced but gradually drift, leaving them several seconds behind by the end. This is almost always due to a frame-rate mismatch between the text and video files.
If you are struggling with subtitles out of sync after a frame rate change, you are dealing with a mathematical speed difference that a simple time shift cannot fix.
This guide provides a deep dive into the mechanics of FPS conversion and offers precise, step-by-step solutions to perfectly realign your captions.
What is FPS (Frames Per Second)?
Movies are just a series of still images, called frames, played rapidly to create the illusion of motion; the speed at which these images, or frames, are shown is called the “Frame Rate,” usually measured in Frames Per Second (FPS).
Standard cinema plays at 24 FPS (24 individual images per second), American TV (NTSC) often uses 23.976 or 29.97 FPS (slightly different image counts per second), and European TV (PAL) uses 25 FPS (25 images per second).
Subtitle files have Timestamps based on a specific frame rate.
If your video player runs at a different speed than the subtitle’s intended frame rate, timing will slip noticeably over time.
The Linear Drift Effect
Unlike a standard delay, where every line is late by the same amount, frame rate issues cause “Linear Drift” or progressive desync.
This means the subtitles might be perfect at 00:00:00, but by 01:00:00, they are 2.5 seconds late.
A 25 FPS video runs 4% faster than a 24 FPS video, causing several minutes of subtitle drift over a two-hour film unless timestamps are adjusted.
Identifying the Source and Target FPS
To correct this, identify the subtitle’s original frame rate (Source) and your video’s frame rate (Target).
Checking Video FPS
Finding the frame rate of your video file is easy, as most modern players display this information clearly.
Open your video file in a player like VLC Media Player. Go to Tools > Codec Information (or press Ctrl + J).
Look for the “Frame rate” field. You will likely see a number like 23.976215 or 25.000000. This is your Target FPS, the speed at which the video is currently running and the speed your subtitles must match.
Deducing the Subtitle FPS
Finding the frame rate the Subtitle File was originally intended for is trickier, as .srt files are just text files with timestamps (each line contains the show/hide time) and do not contain metadata (data that describes file information, such as FPS).
Usually, you have to guess based on the progressive desync behaviour.
If the subtitles appear before the audio (too fast), the subtitle was likely made for a slower frame rate (like 23.976) but is being played at a faster frame rate (like 25).
Conversely, if the subtitles appear after the audio (too slow), they were likely made for 25 FPS but are being played at 23.976 FPS.
Using Subtitle Edit to Change Frame Rate
The most reliable tool for fixing this issue is Subtitle Edit, which has a dedicated calculator for handling these exact conversions.
The “Change Frame Rate” Tool
This feature does the math for you, instantly converting every timestamp to the new speed.
Load your subtitle file into Subtitle Edit. Go to Synchronisation> Change frame rate.
You will see two dropdown menus: “From” and “To.” If you know your subtitles are from a PAL source (25 FPS) and your video is NTSC (23.976 FPS), select 25 in “From” and 23.976 in “To.”
Click “OK,” and the software will instantly apply subtitle FPS conversion to the entire file.
Handling 23.976 vs 24 FPS
One of the most common and annoying issues is the difference between “True Cinema” (24.00) and “NTSC Cinema” (23.976).
Though small (0.1%), the 23.976 vs. 24 FPS difference can cause up to 7 seconds of drift during a 2-hour movie.
If your subtitles are slightly off, convert from 23.976 to 24, or the reverse. This small stretch often fixes Blu-ray rips using the exact 24.000 FPS.
Alternative Method: Visual Point Sync
If you don’t know the frame rates involved, you can skip the numbers entirely and use the “Point Sync” method to visually stretch the subtitles.
Defining Start and End Points
This method anchors the first and last dialogue lines, allowing the software to calculate the necessary adjustment.
Open your video and subtitle in Subtitle Edit. Find the very first line of spoken dialogue and note the exact time it happens.
Then, scrub to the very end of the movie and find the last line. Note that time as well. These two anchors let you fix subtitle drift without knowing whether the video is PAL or NTSC.
Calculating the Ratio Automatically
Go to Synchronisation> Point sync via other subtitle… (or just Point Sync).
Select the first line and enter your manually observed start time. Select the last line and enter the observed end time.
When you hit “Apply,” Subtitle Edit calculates the linear drift ratio and applies it to every line in between.
This effectively adjusts the subtitle frame rate to match the video’s frame rate, regardless of the actual FPS.
The “PAL Speedup” Phenomenon
A specific historical quirk in European television conversion often causes significant sync issues for older movies.
What is PAL Speedup?
When movies shot on film (24 FPS) were transferred to European TV (25 FPS), broadcasters often just played the film faster rather than adding extra frames.
This results in the audio being higher-pitched and the movie ending sooner.
If you download subtitles from a DVD rip (often PAL) and try to use them with a Blu-ray rip (often original 24 FPS), you will experience a significant desync.
A PAL-to-NTSC subtitle conversion (25 -> 23.976) is required to slow subtitles to match the original film speed.
Adjusting for Audio Pitch
While Subtitle Edit fixes the text, be aware that the video itself may change if you edit the media file.
If you are a video editor trying to sync subtitles automatically, remember that if the video has been “PAL sped up,” the timestamps will differ.
Only edit subtitle timestamps not the video frame rate, which is complex and risky.
Online Tools vs. Desktop Software
If you cannot install software, there are web-based alternatives, though they come with limitations regarding precision.
Web-based FPS Converters
Several websites allow you to Upload/Edit an .srt file, select an input/output FPS, and download the result.
Sites like “Subtitle Tools” or “GoTranskript” offer simple online subtitle frame rate converters.
These are convenient for quick fixes on public computers. However, they often lack waveform visualisation, so you have to guess the “Source” FPS.
Why Desktop Software is Better
Desktop tools like Subtitle Edit or Aegisub offer real-time verification using the video file.
With desktop software, you can apply the conversion and immediately press “Play” to verify that the sync subtitles with a different frame rate fix worked.
If the sync is off, you can easily undo and retry different settings. Online tools require slower upload/download/test cycles.
Troubleshooting Common Conversion Errors
Sometimes, even after changing the frame rate, the subtitles are still not quite right. Here is why that happens.
Over-correcting (Speed vs. Delay)
It is possible to have both a frame rate mismatch and a standard time delay.
You may need to convert subtitle FPS and shift all timestamps to fix drift and any time delays.
First, fix frame rate drift with the stretch/convert tools. Once the gap between the first and last lines is correct, use the Delay tool to shift the block into place.
Dealing with Dropped Frames
Sometimes a video conversion goes wrong, and the video file drops frames (removes some images to adjust the speed) or has variable frame rates (VFR), meaning the number of frames per second changes during playback.
Standard conversions won’t work for VFR videos; they require multiple sync points to handle varying speeds.
In this scenario, the only robust fix for progressive desync is to use the “Visual Sync” window in Subtitle Edit and create multiple sync points throughout the video to account for fluctuating speed.
Preventing Future Sync Issues
A few best practices can save you from having to do this math every time you watch a movie.
Matching Filenames to ReleasWhen downloading subtitles, match the release group name (like “YIFY” or “SPARKS”) to your video.G”).
Different groups often use different video sources (Blu-ray vs. WEB-DL). Using subtitles matching your video group usually gives perfect sync—no conversion needed.
Checking Metadata
Before downloading, check the metadata on the subtitle website.
Sites like OpenSubtitles usually list the FPS next to the download button. If FPS numbers match between your video and the subtitle file, no conversion is needed. If not, convert after downloading.ing.
Frequently Asked Questions (FAQ)
How do I know if my subtitles are 23.976 or 25 FPS?
If you don’t know the source FPS, use the trial-and-error method. If the subtitles lag behind the audio, the subtitle FPS is likely lower than the video FPS (e.g., Subtitle is 23.976, Video is 25). If they get earlier, the subtitle FPS is higher (e.g., Subtitle is 25, Video is 23.976).
Can I fix frame rate drift without changing the FPS?
Yes, by using “Point Sync.” You don’t need to know the FPS numbers. You simply point to where the first line starts and where the last line ends, and the software calculates the necessary “stretch” percentage automatically to fix subtitle drift.
Why are my subtitles still out of sync after converting FPS?
You likely have a “Constant Delay” in addition to the drift. After converting FPS, check the first line. If it is 3 seconds late, apply a -3-second delay to the whole file. The FPS conversion fixed the speed; the delay fixes the starting position.
What is the difference between 23.976 and 23.97?
They are usually the same thing. 23.976 is the precise number, while 23.97 or 23.98 are often just rounded abbreviations used in file names. However, “24.000” is distinct and different from 23.976, and mixing them causes sync issues.
Does changing the frame rate affect subtitle text?
No. Changing the frame rate only alters the timestamps (Start Time and End Time). The actual text content, formatting, and styling remain exactly the same during a subtitle time stretch operation.
Why do the subtitles on a TV show DVD not match those on the Blu-ray?
TV DVDs (especially in Europe) are often sped up to 25 FPS (PAL). Blu-rays are usually 24 FPS (Original). You almost always need to convert 25 -> 24 when moving subtitles from a DVD source to a High-Def rip.
Can I use Notepad to change the frame rate?
No. You cannot simply “edit” the frame rate in a text editor because every single timestamp needs to be recalculated mathematically. You need dedicated software like Subtitle Edit to perform this automated subtitle synchronisation math.
What is “Variable Frame Rate” (VFR) and how does it affect subtitles?
VFR means the video changes speed dynamically (common in phone videos). Subtitles rely on Constant Frame Rate (CFR). If your video is VFR, subtitles will constantly go in and out of sync. You must convert the video to CFR using a tool like Handbrake before syncing subtitles.
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