FFmpeg Frame Rate ? -r vs fps Filter Guide

Want to convert 60fps footage to 30fps for the web, get a cinematic 24fps feel, or create a timelapse? FFmpeg’s fps filter handles all of these in a single command. Understanding the difference between -vf fps and -r lets you get stable results even with variable frame rate source material. Time to complete: 10 minutes.

Tested with: FFmpeg 6.1 (ubuntu-latest / GitHub Actions CI-validated)

What You Will Learn

1. How to check frame rate with ffprobe
2. The -r option vs the fps filter — differences and when to use each
3. Decreasing frame rate (60 → 30fps, etc.)
4. Increasing frame rate (24 → 60fps)
5. Commands for common use cases
6. Timelapse creation
7. Five common errors and fixes
8. Five frequently asked questions

First: Check the Current Frame Rate

Before converting, check the source file’s frame rate.

ffprobe -v error -select_streams v:0 \
  -show_entries stream=r_frame_rate,avg_frame_rate \
  -of default=noprint_wrappers=1 input.mp4

Example output:

r_frame_rate=60000/1001
avg_frame_rate=60000/1001

For variable frame rate (VFR) video these values may differ. 60000/1001 ≈ 59.94fps (NTSC standard).

Command Examples

1. Decrease Frame Rate (fps filter — recommended)

# 60fps → 30fps (web delivery, social media)
ffmpeg -i input.mp4 -vf fps=30 -c:v libx264 -crf 23 -c:a copy output.mp4

# 29.97fps → 25fps (PAL standard, Europe)
ffmpeg -i input.mp4 -vf fps=25 -c:v libx264 -crf 23 -c:a copy output.mp4

# 30fps → 24fps (cinematic look)
ffmpeg -i input.mp4 -vf fps=24 -c:v libx264 -crf 23 -c:a copy output.mp4

• fps=N — target frame rate; drops excess frames based on timestamps
• -c:a copy — copy audio without re-encoding (fast, lossless)

2. Use the -r Option (for simple cases)

# Set output frame rate to 30fps
ffmpeg -i input.mp4 -r 30 -c:v libx264 -crf 23 -c:a copy output.mp4

-r duplicates or drops frames immediately before encoding. Fine for simple cases, but the fps filter is more stable with VFR source material.

3. Increase Frame Rate (frame duplication)

# 24fps → 60fps (frame duplication)
ffmpeg -i input.mp4 -vf fps=60 -c:v libx264 -crf 23 -c:a copy output.mp4

When increasing frame rate, the fps filter achieves the target by duplicating existing frames — no new intermediate frames are generated. True motion interpolation requires the minterpolate filter.

4. Timelapse: Extract at 1fps

# Extract one frame per second — creates ultra-low-frame-rate video
ffmpeg -i input.mp4 -vf fps=1 -an -c:v libx264 -crf 23 output_timelapse.mp4

• -an — remove audio (audio would be out of sync with the shortened video)

5. Build Timelapse from Image Sequence

ffmpeg -framerate 1 -i img%03d.png -c:v libx264 -r 30 -pix_fmt yuv420p output.mp4

• -framerate 1 — read input images at 1fps (1 image = 1 second)
• -r 30 — output at 30fps (each image becomes 30 frames)
• -pix_fmt yuv420p — pixel format for broad compatibility

6. Batch Convert All Videos in a Folder to 30fps

for f in *.mp4; do
  ffmpeg -i "$f" -vf fps=30 -c:v libx264 -crf 23 -c:a copy "30fps_${f}" -y
done

-r Option vs fps Filter Comparison

Recommendation: When in doubt, use -vf fps=N. It’s especially effective for VFR sources (smartphone footage, OBS recordings, etc.).

Common Frame Rate Reference

Option Reference

Troubleshooting

Problem 1: Audio Is Out of Sync After Conversion

Symptom: Video and audio timing is misaligned after conversion
Cause: Converting VFR source with -r can cause audio timestamp drift when frames are dropped or duplicated
Fix:

# Use fps filter instead — more stable
ffmpeg -i input.mp4 -vf fps=30 -c:v libx264 -crf 23 -c:a copy output.mp4

Problem 2: Timelapse Has Audio That’s Too Long

Symptom: Video is short but audio runs for the original duration
Cause: fps=1 shortens the video but leaves audio unchanged
Fix: Remove audio for timelapse:

ffmpeg -i input.mp4 -vf fps=1 -an -c:v libx264 -crf 23 output.mp4

Problem 3: No such encoder libx264

Cause: FFmpeg was built without libx264 support
Fix: Install the full-featured FFmpeg:

sudo apt install ffmpeg        # Ubuntu/Debian
brew install ffmpeg            # macOS

Problem 4: Output Frame Rate Didn’t Change

Cause: -r was placed on the input side (before -i) instead of the output side
Fix: Always place frame rate options after -i:

# Wrong (input-side -r)
ffmpeg -r 30 -i input.mp4 output.mp4

# Correct (output-side)
ffmpeg -i input.mp4 -vf fps=30 -c:v libx264 -crf 23 output.mp4

Problem 5: Image Sequence Fails to Load (pts has no value)

Cause: Missing -framerate flag, or the filename pattern doesn’t match
Fix:

# Check file naming pattern first
ls img*.png | head -3
# Example: img001.png img002.png img003.png → use %03d

ffmpeg -framerate 24 -i img%03d.png -c:v libx264 -pix_fmt yuv420p output.mp4

FAQ

Q1. Should I use -r or -vf fps=N?
A. Use -vf fps=N when in doubt. It references timestamps and produces stable results especially with VFR sources like smartphone or OBS recordings. Use -r for simple, constant frame rate sources.

Q2. Does increasing the frame rate make motion smoother?
A. No — the fps filter duplicates existing frames. Motion smoothness stays the same as the original. For genuine interpolation (generating new in-between frames via motion estimation), use the minterpolate filter — but it’s significantly slower.

Q3. How do I verify the output frame rate after conversion?

ffprobe -v error -select_streams v:0 \
  -show_entries stream=avg_frame_rate \
  -of default=noprint_wrappers=1 output.mp4

Q4. Can I keep audio in a timelapse?
A. Technically yes, but the audio won’t sync with the shortened video. The practical approach is to remove audio (-an) and add background music separately in post-production.

Q5. Can I specify fractional frame rates like 29.97fps?
A. Yes — use the rational form:

# 29.97fps (NTSC)
ffmpeg -i input.mp4 -vf fps=30000/1001 -c:v libx264 -crf 23 output.mp4

Related Articles

• Scale and Resize Video — scale Filter Guide
• Create Slideshow and Timelapse Videos
• Video Compression Complete Guide — CRF, Bitrate, and Presets
• FFmpeg Command Basic Syntax — Inputs, Filters, and Outputs

Tested with: ffmpeg 6.1.1 / Ubuntu 24.04 (GitHub Actions runner)
Primary sources: ffmpeg.org/ffmpeg.html / ffmpeg.org/ffmpeg-filters.html / ffmpeg.org/ffmpeg-codecs.html