How to extract frames from a video using ffmpeg?

Question

Basically I want to extract all frames from the video where the images will be resized to be 720p. All of this I know how to do. But for testing I want to extract every Nth frame. So every 30th image from a 30FPS video or every 10th image, etc. How can I do that?

Also the extracted image filenames should correspond to the frame numbers so not sure if the first frame is 0 or 1?

Answer 1

This prints the frame number on the left upper corner of each frame output and selects only 1 frame every 30 frames:

ffmpeg -reinit_filter 0 -i "input.mkv" -vf "drawtext=text='%{n}':start_number=1:fontcolor=white:bordercolor=black:borderw=3:fontsize=200,select='not(mod(n,30))',scale=-1:720" -fps_mode vfr -y "IMG_Folder\%6d.jpg"

If you want the counter to start at 0 then 30,60,90 instead of 1,31,61,91 remove the startnumber part.

In Windows you can use something like this to do this to all videos inside a folder and save the pictures in a folder same name as video:

for %a in (*.mp4 *.mkv) do if not exist "%~na" md "%~na"& ffmpeg -reinit_filter 0 -i "%~a" -vf "drawtext=text='%{n}':fontcolor=white:bordercolor=black:borderw=3:fontsize=200,select='not(mod(n,30))',scale=-1:720" -fps_mode vfr -y "%~na\%6d.jpg"

Answer 2

At it's most simple, extract single image from frame of video:

ffmpeg -i video.mp4 -ss HH:MM:SS -vframes 1 image.jpg

#!/bin/bash

file="$1"
name="${file%.*}"

# Extract the first frame
ffmpeg -hide_banner -i "$file" -vf "select=eq(n\,0)" -vsync vfr "$name-first_frame.jpg"

# Set the frame interval
frame_interval=30

# Calculate digits required for frame numbering
total=$(ffmpeg -i "$file" -map 0:v:0 -c copy -f null -y /dev/null 2>&1 | grep -Eo 'frame= *[0-9]+' | grep -Eo '[0-9]+' | tail -1)
digits=${#total}

# Extract every nth frame and rename to include actual frame number
ffmpeg -hide_banner -i "$file" -vf "select='not(mod(n\,$frame_interval))',showinfo" -vsync vfr temp_%0${digits}d.jpg 2>&1 | grep 'pts_time' | awk -v name="$name" -v digits="$digits" -F'|' '{ 
    split($5, a, "="); 
    split($8, b, "="); 
    printf "mv temp_%0" digits "d.jpg " name "-frame_%0" digits "d.jpg\n", b[2], b[2]*30 
}' | bash

# Remove temporary files
rm temp_*.jpg

exit 0

Save as: frame_extract.sh
Change mode executable: chmod +x frame_extract.sh
Usage: ./frame_extract.sh input_file.mkv

---

# Define the file path as a parameter
param(
    [Parameter(Mandatory=$true)]
    [string]$FilePath
)

# Get the file name without extension
$name = [System.IO.Path]::GetFileNameWithoutExtension($FilePath)

# Extract the first frame
& ffmpeg -hide_banner -i $FilePath -vf "select=eq(n\,0)" -vsync vfr "$name-first_frame.jpg"

# Set the frame interval
$frameInterval = 30

# Calculate digits required for frame numbering with zero padding
$totalFramesOutput = & ffmpeg -i $FilePath -hide_banner -map 0:v:0 -c copy -f null - 2>&1
$totalFrames = ($totalFramesOutput | Select-String -Pattern 'frame=\s*[0-9]+' | ForEach-Object { $_.Matches } | ForEach-Object { $_.Value.TrimStart("frame=") } | Select-Object -Last 1)
$digits = $totalFrames.Length

# Extract every nth frame and rename to include actual frame number
$output = & ffmpeg -hide_banner -i $FilePath -vf "select='not(mod(n\,$frameInterval))',showinfo" -vsync vfr "temp_%0${digits}d.jpg" 2>&1
$output | Select-String -Pattern 'pts_time' | ForEach-Object {
    if ($_ -match 'pts_time:(\d+)') {
        $frameNumber = [int]($matches[1] * $frameInterval)
        $paddedFrameNumber = $frameNumber.ToString("D$digits")
        $tempFileName = "temp_" + $frameNumber.ToString("D$digits") + ".jpg"
        $newFileName = "$name-frame_$paddedFrameNumber.jpg"
        Rename-Item -Path $tempFileName -NewName $newFileName
    }
}

# Remove temporary files
Remove-Item "temp_*.jpg"

I'm not the greatest at PowerShell, but this should be close.
I have no way to test it, but it should help. (Hopefully!)

---

Added logic to grab the first frame.
Output filename uses frame count, not sequential numbers.