Extract X Frames From Specific Times to JPG Files

https://ffmpeg-by-example.s3.amazonaws.com/extract-frames-at-time.jpg

The following will take a given input video (e.g. bunny.mp4) and by using the select filter, will only let frames at a specific time (or any valid Expression) pass through.

Since ffmpeg is designed to process an input media file(s) in a frame-by-frame basis. By default, the output of a filter chain will be the same frame rate as the input. This is defined as ‘presentation timestamp’ or PTS in short.

To override this, we need to modify the PTS of the output using the setpts filter.

Without it, when the select condition is met, the frame will pass through. However, when the condition is false and in the lack of any frame data to fill into the needed output frame rate, ffmpeg will repeat the last known frame.

To fix that, we want to limit the PTS to the number of unique frames generated by the select filter. The expression N / FRAME_RATE / TB will do exactly that.

To generate jpg output files, I follow the same principles of the ‘Conver Video File to jpeg Images’ example.

by Elad Gariany <elad@gariany.com>
Updated on: June 23, 2022
tags: #extract-thumbnails #video-extract

ffmpeg -i video.mp4 -vf "select=(eq(22.0\,t))+(eq(32.0\,t))+(eq(84.0\,t))+(eq(98.0\,t))+(eq(120.0\,t)),setpts=N/FRAME_RATE/TB" -f image2 output/%03d.jpeg

2 comments

Anonymous

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tordenfleskcommented3 months ago

If you only need a single image from a bunch of files and you don't want to spend ~5 minutes per image:

ffmpeg -hide_banner -loglevel error -n -ss %num% -i "%%~f" -frames:v 1 -an "%out_path%%%~nf.png"

eladgcommented3 months ago

You example indeed works and I use it literally daily(!), but it does not solve the described problem (extracting multiple frames 😄).

The only reason you will need to 'spend ~5 minutes per image' is because of seeking to the right time on a large file. Your solution solves it by putting the -ss time ahead of the input.

On a project I worked on last week, I needed to extract specific frame numbers from a file - and I did not know at what specific time they are going to play. I used the "eq(n\\,33),eq(n\\,44),eq(n\\,55)" expression to grab the 33, 44 and 55 frames.

Question @tordenflesk : what are all these % symbols? is that PowerShell or something?