35
Extracting frames from a video with ffmpeg very slow if not using jpeg
(discuss.tchncs.de)
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
this post was submitted on 14 Jul 2024
35 points (94.9% liked)
Linux
48366 readers
1594 users here now
From Wikipedia, the free encyclopedia
Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
Rules
- Posts must be relevant to operating systems running the Linux kernel. GNU/Linux or otherwise.
- No misinformation
- No NSFW content
- No hate speech, bigotry, etc
Related Communities
Community icon by Alpár-Etele Méder, licensed under CC BY 3.0
founded 5 years ago
MODERATORS
My first thought was similar - there might be some hardware acceleration happening for the jpgs that isn't for the other formats, resulting in a CPU bottleneck. A modern harddrive over USB3.0 should be capable of hundreds of megabits to several gigabits per second. It seems unlikely that's your bottleneck (though you can feel free to share stats and correct the assumption if this is incorrect - if your pngs are in the 40 megabyte range, your 3.5 per second would be pretty taxing).
If you are seeing only 1 CPU core at 100%, perhaps you could split the video clip, and process multiple clips in parallel?
At this point I'm very sure that the drive speed is actually the bottleneck. I'm not sure why it's so slow tho. Splitting it is an interesting idea, maybe it's also possible to tell ffmpeg to only extract every 6th frame and start at a different frame for each of the 6 cores.
Coming back to this, what you said at the end was really interesting. I could manually split up the file and run the frame extract script for each one at the same time but do you know if it's possible to automate this? Or even better, run each instance of ffmpeg on the same video file and just extract every nth frame, like I said in my earlier reply?
If your drive is the bottleneck, this will make things worse. If you want to proceed:
You're already using ffmpeg to get the sequence of frames, correct? You can add the
-ssand-tflags to give a start time and a duration. Generate a list of offsets by dividing the length of video by the number of processes you want, and feed them through gnu parallel to your ffmpeg command.