@Gyan is correct. You can reverse a video using ffmegs built in reverse video filter:
ffmpeg -i video.mp4 -vf reverse video_reversed.mp4
However this is incredibly memory intensive. I wont go into details but it has to do with the video is saved in a compressed format. To reverse it, it needs basically load each frame of the video into memory.
Therefor for any reasonably sized video (> 10 minutes) you are going to have a tough time using the above command. Thus to complete @Gyan's answer. Here is how to segment the video, reverse each part, and then concatenate them again.
You can first segment a video into 300 second chunks using:
ffmpeg -i video.mp4 -map 0 -c copy -f segment -segment_time 300 -reset_timestamps 1 video_%03d.mp4
This will output a bunch of video files named video_000.mp4, video_001.mp4 etc. Next you need to reverse each of these segments. You can either do that manually using the original reverse command, or you can use the loop provided below.
NOTE: Make sure you remove the original video video.mp4 from the folder before using the loop below (otherwise you are back to the start).
Alternatively for long videos you might want to use a loop. This loop looks for all mp4 files in the current directory and reverses each of them:
To reverse only the video but not the audio:
for f in *.mp4; do
ffmpeg -i $f -vf reverse ${f/.mp4/_reversed.mp4}
done
To reverse the video and audio:
for f in *.mp4; do
ffmpeg -i $f -vf reverse -af areverse ${f/.mp4/_reversed.mp4}
done
You will now have a set of reversed segments med video_000_reversed.mp4, video_001_reversed.mp4 etc. The final command concatenates them into a single video. To do that we need a text file with all the files we want to concatenate. You can automatically create this text file using the following:
for f in ./SegmentedVideos/*_reversed.mp4; do
echo file \'$f\' > tmp.txt
cat fileList.txt >> tmp.txt
rm fileList.txt
mv tmp.txt fileList.txt
done
At this point you should have a text file fileList.txt that contains the video files in reverse order like this:
file './video_XXX_reversed.mp4'
...
file './video_001_reversed.mp4'
file './video_000_reversed.mp4'
Then all we need to do is concatenate everything:
ffmpeg -f concat -safe 0 -i fileList.txt -c copy final_revered_video.mp4
