ffmpeg surpressing video length even though im not

Question

So I run script which creates screenshots of various videos and save them in given folders. Script is checking how long is video and saves few random frames from within that range. For some videos however it doesn't wokr as intended. For example I have 12 minutes and 30 second long video, which is 750 seconds, so I run this:

ffmpeg -ss 700 -i <input> -vframes 1 -q:v 2 <output>

and it throws errors at me like that:

Output file is empty, nothing was encoded (check -ss / -t / -frames parameters if used)

If I put -ss 650 or less instead it works fine. If I'm correct it should work up to 750, because that's how long the video is, please correct me if I'm wrong. But at this point I don't know how to set my script to make it not produce errors like this.