ffmpeg - duplicated frames

Question

I'm converting a couple of videos that I have using the following command:

ffmpeg -i input.mp4 -c:v hevc_amf -c:a copy input_h265.mp4

It works, but on some videos I get this warning message:

More than 1000 frames duplicated    4608kB time=00:00:19.07 bitrate=1979.3kbits/s dup=914 drop=0 speed=3.68x
More than 10000 frames duplicated  53760kB time=00:03:28.34 bitrate=2113.8kbits/s dup=9934 drop=0 speed=3.44x
More than 100000 frames duplicated 560128kB time=00:35:52.64 bitrate=2131.6kbits/s dup=99919 drop=0 speed=3.69x

Does that mean that the input video already had those duplicate frames, or it is a problem that the converted one will have? Is it an issue at all? If so, how can I fix or prevent it from happening?

Answer 1

From my personal experience: if you can not see anything unusual in the input video at specified times then most of the time it's not worth fixing as it's not broken.

It can happen when input video has some static images (like some schematics) displayed over some periods of time.

It can also happen when input video is a converted version of lower fps video to higher fps video. For example: the input video has 50 fps but its original in the past had 25 fps so the current input video has every second frame duplicated to reach the needed 50 fps.