Using ffmpeg to halve frame rate

[Nick Payne]

On 16/04/2018 2:18 AM, RS wrote:
> A couple of years ago there were problems with HLS and there was
> speculation that we might have 50 fps HVFhd and DVFhd as the only HD
> modes.  At that time I wondered if it would be feasible to drop every
> other frame to reduce the frame rte to 25 fps.  I thought because of
> the H.264 delta encoding it would probably mean transcoding and that
> it would be too slow.
>
> On a 42" screen for the programmes that I usually watch I cannot see
> any difference between a HD picture at 50 fps and one at 25 fps, so 50
> fps for me is just a waste of bandwidth and storage space, so I have
> been looking at it again.

I experimented a while ago with running some GiP downloads through
Handbrake to convert the video to the x265 codec. That reduced the file
size to about 1/3 of the original download, with no subjective
difference in video quality that I could see when viewing on our TV. A
one hour 1280x720 25fps program that downloads as a 1Gb file was reduced
in size to ~350Mb. On my PC, the re-encode runs at about 50fps for
1280x720, so ~2x real time for 25fps and ~real time for 50fps. For
smaller video dimension such as 960x540, the re-encode speed was around
85-90FPS.

Nick