Using ffmpeg to halve frame rate

[Nick Payne]

On 16/04/2018 5:21 PM, Steve Dodd wrote:
> On Sun, Apr 15, 2018 at 9:59 PM, Nick Payne <njhp94 at gmail.com> wrote:
>
>> 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.
> Figures - most of the comparison work done on H.265 v. H.264 says you
> should get same subjective quality for half the bitrate.
>
>> 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.
> Do you know what x265 quality setting you used? I'm also experimenting
> now it seems HLSHD is being turned off (series 2 of Salamander has HVF
> only so far).. RF17 seems to be spitting about half the bitrate of the
> BBC h.264 output, and running at ~40fps which I can live with (Core
> i5-6500). Noticeable quality difference still when looking at stills,
> but have tried watching it moving yet..
For re-encoding 1280x720 downloads to x265, on the Video tab in
Handbrake I have the encoder preset at "Faster" and the RF quality at 23.

Nick