widely varying download sizes

[xndr]

GiP can help with reducing output bitrate but this is achieved by using
a custom command for ffmpeg (either on the command line or embedded in
the appropriate preset)

We've found the following ffmpeg flags help considerably:-

-> Reduce frame rate by half using: -r 25

https://trac.ffmpeg.org/wiki/ChangingFrameRate

-> Reduce the output bit rate using combo's of: -b:v -minrate -maxrate
-bufsize

https://trac.ffmpeg.org/wiki/Limiting%20the%20output%20bitrate

The first suggestion will easily result in an appreciable reduction in
output size for a modest hit on encode times.

The second can help further but comes with significant computational
overhead (i.e. time) as well as producing a subjectively better/worse
result. This means some experimentation!

To find out, try ffmpeg on the command line with short stretches of
video (~10-15mins) to see how different material performs - there will
be different results for natural, studio, film, live & CGI material.

How to implement custom ffmpeg command is given in the github wiki.

HTH

On 20/09/2022 16:29, D Martin wrote:
> Hi all.  Neither a newbie nor an expert here, so I feel the need to
> ask all you experts ...
> A few months ago I realised that better resolution video was possible
> by using dashfhd1, than what I'd previously been using.
> It works well and the 1920 x 1080 video is lovely.
> It does take up a lot of space though, and now I'm seeing 2:1 space
> differences between different programs recorded the same way. Three
> examples below ...
>
> PID Type Name Episode Versions Duration Channel Time Added Filename Mode
>
> First this is THE REPAIR SHOP, file explorer shows 1.39GB, 28mins50
> secs, 1920x1080, 6901kbps, 50fps,
> b09wv7ck tv The Repair Shop: Series 2 04. Episode 4 original 1730  BBC
> One 1d 15h ago H:\New_Audio\The_Repair_Shop_Series_2_-_04._Episode_4_b09wv7ck_original.mp4
> dashfhd1
>
> Second this is FAKE OR FORTUNE, file explorer shows 1.67GB,
> 58mins14secs, 1920x1080, 4099kbps, 50fps
> m001c26z tv Fake or Fortune?: Series 10 04. Flemish Old Master
> audiodescribed,original 3540 BBC One 6d 0h ago
> H:\New_Audio\Fake_or_Fortune_Series_10_-_04._Flemish_Old_Master_m001c26z_original.mp4
> dashfhd1
>
> Third this is SAVING LIVES AT SEA, file explorer shows 3.20GB,
> 58mins45secs, 1920x1080, 7790kbps, 50fps
> m001bvr8 tv Saving Lives at Sea: Series 7 03. Caught Out
> audiodescribed,original 3540 BBC Two 3d 21h ago
> H:\New_Audio\Saving_Lives_at_Sea_Series_7_-_03._Caught_Out_m001bvr8_original.mp4
> dashfhd1
>
> So summarising .....
> REPAIR SHOP            1.39GB  29mins 6901kbps
> FAKE OR FORTUNE   1.67GB 58mins 4099kbps
> SAVING LIVES ..         3.20GB 59mins  7790kbps
>
> Clearly the kbps is the critical factor.  So I guess this is quite
> outside my/our control?  Or is there a way I can ask get_iplayer to
> downrate the SAVING LIVES AT SEA recording (for example) so that it
> still saves at 1920x1020 resolution, but at a lower bitrate?
>
>               Thanks all      ... David
>
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