[FFmpeg-user] which blur filter should I use?

[Lingyuan Wang]

On Mon, Nov 25, 2013 at 4:08 AM, Lou <lou at lrcd.com> wrote:
> On Mon, 25 Nov 2013 01:41:19 -0600
> Lingyuan Wang <lwanghpc at gmail.com> wrote:
>
>> I'd like to downscale my video, 2160p to 1080p for example, which
>> pre-bluring filter should I use?
>
> Why do you want to blur before scaling?
>
>>  I understand ffmepg provides boxblur and smartblur.
>
> There is also sab and unsharp.
>
> http://ffmpeg.org/ffmpeg-filters.html#sab
> http://ffmpeg.org/ffmpeg-filters.html#unsharp

Depends on the original material and how sharp it is, generally
low-pass pre-blurring is a common practice, otherwise the result could
be filled with ugly edges.

sab looks very similar to smartblur, what algorithm does it use? (I
still don't understand why sws_scale() is used in both filters even
the input/output dimensions are the same...).  I use unsharp
afterwards to get some sharpness back.