[MEncoder-users] compression: 1080i versus 720p

[Grozdan]

With CRF, it's difficult to predict what bitrate it will use for a
specific source. It is perfectly possible for a lower resolution
source to exceed the bitrate requirement for a higher resolution
source if the former has lots of noise in it, contains (lots of) high
motion and (lots of) detail with bright colors. As you said yourself,
the 720p version was more dynamic. Also, if the 1080 and the 720
source are not one and the same video (just differ in resolution and
nothing else) then it becomes even more difficult to compare their
requirements.

Bitrate is very dependent on the source. To give you a small example,
I usually encode DVDs (just cropped, no scaling) and I always use CRF
20 for my encodes. Most of them have bitrates between 700-1200 kbps
but every now and then, there are a few which almost require twice as
much, even though they have almost identical resolution to the others
(usually 720x352). Latest example I can give you is the DVD of
Transformers 2. It has a very clean source (which helps compression)
but the movie is filled with very bright colors, lots of high motion
small details and lots of overall complexity and high motion. At CRF
20, the bitrate stayed for 95% of the whole encode between 2000-2200
kbps

On 12/17/09, Matyas <mplayer.list at sustik.com> wrote:
> Hi All,
>
> I apologize in advance if this list is not best suited
> for this question.
>
> I have encoded several 1080i and 720p OTA sources.  The only
> difference was that I used deinterlacing for the 1080i and that
> I scaled differently: I scaled the 1080i to 960:540, while the
> 720p to 768:432.  I used crf=23 for both encodes with h.264.
>
> The resulting bitrate for the 1080i sources varied between 1100
> and 1900.  For the 720p sources it was over 2000.  The 720p source
> is more dynamic but I still was surprised to see the much higher
> bitrate on a smaller resolution.
>
> Could you comment on this observation?  Thanks!
> Matyas
> -
> Every hardware eventually breaks.  Every software eventually works.
> _______________________________________________
> MEncoder-users mailing list
> MEncoder-users at mplayerhq.hu
> https://lists.mplayerhq.hu/mailman/listinfo/mencoder-users
>