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

[Jarred Nicholls]

On Thu, Dec 17, 2009 at 10:45 AM, 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!
>

If the 720p source has much more movement than the 1080i source, then that
result doesn't surprise me.  That's the way CRF works when you don't set qp
or the bitrate...less "expensive" frames receive less bits than more
expensive frames.  The expense of a set of contiguous frames depends upon
rate of change (movement), with all things being equal.  If the 1080i source
is like an interview of a person, or has a big fat watermark or a constant
background color...etc. etc...then CRF will decide that the frames need less
bits.  Your resulting resolutions aren't "too" far off (960x540 vs 768x432),
so those numbers make sense.  CRF isn't perfect but it does a great job on
average.  You can try setting a target bitrate or a lower crf on the 720p
encode.

Also, this is more suited towards x264 and should be on their list...hehe

Jarred


> 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
>