[MEncoder-users] pullup question

[Scott W. Larson]

Matyas Sustik wrote:
> This was the best explanation I have read on the problem!  Thanks!

I've spent some time over the years trying to figure it out. It's sad to
come up with filters that turn broadcasted HD content back into 24 fps...
only to see them start failing when the affiliate gets a new encoder or
changes something.

> Yes, we can try to improve the filters, lowering thresholds for duplicates
> etc. but this really should be addressed upstream.

One thing I was playing with for 720p was a "weighted" decimate. The logic
went something like this: if the filter has decided that a frame is not a
duplicate of the previous frame, then it's "X" likely that the next one
will be a duplicate. If it believes the frame IS a duplicate of the
previous frame, then it's "Y" likely that the next will be too. If the
last TWO frames were found to be duplicates then it's "Z" likely that the
next will be a duplicate too.

You would specify "X", "Y" and "Z" and it would multiply these values with
amount of change in the frames by them, making it more likely or less
likely to consider a frame to be duplicate, depending on whether it
determined the last one or two frames were duplicates. With some careful
adjustment and a lot of luck, it would actually lock on the 2/3 pulldown
sequence.

There is a way to specify duplicate frames in MPEG-2 and it was intended
for exactly this kind of situation. No network uses it. ABC can't because
affiliates are decoding and reencoding an MPEG-2 feed from the network so
the flags are lost. Fox could certainly use it with their splicer system
since the affiliates pass Fox's MPEG-2 stream bit by bit, but they don't
use it. I don't know why not.

> So how do we make them care about it?  If there is any effort in place to
> remedy this problem I want to sign any petition etc.  We need something
> along
> the lines of "truth in lending" but for broadcast quality.

Their only goal is to provide good pictures to their audience. If it looks
good to viewers' eyes then there is no problem.

>> many people think the reduced bit rate 720p content looks better because
>> 24 fps content looks smoother when each individual frame is smeared
>> between multiple frames.
>
> Is that what some people call "film look", right?

The smearing goes against the film look to some degree. It does make
movement and pans smoother since there is much less strobing. Of course
strobing probably isn't what people are talking about when they want the
"film look"!