Dropping frames

[MadScientist]

hello i have a very unique question - in divx4 (all thoes years ago) you had the option to drop frames about a threshold. my question is (using divx3 & nandub with Gknot stats editor) can u chose exactly what frames you want to drop using nandub and an ECF file and the command.

@100-110: M=000,R=0270,D
or
@100-110: M=299,R=0270,CL31,D

if not can some one explain what would happen(i bet ur laufing at thoes commands)
or would Gknot setting the frame size to 0 in the manual correction box

well i would like to kill the ghost frames and frames with still images with high levels of noise (so i am not insane)
thanks every one who helps

well what i mean is: i would like to dupe some frames to replace others, I am getting a load of unwanted motion vectors taking up space in a movie i'm doing and the scene is supposed to be still. But the img must be shifting around on a few pixles up and down and its taking lots of BR in the process

-MadSci

[MadScientist]

well it appears that d.graft is develpoing an avisyth v2.5 filter that will do the job. It can be found here (http://shelob.mordor.net/dgraft/dup/dupnew.html)

[esby]

Dup is probably what you want to do, i think ^^.

More reason to got to dup instead of frame dropping :
(even if this could be done cleanly)
Dropping frames & dupplicating frames are not exactly the same thing.
Of course if you force the framedrop,
this will be as if the frame was duplicated,
but it will be more cleaner to use dup,
and to let nandub create a dummy delta frame instead.
because dropped frames are considered as a problem,
and not as a final suitable state.

On another note, i have constated that some keyframes have parasite noise
which get immediately corrected by the next delta frame following them.
Meaning than hypotically dropping the DF,will probably reduces framesize
but will surely introduces non wanted noise in the encode.

esby

PS:
If anyone has an idea about 'how to produce' KF without such noise,
that would be intersting by the way.

[MadScientist]

i understand that frame 'n' (a dup frame) is the same as frame 'n-1'. so no changes will occur and yes its a dummie frame but needs to be encoded onto the MPEG bit stream, how does a droped frame differ, is there a flag in the "data chunk"?

and to any experts what dould take less bits a dup/dropped?
thanks ur very helpfull every one

-MadSci

P.S Oh and what do u mean "parasite noise" (my english is not that good), but would like to see if u could help - (been playing with key frames for the past few days);)

[esby]

A dropped frame is a frame which size = 0.
That just means the encoder couldn't encode it for some various reasons and has skipped it.
Dropped frames mostly happends when 'leet encoders' try to do xvid 120 fps raws,
the results are easy:
70-80% of frames are dropped because the codec couldn't keep with the data...

esby

[MadScientist]

if a droped frame = 0b and a dupe frame will be encoded with min BR usualy 270k then i will get 152bytes per frame since i have 40,000 frames where relative motion = 0, i have 6MB of wasted space, there must be a better solution. please does any one have an idea on how i could drop these frames.
and how can if be 0b - a record that is has been droped must be kept somewhere?
yeah i heard from friends that dropped frames usualy occur on motion capture when the PC cant keep up with the input frame rate and 120fps lol yeah thats insane :eek:

[esby]

A dupe frame will probably contain minimal data,
which make it small, maybe atomic, but not 0 sized.

A dropped frame has a zero size, the avi index keep track of it.
(the avi index is not part of any frame, of course, hopefully :D )

PS:
Setting up min bitrate to 270 won't mean
you'll end with a frame corresponding to this bitrate.
It's just the inputed bitrate, not the resulting one.
Or in another example, settings bitrate 6000kbit won't give
you a corresponding framesize :)

esby

[MadScientist]

i had a look the actual frame size of a dupe is 152bytes. thats alot :(. (i was doing the calculations with 1200macroblocks(640x480))

does any one know how to drop a specific frame?

[esby]

152 bytes is not really a lot,
and if you consider that 'dropped frame' can froze the player,
depending what you use to decode,
i'll avoid that, for compatibility purpose.

And if you consider a clip of 160mb containing 35000 frames
(approx 20-25 min @24fps @850kbits)
The average size frame is 160*1024*1024/35000 ~= 4793 bytes.
if you compare 152 to 4793, you save 30 times the space,
something quite & still interesting.

esby