splice speed

[Floatingshed]

I am doing the simplest of operations and running into trouble.
I have two clips the first is a short (10sec) clip encoded with HUFFyuv.
The second is a longer (25 min) yv12 clip which needs some de-noising.

Simplified script:

a=clip1.avi
b=clip2.mpg
a=a.converttoyv12()
b=b.my de-noiser()
a++b

This gives me about 0.5-1 fps!
If I remove clip1 from the equation and just de-noise clip2 the processing speed goes up to 3fps (the de-noiser is very slow!)

Why is a short clip that receives no processing slowing the whole thing down?
It must be something to do with HUFFyuv as I have tried encoding clip1 with XVID and it then runs at the faster speed of 3fps.

Any thoughts? Thanks.

[Selur]

hdd throughput could be a reason for the slow down,... (especially if input&output files are on the same hdd)
for lossless compression files bitrate normally is rather high and hdd speed could matter,...

[Floatingshed]

Thanks.
If that were the case though would the problem affect the whole thing? Surely just the processing of clip1 would be affected and once that has passed through the speed would increase...

[Selur]

probably, once clip1 is handled it should get faster but I'm not sure how avisynth handles the whole thing internally. ;)