why do the cuts scratch?

[pdottz]

don't mind the topic title but it does make sense for my question...

I use vdubsync to cap and vdub mod to cut the resulting avi.

what happens is this, the beginning of every encode has loud scratching noise 1/2 second before the audio starts. i know the audio during capture NEVER does this cause it only happens at the beginning of every encode.

here's my process since i cap toons. i use avisynth to feed the mjpeg to vdubmod avisynth has all the filters ready.

I select the section of toons i want to cap using the markers in vdub mod. disable audio for the first pass. then setup the the 1st xvid pass.
for the 2nd pass i enable the audio and use lame to convert to 128cbr. and then setup the 2ndpass for xvid.

nothing wrong with video after capping. but audio is always scratched at the beginning no matter if i used directstream copy or converted use the vdub lame filter...

it's been a real hassle having to feed the audio post processing into soundforge to mute the scratch in the beginning and the recompress and mux afterwards.

does anyone know why vdubmod cuts and encodes audio this way? is there a solution?

btw. i use 1.5.10 vdubmod.

[Mug Funky]

hmm.

what audio codec do you cap to? i assume it's just plain old PCM.

what happens if you do your cuts in avisynth (via "trim(a,b)+trim(c,d)+...")?

do the glitches happen after xvid encoding or before?

[pdottz]

Mug Funky.
I capture to plain PCM audio.
I haven't tried capturing to mp3, i don't even know if thats possible.
but the scratches happen whether or not i use avisynth to feed the avi file into vdubmod. also, the reason i use vdubmod at all to cut is this.
sometimes i'll cap like 3 hrs worth of toons straight. since most of the toons have 10 minute eps in each 1/2 hr i do this.
I select the beginning of each "ep'mark it, than the end and mark it. what's in between is what gets encoded. i know you know what i mean, i'm just explaining my process.

i do have one theory though. i'm thinking the audio shifts a bit when the cut happens. not enough to notice when you watch the encode, but enough that it causes the scratch.

oh yeah, this happened when i use to encode to divx also.

also, it's rare when there isn't a scratch, but it has happened where an encode wont have that scratch in the beginning. like 1 out of every 100 encodes will be clean.

[hartford]

@pdottz

When you do your cuts, are the cuts in a silent spot?

I use this Avisynth script to find a silent spot:

Loadplugin("audgraph.dll")
avisource("MyCapture.avi").ConvertToYUY2()
audiograph(last,2)

With this I can see the audio in VirtualDub.

I suspect that your "1 in 100" non-scratch cuts occurs when the
audio is near the "crossover" spot. If you load this script you'll
see what I mean.

[pdottz]

hartford.

you where right.

the way i was choosing my cut points was from the exact from where the commmercial turned black a few frames before the ep started. turns out that even though the frames where black, there was still a few frames of "noise".

this plugin helped. thanks.