-h, nic: extremely STRANGE dshow/vfw/xvid behaviour during wdm capture...

[avih]

you are NOT going to believe this. check this out: :)

i was playing with capture (installed btwincap wdm driver).
i used amcap (the dshow capture sample app that comes with btwincap, apperantly a sample from the dx8.1 sdk), i set the compression to xvid (installed my latest backed up xvid postprocessing build, which is based on the 22-feb build), was changing the preview pin resolution, and when i went back to the preview screen, i saw the LIVE TV POSTPROCESSED by xvid!!!!

so i opened vdub (my postprocessing build is controlled from the encoding dialog), checked "Show motion vectors" in my postprocessing dialog and voila! it showed the CORRECT motion vectors on a LIVE TV preview!!! :)

all the other postprocessing features worked as well (histogram/picture controls/comparision mode etc)

it was quite heavy since i set the preview res to 704x576, so it wasn't 25fps, more like 10fps, but it was working....

how can that be???? encore must have been used to generate the motion vectors, so it was somehow working (and encoding?), but no file (encoded capture or anything else) was generated during this preview.


any suggestion for explenations so i can rest in peace after i die? :)

avi

[edit]
second thought, maybe the preview shows a preview of the final output of the captured file playback? i.e. compressing and decoding to see actual preview as it will show after capturing?.... that opens a nice set of options :) at last for doing some filtering on live tv :)

[-h]

Heh I love post subjects like this.

i was playing with capture (installed btwincap wdm driver).
i used amcap (the dshow capture sample app that comes with btwincap, apperantly a sample from the dx8.1 sdk), i set the compression to xvid (installed my latest backed up xvid postprocessing build, which is based on the 22-feb build), was changing the preview pin resolution, and when i went back to the preview screen, i saw the LIVE TV POSTPROCESSED by xvid!!!!

Not knowing how such a preview filter would work.. I assume it's piping input from the capture driver to XviD for compression, then feeding the output straight into XviD's decoding filter for the preview. Or something :)

I assume it's the default preview behaviour. What if you select XviD as the compressor with some crappy feeble bitrate? I assume it will compress it horribly, then decode the horrible picture for your enjoyment.

how can that be???? encore must have been used to generate the motion vectors, so it was somehow working (and encoding?), but no file (encoded capture or anything else) was generated during this preview.

I guess amcap is better than I gave it credit for :)

-h

[avih]

-h, yup, you are right.
selecting crappy encoding params gives beautifull crappy preview lol
so, it's very usefull when you want to see how your capture will look, without capturing and playbacking...

interesting to note however, this happens only when selecting preview colorspace as rgb32. anything else didn't produce this 'true' preview.

overall, this amcap if working suprisingly nice, has control of everything audio/video compression/preview, overlay etc.

i'm starting to think in sin ;), and maybe try to start capturing with amcap instead of vdub.... (vdub uses the vfw wdm wrapper, which has some overlay bugs, and a/v sync is not perfect (constant small delta between audio and video, was fine when true vfw driver used)). amcap gave me nice results with nice control........

did m$ produce a descent usable sample here??
lol

[-h]

Hm that rgb32 fact is interesting.. probably hard-coded somewhere in amcap, as there's no reason the yuv colorspaces couldn't do the job even better ;)

I remember trying amcap a while back, but something was horribly disagreeable about it. I think it was the disk writing behaviour - VDub's write controlling managed to max out my disk fairly well, but amcap's habit of writing huge wads of video to disk at once killed my sessions after a matter of seconds. Haven't tried it now that I have a decent computer..

Well actually, I just do all my capturing via firewire and a DV handycam, so I get pretty good sync/quality as things stand ;)

-h

[chemmajik]

Wdm wrapper there's your problem hehe... I never could get any interlaced resolutions to work with that wrapper without dropped frames. So I stick to old faithful vfw1.1e

[avih]

yes, that's whay i said.
however, vfw driver won't install on xp, and i'm satisfied with my current conf of the wdm driver, which has more features than the vfw driver.

eventhough, in vdub, with wdm wrapper, i could capture full res interlaced (720x576) no problem, just without the preview or overlay during capture, which is a known issue with the wrapper.

pls also note that wdm wrapper was not the issue of this thread, but the very nice feature of amcap to do a preview of actual compressed->decompressed video in rt without actually encoding.

[chemmajik]

Hmm I didnt think about it, until just now when you replied. So it makes since for users using a wdm wrapper to get a preview of interlaced resolutions.