VirtualDub and Audio Sync

[herbapou]

Hi,

First let me say I am a noobs at this. Been looking at the video capture/editing "world" for only 2 days now. I am in the process of testing different ways to record videos to my HD and then put it on a CR-R with the highest possible quality.

My Hardware:

PC: I have 3 pc`s but the one I install my ATI card in is the pentium 4, 1.5 gig with the 40gig HD (My best machine)

Card: ATI Radeon Vivo 64 meg DDR (it has video in)

OS: Windows XP

Drivers: Got the latest driver from ATI site (for win XP).

Capture: Got the latest capture soft from ATI site for XP (version 7.2)

Video input is coming from an RCA cable hook into my Bell ExpressVu model 3100 sattellite dish receiver or my Hi-Fi Video.

Audio input goes into the line-in of my sound card



On the first day I capture lots of different video clips (1 min in lenght) using all kinds of settings with the ATI capture soft (VCD, SVCD, mpeg-1, mpeg-2, from 1000 kbs to 5000 kbs, ....)

MY PROBLEM:

Yesterday, I downloaded VirtualDub. It work right away but when I capture the audio is out of sync with the video.

My goal here is to make DiVx avi`s straight off without having to convert the capture file afterward. The settings I used for video is DivX compression at 500kbs and for audio mpeg layer-3. I set resolution to 640x480. BTW you cant seem to be able to configure the audio source in this software. I had to "unmute" my soundcard line-in to hear audio. To start capture I used the F6 key and fix the stop conditions to secs > 60.

The capture seemed to work fine and produce 4 meg avi file after 1 min of recording. BUT the audio / video are out of sync on playback!!! Help :)

[herbapou]

Found this about this problem so far:

BUG: Audio not synchronized during capture 1.4c (11759) fixed: 1.4d

Symptom: VirtualDub's capture mode produces AVI files whose audio isn't synchronized with the video. Compatibility mode capture (F5) is not being used.

Cause: VirtualDub only corrects capture timing by 1ms per audio buffer. Audio blocks are always at least half a second long, so this limits VirtualDub's timing correction to 0.2%. Some video/sound card combos are off by more than this, and VirtualDub doesn't have enough +/-1ms chances to correct for it. Note that overclocking the PCI bus can seriously exacerbate this problem. (Thanks to Korey Atterberry for help in diagnosing this problem.)

Workaround: Capture PCM (uncompressed) audio and override the default audio buffer size in Capture > Settings; the value is in bytes. For 44KHz/16-bit/stereo, use 17640 for a 100ms block size.

And :

The audio isn't in sync in the capture file.
Obviously, it's a deity's revenge for us daring to put audio and video capture on separate clocks.

If you are running VirtualDub 1.4c or earlier, check the Knowledge Base for a possible workaround if your sound card isn't very accurate. (This problem will be fixed in V1.4d.) Also, if you're using compatibility mode, to capture, don't -- for VirtualDub to resync the audio during capture, you must not be using compatibility mode, and timing correction must also be active (it's in the capture menu).

The "lock video stream to audio stream" option in settings only works for compatibility mode; it sets the frame rate of the video stream so that it's the same length in time as the audio one. This is a nasty way to get audio in sync, because it will make editing harder -- to coerce the clips to a single frame rate for rendering, frames will have to be dropped or duplicated. It also doesn't work well if the timing relationship between audio and video drifts over the course of the capture.


Will test this in a few hours