Is this a usual audio sync problem?

[videogen]

Hi, everyone,

I've been reading several posts regarding audio sync problems but I couldn't find one that matches what I'm experiencing.

I'm capturing video from TV tuner in mpeg1 in order to edit it with Virtualdub (cut off commercials and so on). When I open it in Virtualdub I can see that audio becomes out of sync (the closer to the end, the more delay). This happens prior to any compression or cutting in the file, just by openning it. When I play the captured video (mpeg1) in WMP (v.6.4) or in ATI MMC (v7.1) everything goes nicely. Can anyone explain why?

BTW, I´m using a ATI AIW 128 in a Athlon 900 (w/128mb RAM) with Win2K.

[techno]

I can:

ATI SUCK!!!!!!!!!!!!!!!!!!!!!

get a hauppauge wintv go pci, they r cheap and really high quality, DVD!!

anyway:

never capture in MPEG, always use these settings:

No recompression
320*240
YU12
cd quality audio
30/25fps

no a/v synch and high quality.

Techno

[Batman]

Capture directly in Virtualdub, uncompressed avi unless you have a fast cpu you'll need gigs of free space. Visit vcdhelp.com or divx-digest.com for details.

Later on convert to divx

[setarip]

If you're capturing in MPEG1 format, you should use TMPGEnc for editing the file...

[videogen]

Ok, Guys, Thanks for your replies.

But now I'm getting even more confused. I don't think I'll have enough space to do capture in AVI, and since my MPEGs are playing correctly (in ATI MMC as well as in WMP), I can´t see what´s the problem with the ATI card. Frankly, it wouldn´t matter too, 'cause I'm out of money to get another card.

So, do you think there´s a way to do it with my present hardware configuration?

[Batman]

To capture as an avi you don't need another card, just free software called virtualdub at virtualdub.org

If you don't have enough space, you could try reducing the resolution and bitrate. Remember the file size will shrink remarkebly one you convert it to divx.

[techno]

use the settings I gave ya and u will see

Techno

[videogen]

Ok. Thanks again for your answers. I made some testes with short videos and here are the results:
1) Capturing to AVI with Virtualdub creates a file that is almost 280 MB/min. I can't afford that disk space during the capture (I'm capturing directly from TV tuner). Capturing with ATI MMC leads to the same results. I used 29.97fps (see why below)
2) Using ATI MMC, I tried to use the settings Techno gave me, but couldn't find YU12 as video format. Used YV12, instead. With 25fps I got a AVI in which the audio is out of sync (plays after the video). With 29.97fps it seemed as OK as the mpeg file.
3) Using Virtualdub (v.1.4d build 12667) I couldn't find YU12 as video format either. Used UYVY, the only one available. The result is just as good as I got with ATI MMC (in terms of quality and file size)

From my previous tests (still using mpeg), I would say that reduced resolution and bitrate would lead to poor quality after the compression. Do you think the results would be acceptable?

Just to mention, working with mpeg I established that following settings are quite acceptable for me in terms of quality and file sizes: video with 2.5 Mbps, 320x240, 29.97fps and audio with 44.1KHz, 16 bit, stereo ==> lead to a affordable 25 MB/min video file. Even after compression, the results are good; The only problem is the damn sync... Which, BTW, I only noticed when worked with longer videos...

Any other insightful ideas?

[Batman]

Make sure you don't have any back ground apps running.

You may be able to correct the av sync issue in Virtualdub (if it is an avi file), load the file, ensuring both "video" and "audio" are "direct stream copy" and in "video" select "framerate" and "change framerate so that audio and video lenghts match (something to that effect)"

Manually, use synchronizer, back up the file before though.

[techno]

c, u don't understand about quality and quantity!

use the settings I gave u, this is normal for the file size to be big because it is using NO RECOMPRESSION.

u then take this file and convert to MPEG2/VCD/DIVX

then the file size will be low and quality will be there.

I can assure u because I have now captured over 124 music videos.

Techno

[videogen]

Ok, Techno, I´ll give it a try.

Anyway, can you explain why the mpegs play OK in WMP and get out of sync in Virtualdub? What does it have to do with the fact I´m capturing with a ATI card? (sorry if I misunderstood, but your first answer to my post led me to believe that is what you think...)

techno wrote on 05-08-2002 11:08 AM:
hmm...ok

let us see:

right, here is the best method, make sure u have a fast CPU:

use virtualdub:

enter capture mode

use these settings:

352*288/320*240
YU12/YV12
DIVX (3.11alpha) fast motion (15 smooth, 10k/f, 6000 bitrate)
MP3 audio (44100Hz, 128kbps)

use these, this will be no blocks or artifacts, it is great but some quality loss.

Let me know

Techno

[techno]

"Anyway, can you explain why the mpegs play OK in WMP and get out of sync in Virtualdub?"


I really don't know, I think it is because virtualdub does not like playing MPEG files, but only avi files, but I might be wrong.

"What does it have to do with the fact I´m capturing with a ATI card?"

My experience!!!

ATI are not good for capturing, quality is so poor, I can even get you a small 2 second clip if you want to see what the quality was like!!!

Techno

[tenchiwagner]

I feel your pain videogen. I'm running into the same problem, with basically the same setup (except I have 384MB).

Here's what I've learned: Your capture is fine, which is why the saved file from MMC plays fine, but during compression the audio gets out of sync, and it's not just a sync issue that you can offset the audio, it gets stretched. I have a couple new things I'm gonna try out tonight that have a good chance of resolving the issue. I'll let you know.

I understand these guy's comments about using other cards and software, but the issue is what you use it for, and the quality YOU want. The main thing I use it for is taping druing the day while I'm at work. If there's a way to set that up without using ATI's digital recording setup, I'm open to any suggestions.

[setarip]

"Can anyone explain why?"

Because VirtualDub is not intended to be used as a PLAYER - it is video editing software...

[tenchiwagner]

Ok, here's what I've found:

When I was looking at what format to save my recordings, I didn't like the initial results I got with AVI. When there were major movements the image would look distorted with lines in the area of motion. MPEG captures didn't do this, which is why I was going that route. DO NOT BE AFRAID of the results from AVI capturing with this card, when you edit it with VirtualDub, it will come out fine.

Go into your digital recorder settings and make capture settings based on AVI format, and you can even use the DivX codec for the capture. Yes, more processing is involved during capture, but I found it to be a tradeoff since you will be saving a lot less data to the hard drive (I no longer had dropped frames either, before I was getting under 1% dropped, but that still sucks). I was getting a 30 min capture to only take 300MB of drive space (10MB/min).

Then go into VirtualDub and load your capture. Add the "deinterlace" filter, accept the settings, and between that and the recompression (pick your favorite settings) it will axe all those stupid motion problems. I'm ending up with great 480x360 DivX encodes (of my favorite cartoons ) that result in about 100 MB for 23 minutes (which is all that is left when you axe the commercials and opening junk).

Let me know how it works for you!