I've checked over the last bunch of messages and didn't find anything on this. I'm capturing AVI using the ATI AIW Radeon with a dual 933 MHz P3 system. I'm trying to do uncompressed or DV software encoding, and there are just a few dropped frames. But the audio sync problem is pretty bad. Is this a simple frame drop/computer power thing? I've tried VirtualDub with audio sync feature on, and it doesn't seem to help. Also the MPEG2 encoding using MMC 7.1 seems not to work or eventually generates a blue screen. I'm running Win 2000.

Strongly considering getting a Pinnacle DV500+ so I won't have all these problems.

-- Bill Katz (WTKatz@yahoo.com), May 22, 2001

Answers

Hi Bill, I know EXACTLY where you are coming from on this. I have a 1 GHz Athlon with the AIW Radeon, I run Windows 2000 and a/v sync problems have been a constant problem for me. By the way, I use MMC 7.0. I have some suggestions, but I think the bottom line is that this is something you and I probably just going to have to accept and deal with. I make a lot of SVCDs and I typically use Nero for burning. I record directly to MPEG-2 with a bit rate of 2.594 Mbps. Since the limit for SVCD is 2.6 and although ATI uses a constant bit rate, the bit rate does actually spike higher than 2.6, technically I am making SVCDs that are not compliant. Once you go over 2.6 Mbps on the video bit rate, you're not in compliance. I have played with I-Author a little and I have noticed that it totally freaks out if your video bit rate is not 100% compliant and gives you all kinds of bad a/v sync problems. If you drop the bit rate low enough to totally stay in spec, it's easier to stay in sync. My experience has been that anything I record longer than 30 minutes will have at least minor A/V sync problems, even if the source recording is in perfect sync. So what to do? You might want to get a copy of the bit rate viewer at www.tecoltd.com. You can use the free one to look at your video bit rate and see if your video is totally in spec (it never goes above 2.6 Mbps). If you buy the commercial one (roughly $27 US with the exchange), you can use it to modify your demuxed video stream. I use it to turn sequence headers on - ATI does not always turn these on. I use MPG2VCR (www.womble.com) for editing. Unfortunately, it is $249. However, it's a great tool and it has an audio option under multiplexing to move the sound forward or backwards. You can fix a lot of audio problems with this. I find that if I use a setting of -0.100 (I think this is fractions of a second) that it fixes most of my audio sync problems. Once you've multiplexed with the right audio offset, you can burn. Video less than 30 minutes almost never has a/v sync problems for me. So to summarize: If your video is SVCD compliant (or VCD compliant) it helps. MPG2VCR can be used to offset audio to deal with this kind of problem. You might also be interested in the program ReMPEG. It's available at www.doom9.net and other places. It can drop the bit rate on MPEG-2 video and make sure it never goes above a settable threshold.

-- Jason Shumate (Jason.Shumate@sita.int), May 22, 2001.

Thanks for your quick response. I haven't been able to do I-frame only MPEG2 capture at all yet, so I'm not sure if that works. I'll try MPEG IBP when I get back using one of the presets.

But have you had audio sync problems when capturing AVI, not MPEG2? I figure I should at least be able to capture 352x288 uncompressed but I still wind up with audio sync problems, even when going to a ATA100 IBM 60GXP (reasonable write throughput).

-- Bill Katz (WTKatz@yahoo.com), May 22, 2001.

For uncompressed AVI capture (especially larger frame sizes) you will need VERY fast I/O. I've played with uncompressed AVI at frame sizes up to 720x480. CPU speed is not the issue. Disc I/O is 99 percent of the problem. To give you an example of what the ATI Rage 128 capture card can do with various codecs check this web page:

http://members.home.net/richa/codecs.htm

Although capture was done with the aforementioned ATI AIW Rage card, you can examine the bit rates and subsequent file sizes as well as other information that will give you an idea of the massive I/O needed for full screen uncompressed AVI capture. Actually you are looking at needed sustained rates of around 1.2 GIGabyte per minute.

Any dropped frames of course are going to cause problems, including audio sync. You can reduce the problem somewhat and still capture full screen size if you imploy a compression codec. Examples on that page show various examples. By using a compression codec (like MJPEG for example) you take advantage of the fact that your computer's processor can compress the video as captured at a faster rate than your I/O can write the video to the hard disc. The more powerfull the CPU the more options and higher quality you can use with compression.

As for mpeg real time capture with the ATI, that another looonnnggg story. FWIW, I'm doing SVCD capture with my AIW (rage 128 32mb) and don't have the frame drop problem at all. But I seem to be in the minority as many guys have problems with the mpeg ATI capture. Also at my other web site, (www.pcphotovideo.com) you can see examples of SVCD captures using the ATI card. Good luck ..

-- Rich (rich@pcphotovideo.com), May 22, 2001.

Thanks for the data Rich. I'm using an ATA-100 IBM 60GXP (the new version of the 75GXP), so it has some pretty good write throughput.. at least 20+ Mbs sustained (I thought). The benchmarks using artificial disk measures indicate it has plenty of bandwidth. And sometimes, when I capture 640x480 native (no compression) with CD quality sound it doesn't drop more than 1 out of 100 frames. But the audio sync problems seem much worse than that kind of a 1% drop rate.

I just ordered a DV500+ for $673. Premiere 6 and all the other software make it worthwhile. If that works, I'm going to give the ATI AIW Radeon to my Dad since he watches TV mostly.

-- Bill Katz (WTKatz@yahoo.com), May 22, 2001.

I think you'll be much better off with the DV500 Bill. But you are making a common mistake that many people make regarding dropped frames. 1 percent in my book is totally not acceptable. You are "assuming" that one percent is spread out over the entire file. Maybe, but most likely NOT. Let's take a very small one minute capture. In rough figures at NTSC speed, you are looking at about 3,600 frames. (30 Fps) One percent of those frames is 36 frames. But if you had a "spike" and dropped them at once you are looking at over one full second of frame drop. I find that mostly when right at the limit (and a sustain 20 Mb/s is really not enough) you don't drop the frames (one every couple seconds) More like 15 or more at a clip. 15 frames is more like 1/2 percent of a one minute capture. But will result in something like a full half second audio sync problem. And that's only 1/2 of one percent dropped frames over only one minute. Add to that something like 15 minutes total and you stand the chance of increasing that sync problem quite a bit.

Just for kicks, you might want to check out a program called "AVI_IO". It's one of the best AVI capture programs out there. Although it's very inexpensive (25 bucks US) you can download a functional trial that will allow something like 20 GB? of capture. It's limited to one month of use. But the author puts another new copy up every month. It has features that will work with the ATI AIW cards so you can set up automatic start and use the ATI's tuner. It also will spread the captured video over multiple drives. And it will also "automatically" do something (like padding or something) when ever there are dropped frames which ends up keeping the audio in full sync. I've used the full version to capture 40 GB of AVI across 2 each 20 GB drives. Note .. this was NOT a RAID setup. He also gets around the 2/4 GB limit by allowing you to split automatically the saved video into multiple files that can be up to 4 GB each. And during the change from file to file (or hard drive to hard drive) it does not drop a single frame. You can get a sample from my old web site. http://members.home.net/richa/ If you are going to do any serious AVI work, that and also the Freeware VirtualDub are two "must haves".

-- Rich (rich@pcphotovideo.com), May 23, 2001.