Video/audio sync problem with mpeg2 original material

mdsh wrote on 5/6/2002, 7:23 AM

I have some mpeg2 material, its a recording from a DVB-T tuner so its ~3.5Mbps mpeg2. It plays perfectly in Microsoft Media Player and Real One.

In VV3a it is out of sync, the audio is about 8 frames behind the video. This is constant and does not depend on which renderer I use.

One interesting thing I noticed, on the timeline the audio ends 3 frames after the video. I was wondering if it is possible that the audio actually starts 8 frames before the video and Vegas is incorrectly making the video and audio start at the same time. This would push the audio out of sync. I do not know enough about mpeg2 files to be able to check this for my self.

Any thoughts from SF on this one? Its a real pain having to slip the audio in order to get it back into sync, but at least it is possible.

--
Mark

Comments

HeeHee wrote on 5/7/2002, 4:55 PM

VV does not handle editing MPEGs very well because they are a lossy compression file. This Sync problem may be a result of the lossy format. You should really use a lossless compression like DV avi or uncompressed avi.

mdsh wrote on 5/7/2002, 6:00 PM

Hi HeeHee,

Thanks for your input. I was trying to convert from the MPEG2 original into DV AVI when the problem occurred.

You may not have understood but digital television here in the UK (and many other countries) is transmitted in MPEG2 format at around 4Mbps. This is called DVB (Digital Video Broadcasting). It is possible to get hold of the raw MPEG data as transmitted using some Hauppauge hardware. You capture the transmission exactly as it left the broadcasters (save for any interference that might corrupt the data while its in the ether). This is the best quality one can ever expect to get for the current transmissions - its often digital from the camera to your computer with only one MPEG2 encode using extremely expensive encoder hardware at the broadcaster.

Oh, and not wanting to argue but DV is a lossey.

Cheers :-)

SonyEPM wrote on 5/13/2002, 10:21 AM

Is there any possibility of recording the feed with a DV camera? Off-air MPEG-2 to Haupaugge/Huffy to Vegas is not a very reliable scenario.

jrstueve wrote on 5/13/2002, 11:33 AM

I've found that my sync problems appear where I drop frames.. the audio is captured, but the video is missing.. so over time with more dropped frames, the audio starts to lag the video...

but that is with a analog video capture... not a directly streamed MPEG2...

mdsh wrote on 5/14/2002, 4:53 PM

There is no possibility of feeding Video from the Hauppauge WinTV Nova-t (USB) into a DV capture device because there is no video output from the device what-so-ever.

http://www.hauppauge.co.uk/html/digitaltv_prod.htm#novatusb

I don't know, SonicEPM, if you are in the USA or Europe. Here in the UK we have Digital Terrestrial TV, MPEG2 transmission with roof top areals. This Hauppauge device can record the raw MPEG2 stream exactly as it pulled it from the digital multiplex.

As far as I can now tell, my sync problem is caused by the Main Concept MPEG decoder ignoring frames which contain corrupt data [1]. Other MPEG decoders, including the standard ones in which are used in M$ Media Player, Real Networks' One and FlaskMPEG [2] repeat the previous frame if they discover a corrupt frame and therefore the sound down not drift out of sync.

So, to recap. As far as I am concerned, editing from these MPEG2 files in Vegas is completely useless.

[1] Obviously, the transmission of an MPEG2 stream via TV areals is bound to produce some errors. I guess the Hauppauge box does its best to recover the correct data but corruption is inevitable.

[2] I would use FlaskMPEG to convert the MPEG2 files into DV AVI's if the AVI's had the same video levels as the MPEG2. Unfortunately, using the SonyDV codec (which came with my laptop) as the output format the video levels are altered from the 16-235 standard upto 0-255 which is pigging annoying. I don't know whether its the SonyDV codec that's at fault or FlaskMPEG in general.

--
Mark

jgourd wrote on 5/14/2002, 6:29 PM

You can use XMPEG to make a DV avi. I use MPEG-2 files ripped out of my ReplayTV 4080 and they sometimes suffer from what you are describing. The MPEGs are sometimes corrupt and I have to re-render then in DV or uncompressed AVIs.

My biggest problem with VV3 and MPEGs is that really large MPEG files take a very very long time to scroll from one end of the file to the other. This is especially true if they were captured using a C-Cube MPEG DSP chip like the one in the Dazzle DVC II or the ReplayTV 4000 series. It is not just VV3 that has this problem either, DVD workshop can take 30 seconds to revert control back to the user when you let go of the navigation scroll bar. My solution is to use Womble MPEG VCR to split it up into small (< 1 gig) chunks before importing them into VV3.

pelvis wrote on 5/14/2002, 8:32 PM

I'm sure this will come as a dissapointment given that you have made a hardware investment, but: MPEG is not an ideal source format for editing. Vegas can open many types of MPEG, but no matter what, you will always wind up recompressing (ergo degrading quality) whenever you render MPEG source material to MPEG.

If there is any possibility of using uncompressed or DV .avi as a source format, you will notice a big difference in application performance and image quality in the final render.

jgourd wrote on 5/15/2002, 1:27 PM

I am curious, which Happauge card? WinTV-D, WinTV-HD, or something else?

mdsh wrote on 5/15/2002, 6:17 PM

Its a Hauppauge WinTV Nova-t (USB). Its not a card, its a seperate USB device. And its not mine but I have been given files captured with it to edit from. I know its not the best format but it is considerably cheeper than poppin into the BBC to get dubs or the original material...

--
Mark

jgourd wrote on 5/16/2002, 5:56 PM

That is not sold in the US. They do have a WinTV-D which does the same thing in a PCI card.