Latency When Recording

[eldermfo]

I have been successful in creating video files using Vidblaster Pro with three camera sources. But when I play back the files there is considerable latency between the audio and video. I have used video editing software to try to sync the video and audio but found that while it is synched in one place a few minutes later it is off again. I am using an audio mixer connected by a usb to xlr adapter (my laptop does not have a line-in, it just has a mic input). How can I solve this problem?

[Mike]

If latency varies independently of the camera, than the only reason I can think of is that it's introduced in the PC and the CPU is having a hard time keeping up.

[Alain Bouvette]

I just unboxed a Dell XPS system yesterday. It still has the Dell bloatware installed:
- Intel® Core™2 Q8200 (4MB,2.33GHz, 1333FSB)
- 4GB RAM
- ATI Radeon HD 4850 512MB
- 640GB Serial ATA Hard Drive (7200RPM)
- XP SP3
Using a USB microphone mixer with XLR inputs for audio, one Sony HDD camcorder connected using EasyCap and another camcorder using FireWire, I recorded an uncompressed file in VidBlaster Pro v0.39 @ 320x240 as well as saved a Flash stream using FME 2.5 and found audio synch issues with the uncompressed AVI file saved by VidBlaster.

The uncompressed AVI file is @75mins long and 31GB in size. The flash file was only a fraction of that since it was encoded at @250kbps but on playback, there are no audio synch issues with the FLV file.

When I get a chance, I'll see if the audio synch issues (in Windows Media Player) disappear if I play it on a different PC or re-render the AVI file to WMV, FLV or something else.

[Mike]

As a reference, please use compressed WMV (10 Mbps). It has auato sync correction built in and with your setup you should not have a noticable sync error, and it should not change over the entire recording. The uncompressed version does not have this, and could introduce sync problems if you have lost frames during that period (possible due to short system interrupts). If you can confirm this, I can see if I can solve this. So far noone needed the uncompressed option (as the 10 Mbps is already hq). In fact I have been considering dropping it altogether.

[Alain Bouvette]

Originally Posted by eldermfo

I have been successful in creating video files using Vidblaster Pro with three camera sources. But when I play back the files there is considerable latency between the audio and video. I have used video editing software to try to sync the video and audio but found that while it is synched in one place a few minutes later it is off again. I am using an audio mixer connected by a usb to xlr adapter (my laptop does not have a line-in, it just has a mic input). How can I solve this problem?

Hi, have you been able to resolve this? I have to run a few tests myself as I'm experiencing the same. Basic setup:

Using only VidBlaster Recorder (save as 10Mbps WMV file):
VidBlaster Pro v.046
- Recorder @ 640x480
- 30fps
- mobilepre usb (mixer) with XLR microphone
- camcorder using EasyCap

I wonder if the encoding to WMV (using VidBlaster's Recorder module) is the problem? My FLV files don't seem to have that problem (I use VidBlaster's Stream module and send to FME 2.5 and save a local FLV file). Again, I'm grasping at straws here. I will try to test (& document) a few scenarios.

[Alain Bouvette]

Has anyone noticed a difference in latency/lag between audio and video when VidBlaster saves the Recorder output to different formats? For example, I seem to get less audio/video synch issues if I save my output as MP4 instead of WMV. The video quality isn't as good on mp4 though.
Also, when I play back a wmv file I've recorded with VidBlaster, I notice that its properties say that Windows Media v 8 codec is the encoder. Does this come with VidBlaster or is this something that is dependent on what is installed on the PC?

I recently installed an Osprey-450e card and am testing with 1 or 2 cameras. My microphones are connected to a USB mixer. My PC specs are available in a previous post.

[Scott]

I am using (2) Osprey 100 cards and 1 USB capture device for a one streaming situation with very good results, especially considering the test computer is a P4 3Ghz with 512MB of RAM and a 64MB graphics card. It will be replaced soon, but its interesting to note that the CPU is constantly at 100% but its been web casting non-stop in the auto switcher mode for over a month 24/7, except for one brief power outage for a few hours.

I am very interested in seeing the results from the Osprey 450e card. As far as audio/video synch issues, have you considered using a quality analog mixer and go directly into your sound card? That might eliminate any synch issues with USB. In the above example we are taking the audio feed off of a Peavey mixer into the computer's line input with no synch problems at all and it sounds great.

[Alain Bouvette]

I've done a few more tests. Using the same hardware for all 5 tests:

- Using only FME 2.5, save local file, 320x240 @30fps = no audio/video synch problems
- Using only FME 2.5, savel local file, 640x480 @30fps = no audio/video synch problems
- Using only VidBlaster Recorder to save WMV file @320x240 @30fps = synch issue
- Using only VidBlaster Recorder to save MOV file @320x240 @30fps = synch issue
- Using only VidBlaster Recorder to save FLVfile @320x240 @30fps = synch issue

Can someone explain why this is happening?

[Alain Bouvette]

FYI,
I overcame the synch issue I was having between my cameras and USB mixer by connecting the stereo out on the mixer into the line in of the sound card. I chose the soundcard as the audio device instead of the mixer.
This is the USB mixer, if anyone is curious: http://www.m-audio.com/products/en_us/MobilePreUSB.html
I've also got my hands on an older analog mixer which I hope to play with soon: http://www.behringer.com/EN/Products/MX1604A.aspx

Perhaps someone can suggest the best way I can connect it to the computer to avoid possible synch issues?

Thanks

[Scott]

I have been using a Behringer mixer with great success for a variety of productions including VidBlaster, voice over work and music production. I own a Boss and Tascam mixer as well, but the Behringer is the best in my opinion (quiet, built like a tank, battery powered, etc.).

When using VidBlaster I only use analog mixers and take the input into the sound card to avoid any USB issues and give priority to the video stream. Works and sounds great with no latency issues.