Hi Martin and vMix people.

I need to use simultaneously the "vMix Virtual Capture Device" and the "Decklink Renderer". Also, I render the audio using a "Virtual Audio Cable" line because I need the "Default Direct Sound" device for a monitoring application.
The External Output device is a Blackmagic Decklink SDI card.
I feed a Flash Live Media Encoder with the vMix Virtual Capture Device and the Virtual Audio Cable.
I feed the SDI output with the "Decklink Rendered" video and the Virtual Audio Cable; and show this SDI signal in an external device.

I need some help in order to understand and avoid if possible some delays in the audio respect to the video in the SDI output.

If I see in a client the stream from the Flash Encoder, it is difficult to appreciate or measure the difference between video and audio. May be is about one frame (rate is 25 fps, so 1 frame = 40 ms).

But if I see the SDI contens, the audio is clearly delayed between 100 and 200 ms from the video.

I expected the video delayed from the audio in any case, because the about two frames delay in vMix, but I found the audio delayed.

Any idea about the reason and a fix of those delays will be welcome.

Below I describe the platform (I have tested in different combinations):

HW platforms: Intel motherboards with
- Core i3 530 / 2.93 GHz
- Core i7 2600 / 3.4 GHz
SW platforms: Microsoft Windows 7 professional
- 32 bits
- 64 bits
A/V inputs:
- Osprey 210 analog A/V PAL. Video: 720x576, 50i, Audio 44100-16-2 audio. Video deinterlaced in the Osprey.
- Video file wmv. Video 720x576, 25p, Windows Media Video 9, 660 kbps; Media Audio 9.2, 63 kbps, 48-16-2
SDI output:
- Blackmagicdesign Decklink SDI card
vMix version:
- vMix Basic 2012 7.2.0.42
- vMix Basic HD 2012 7.2.0.42
vMix settings:
Display: System: PAL 50i or 25p
Output size 720x576
Performance: Prev. Skip 10, Ap. Priority Normal, Out. Format UYVY, Video Render EVR
Ext. Output: vMix Virtual Capture Device and Decklink Renderer
System: PAL 50i or 25p
Output size 720x576
Device: SDI, Port Decklink Renderer
Audio DeviceDirect Sound Blackmagic
Input audio device: Line 1, Virtual Audio Cable
Audio Format: 44100 Hz 16 bit 2 Channels
Audio Renderer: Direct Sound Line 1(Virtual Audio Cable)
Automatic mix audio
Show Master Audio Meter in Main Window

Thanks in advance and best regards from Spain
Antonio

Hi Martin.

Thank you for your advice.

I've been runing some tests these days with the results described below.

I have allways been rendering the audio with the "Default DirectSound Device", and arranged 3 different ways to output the vMix mixed audio through the Blackmagic Decklink SDI:

1.- vMix Settings -> External Output -> Audio Device: "Blackmagic SDI"; Input Audio Device: "vMix Virtual Audio Capture"
The audio received through the SDI has a starting delay from the video about 50 ms, and increases about 160ms/hour.

2.- vMix Settings -> External Output -> Audio Device: "Blackmagic SDI"; Input Audio Device: "Stereo Mix"
The audio received through the SDI has a negligible starting delay from the video, and increases about 80ms/hour.

3.- vMix Settings -> External Output -> Audio Device: None; Input Audio Device: None
Windows->Sound->Recording->Steereo Mix-> "Listen to this device": checked and directed to Blackmagic Decklink SDI audio output
The audio received through the SDI has a starting delay from the video about 50 ms, and no increase is apreciated.

The third arrangement has the clear advantage of no drift in the video<->audio delay found in the SDI output.
I hope your comments. Thanks again in advance.

Best regards,
Antonio