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h2video.nl  
#1 Posted : Friday, February 15, 2013 4:02:52 AM(UTC)
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Hi martin,

I noticed a lot of dropped audio samples testing my setup with the C920 webcam. I did some tests with various combinations. Here are the results:

1. when i record only sound I get no dropped samples at all - reported in the audio-settings info tab.
2. when i connect the C920 I start getting dropped samples reported in the audio-settings, but not in the recording info tab.
3. the dropped samples start with one then 2 then increasing.
4. when I disconnect the cam only and leaving the sound recording the dropping stops.

I connect using the audio-capture tab. The c920 i only connect and disable the sound capture (select none).
The sound capture also shows an empty input window. When i open the info-tab it reports also video-settings (res 32*32, 30 fps etc etc).

I have tried various combinations of quality settings (41 - 48 hz etc), line mic input, USB sound input etc.

My conclusion is there seems to be some sort of conflict within the VMIX sound processing. Since the only variable triggering the dropping of sound samples is when I connect the cam.

I don't have this using black-magic shuttle, but I have to have all sound parameters in-line (48khz 16 bit).

could you have a look at this...

greetings,
stefan
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#2 Posted : Friday, February 15, 2013 5:28:06 AM(UTC)
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Hi Stefan,

What is the audio device you are using?

Regards,

Martin
vMix
h2video.nl  
#3 Posted : Friday, February 15, 2013 7:13:45 AM(UTC)
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Hi martin,

I have tested an external mic (Rode video-mic pro) in two ways:

1. connected to the mini-jack inut, using the computers audio device
2. connected to a simple USB sound card (speedlink VIGO).

Both show the same problem: no dropped frames if i capture only the sound, but samples start dropping when I connect the camera seperately.

For recording I use VMIX audio.

Using the build in mic of the computer (laptop) and the build in mic of the C920 also show dropped samples in combination of using the camera.

Is this enought info?
greetings Stefan
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#4 Posted : Sunday, February 17, 2013 9:34:37 PM(UTC)
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How many dropped samples are you seeing?

A small number is usually nothing to worry about, dropped samples just means vMix is synchronising the audio to prevent a delay.
That said, some improvements are coming to vMix 9 that should prevent dropped samples in a few situations.

Regards,

Martin
vMix
h2video.nl  
#5 Posted : Tuesday, February 19, 2013 1:58:41 AM(UTC)
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hi martin,
short awnser: about 500 - 600 over a 30 minute recording. i will send you some log files.

there are two issues:
1 samples start dropping when a video capturevdevice is connected. i am testing now with the logitech c920 usb device
2 the number of dropped audionsamples icw the resulting sound quality.

i have been doing extensive testing with the c920 because this usb 2.0 camera is an ideal companion in a very small set-up for lecture and meeting capturing. i have no sound issue using a more extensivevsetup using a bm shuttle and hd hdmi recording.

the camera itself i have managed to get very stable, no drpped frames at all. this is partly because of a recent driver update by logitech and by using a 30 fps ntsc format. (last framerate reports a steady 32 32 32 32....). i am also recording on this framerate.

this framerate also reduced somewhat the dropping of audio samples. over a 30 minute period i see about 500 or 600 dropped samples. audio sync is eccellent. even after testing for 3 to 4 hours of recording: no delay. the result is acceptable, but i see this number of dropped audio samples as a risk.

the nr of dropped audio samples and sometimes dropped frames varies with actions i take within and outside of vmix. i have not really tested this extensively but certain actions ( like closing and opening the vmix window) can lead to more dropped audio samples and to the dropping of frames.

as mentioned before: there are no dropped audio samples recording sound alone, the dropping starts when adding this specific capture device. i will send you some log files.

greeting,
stefan
h2video.nl  
#6 Posted : Tuesday, February 19, 2013 5:40:02 AM(UTC)
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just sent you 3 log files by mail. Hope this will help.

See an example of a recording with the C920 here:


greetings
Stefan
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