18..22 frames delay
by max verem
on
Oct 28, 2005 at 1:07:55 pm
Hello!
I use SD-Connect for 1394 DV stream to SDI convertor and found VERY long delay between time of frame written to AVC device and time of same frame appears on SDI output.
As i correctly understand SD-Connect has own long ringbuffer for DV data recived from external devices (PC for example). Is it correct? What is real buffer len? Is possible to decrease ring buffer length up to 2 or 3 frames?
If such delay present, why this does not present in documentation?
I use SD-Connect in Rack/Camera mode 1394->SDI.
BTW
It's second message in forum with such subject.
I found almost identical message: "18frame delay by torinb on Aug 24, 2005 at 2:46:44 pm" and there are NO ANSWERS!
Re: 18..22 frames delay by John Schell on Oct 28, 2005 at 3:57:51 pm
Hi Max,
The SD-Connect does have a buffer internally (it has to). In 1394 deck/camera mode, the buffer is 20 frames. In a editing app mode (FCP, premiere, etc.) the buffer is 6 frames. The buffer is very long in deck/camera mode because the cameras and decks can be off on their 1394 bus frequency due to pulling data off a tape. If the motor on the tape control is off by a fraction of a percent, the buffer in the SD-Connect will underflow or overflow. We have the large buffer to ensure that this does not happen (the video will be lost). When the data comes from a computer, this is not a problem because the hard disk can randomly access the data at any point in time.
Hopefully this answers your question.
Regards,
John Schell
Convergent Design Inc.
PS I believe that in regards to the previous question on the forum, the poster called us and we answered their question.
Re: 18..22 frames delay by max verem on Oct 28, 2005 at 4:07:46 pm
Dear John!
In our case 20 frames is inapproriate at all and cause degradation of realtime responce in our playback system. Is possible to descrease up to 2 frames (or 3)? (that could save our current situation).
In a case hard coded in firmware is possible to patch firmware files to setup new constant for delay in Deck/Camera mode?
Is possible to add 'Deck/Camera 3 mode' with lowest possible value of ringbuffer size?
Re: 18..22 frames delay by max verem on Nov 1, 2005 at 3:24:59 pm
Dear John!
I'd like to return to my problem solving with too long buffer.
I bought TWO SD-Connect instead of Canopus ADVC-300 in hope that software upgradeable device has a future and could be easy adopted to any tasks. But now have a serios problem with HIGH LATENCY of device and that could not be solved in any way!
I also can't understand why professional device should care about low-cost vtr's motor fraction? I had never seen such problem nor with SONY Betacam series vtrs nor Panasonic DVCPro(50) vtrs.
Why these feature (about SO LONG buffer length) DOES NOT NOTICED IN ANY DOCUMENTATION you provided for end users?
Is there are any solution to decrease framebuffer len?
Re: 18..22 frames delay by John Schell on Nov 1, 2005 at 11:48:10 pm
Hi Max,
Sorry for the delay in responding. We will have a new firmware version for you in a few days that will allow adjustable delays with a minimum of 6 frames delay.
Will this minimum work for you?
Re: 18..22 frames delay by max verem on Nov 2, 2005 at 8:04:06 am
Dear John!
I appreciate you for your support! 6 frames is much better then 20!
But its still much, because minimum 2..3 frames is used in driver DMA ring buffer PLUS device 6 frames (device internal) is total 8..9 frames delay. It's still too much for realtime DV VDR!! Is possible to descrease internal framebuffer length up to 2 or 3 frames (depends on memory model used).
Re: 18..22 frames delay by John Schell on Nov 9, 2005 at 7:09:54 pm
Hi Max,
If you download version 1.1.222 (use system - update - get version) it has a variable frame delay for the DV video in DV camera/deck mode. Under playback settings, you will see settings for 4, 6, or 18 frames.
Let me know how this works for you. I'll also take a look at your other post.
