example streaming program to disk

[BrianBacker]

Does anyone have a vi that can be used to test the throughput of video to disk. I've installed a dedicated SATA drive for streaming 640x480x30Hz frame rate video and cant get all of the frames in real time. My calculations say that I shouldnt be bandwidth limited

Thanks
Brian

[s_a_s]

Hello Brian,

I'm not aware of any VIs out there that test the throughput of data streamed to disk, but there might be one.  Hopefully the owner of such a VI will post here.  Even with a SATA drive, there will most likely be missed frames when doing disk I/O if you are only acquiring images via a grab and writing each file to a separate jpg or png file.  For fastest stream times I would recommend using an AVI file and separating out the frames from the AVI post acquisition.  If this won't work for you then you will need to use a ring acquisition with enough buffers to prevent overflow.

[BrianBacker]

The problem is that the data that i need to write is 16-bit grayscale and according to the NI documentation, the AVI files are only 8-bit grayscale or 24 bit color.

Does AVI have a no-compression setting? I need raw data

I'd be ok with saving the images as one large file and then break them into individual images later.

[David S.]

Hi Brian -

AVI files written with the Vision module are uncompressed by default.  The file definition for AVI is limited to 8-bits per plane, though (which translates to 8-bit grayscale and 24-bit color).  If you need higher bit depths, I recommend acquiring in a Ring with a large buffer list and writing the images to a file in a separate thread.  This allows some jitter in the write process, which can be caught up a few frames down the line.

[BrianBacker]

OK - I have a workaround where i break the 16-bit word into two 8-bit channels and write these to the RED and BLUE channels of a 24-bit AVI file. Then after i make the AVI, I can post process the AVI into individual 16-bit TIFFs afterwords.

Thanks for the help.