Date: Fri, 18 Apr 1997 07:44:13 -0400 (EDT) From: Peter Dufault <dufault@hda.com> To: hasty@rah.star-gate.com (Amancio Hasty) Cc: hackers@freebsd.org Subject: Re: video capture driver interface to file system? Message-ID: <199704181144.HAA17161@hda.hda.com> In-Reply-To: <199704181119.EAA04704@rah.star-gate.com> from Amancio Hasty at "Apr 18, 97 04:19:52 am"
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> Lets see, > We can daisy chain buffers in physical memory pending upon the resolution > and the amount of memory available for the system. > > A good resolution for mpeg is 320x240 30 frames/sec for yuv12 that translates > to 3456000 bytes/sec so lets called it 3.5MB/sec substain thruput. What kind of performance can you get now through the file system to your disks? On my not-fancy system I see 1974857/sec saving 30 seconds of "video" at a block size of 3456000 to a Fujitsu disk. (dd if=/dev/zero of=/sd1/A/foo bs=3456000 count=30). Note that I've optimized nothing. Since you can apparently collect the video into a suitably aligned user buffer and I assume that there is some FIFO on the board to give you some time to reprogram at frame done interrupt time, a simple driver with no double buffering other than a regular start queue (so that the done interrupt has a place to store incoming data in), "team", and "dd" may be all you need to store video through the file system on a lightly loaded fast system. It will provide a starting point to see where to focus our efforts, and "dd if=/dev/yuv12 of=~/clip.yuv" is a good interface to support even if only for debugging. Peter -- Peter Dufault (dufault@hda.com) Realtime Machine Control and Simulation HD Associates, Inc. Voice: 508 433 6936
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