Date: Wed, 7 Mar 2001 00:04:11 -0600 From: Pete McKenna <pmckenna@qwest.net> To: Tommy Johnson <protius@bobdbob.com> Cc: freebsd-multimedia@freebsd.org Subject: Re: Video capture Message-ID: <20010307000411.A41216@otto.oss.qwest.net> In-Reply-To: <200012120541.eBC5flN19347@teryx.bobdbob.com>; from protius@bobdbob.com on Tue, Dec 12, 2000 at 12:41:47AM -0500 References: <3A312120.DB69E030@mitre.org> <200012120541.eBC5flN19347@teryx.bobdbob.com>
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Tommy, thanks for posting this, I think I have it close to working, but am wonder how you told the BT8x8 card what input to use. I can capture and it seems happy but I end up with a blue screen. What input options are set by default ? and where are they. I'm trying to capture from the s-video in mostly. Thanks Pete On Tue, Dec 12, 2000 at 12:41:47AM -0500, Tommy Johnson wrote: > >Tommy Johnson wrote: > >> > >> >Is it possible to capture video on FreeBSD into MPEG with just a BT8x8 > >> >based capture card? Has anybody successfully captured video and or > >> >coverted the video to DivX ;-) (MPEG4v2)? > >> > >> I've done video capture to mpeg 1 with a BT8x8 card, at 352x240 resolution. > >> The entire scheme is capture to an uncompressed file, then compress video > >> and audio seperately, then merge the two streams in to one system stream. > >> > >> If there is interest I can make a tarball of my alleged software and > >> put it on the web. Its extremely non-pretty, but it works. > > The tarball can be found at http://www.bobdbob.com/~protius/software/video.tgz > > This is /extremely/ alpha quality, its more the proof-of-concept code than > anything. I use it every week to digitize a public access TV show a friend > of mine does though. The way the last month has been, attempting to get > around to cleaning it up would result in just too long of a delay. > > >That would be great, I'm sure I'm not the only one who wants to do this. > >BTW, how much space does an uncompressed video take? My back of the > >envelope > >calculations for a 30fps 30 minute long uncompressed video place it > >around > >76,032,000 bytes, ouch. > > Yea, 'tis a nasty volume of data. I usualy do 352x240x30fps at 16 bpp > YUV, which is approxomately what NTSC does (YUV-422). That works out to > about 9GB/30 minutes. Full resolution would be 36.4GB/30 minutes. > > Harware compression is your friend. :-) > > The problem I ended up spending more effort on was syncing the audio and > video. My solution isn't perfect, but it at least dosn't drift badly over > a 30 minute run. I have two circular buffers in shared memory, the audio > buffer is fed by an independant reader process. The video buffer is > fed by a signal handler, and the main body of the video process writes > both buffers to disk, using a single file. The original implementation > had two files, but seeks between the two writers killed performance. > Every 333 frames, the writer throws away audio samples, to force the two > buffers to line up. Its also dosn't write the same number of audio samples > per frame, since 44100 audio samples per sec dosn't divide by 29.97 frames > per sec. The least common multiple is 333 frames... On my setup, it > almost always has an error of 98 audio samples per cycle. > > Anyway, let me know if its of any use, or how bad my code is... :-) > > -Tommy Johnson > protius@bobdbob.com > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-multimedia" in the body of the message -- Peter McKenna Qwest Internet Solutions pmckenna@qwest.net Main 612-664-4000 FAX 612-664-4770 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-multimedia" in the body of the message
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