hello Gabor, Looks like we're doing more or less the same thing--I'm trying to multiplex up to 8 non-synched PAL sources, but with an external, serial-controlled switch. From what I understand about video, it's impossible in this configuration to guarantee results better than 12.5 fps. (I mean TOTAL frames.. so with 4 cameras this would be 12.5/4 fps for each camera.) At any rate, I've gotten pretty good results (9, 10 fps TOTAL) putting the switching code inside the kernel. Specifically, I change the camera between frames and mark the data according to the currently selected camera. (It's a hack.. I just make the first byte of the image an indicator.) One mistake I made was setting gbuffers=2, thinking that somehow this would get me better "response time". This appears to be an error in thinking, because I actually get much worse results this way. (Like about 5 fps.) It seems to work better with a bigger gbuffers value. This means, of course, that your user-space program will be a little out of synch with what's being recorded though. (For this very reason I have to tag the images.) dI77IHd --- Gabor Kerenyi <wom@xxxxxxxxxxx> wrote: > hi! > > I have a serious problem with the BT8x8 chip. I have > to > grab four channels at the highest framerate. I don't > need > the full frametrate (25 fps), but I need as high as > possible, > the higher the better. > I looked for this problem in the archive and there > was a > thread about it but no solution. > > I use 4 not synced video inputs (PAL). > > There are two problems: > 1. If I change the channel after each field then the > BT chip > sometimes swaps the top and bottom field. I don't > know why. > The BT documentation says it determines the > top/bottom field > from the first HSYNC after the VSYNC rising edge (in > phase > with the VSYNC or not). > I can get the video signal stable if I use a second > read and > drop the first picture. But the framerate is too low > this time. > > 2. The framerate independently from the stableness > is low. > 8 fps/channel for two channels. Well there is a > Piccolo (Eurosys, > using BT chip) card and a windows driver and it can > do > about 16 fps for two signals and 4-5 for 4 signals > (and > of course it never swaps fields). > > So how that card and driver can do it? OK, there is > an external muxer for the inputs, so only one input > is > used of the BT chip. I think this is not a big > difference since > the muxer in the BT chip is also an "external" > device. > > Does anyone have ideas about it? Why does it swaps > fields at all??? > > thoughts from me: > it swaps because the BT chip has an internal sync to > correct bad V&HSYNCs, such as VHS video. Because the > mux is independent from the chip and when another > source is selected it simply follows its internal > timer and > doesn't care of extra SYNC pulses. > > Would it help if we reseted the chip after the > channel switch? > Or simply force the chip resync (if it's possible) > I can get fields swapped if I grab full size picture > (768x576) > in interlaced mode as well. > > Thx, > > gabor > > > > -- > video4linux-list mailing list > Unsubscribe > mailto:video4linux-list-request@xxxxxxxxxx?subject=unsubscribe > https://listman.redhat.com/mailman/listinfo/video4linux-list __________________________________________________ Do you Yahoo!? Yahoo! Shopping - Send Flowers for Valentine's Day http://shopping.yahoo.com
