On Tue, 5 Aug 2003, Gerd Knorr wrote: >> If the cost is 396 kilobytes of wasted memory, I'll rather let the driver >> control double buffering itself than the applications. >avoid copying data. Having multiple buffers usually helps improving >the performance of the applications. For bttv I've raised the default The point is that if the driver does the n-way buffering, why should applications have even more buffers? I see little point in most cases, but you are right, sometimes it helps (like with SMP system with two or more compression threads...as in streamer). However, almost all programs don't utilize several CPUs so it's better to save the 396 KiB at the moment. In the future, I *am* planning to expose directly the multiple internal buffers to userspace applications via mmap. However, this needs common userspace conversion libraries, so it won't happen until xawtv supports Gstreamer (or some other format conversion library) =) >> No, not at all. Works fine at full frame rate (15 fps) right now. >> No dropped frames. With a single mmap buffer. >Is that still true if xawtv does some CPU-bound processing of the >frames? Writing mjpeg-compressed avi file for example? Haven't tried that... but I have used -noscale -noxv options (which makes xawtv slow) on relatively slow CPU (P2 366 MHz) and as long as the CPU usage is less than 100%, I don't see any problems (i.e. no lost frames, which are reported by the driver to the kernel logs).
