> This is not "applicable". > > I've had frame dropping issues myself with a SAA7134 card, so I > investigated the driver and the card itself (on register level). > > First: every PCI TV-card works using PCI bus mastering (DMA). So for the > actual capturing of the frames close to no CPU cycles are involved at > all. You can have a system running at 100% load and still receive all > frames without drops. Of course you will need to do something with the > captured frames, like raw writing to disk or encoding. > > The reason in general for frames being dropped are: > - the capturing card not being able to transfer frames over the PCI > bus, e.g. because of high usage and high latency of other cards; if this > is for a short time, you will notice distortion in the picture, for > longer times it shows as dropped frames. > - the user application not gathering the captured frames quick enough, > causing the PCI busmaster buffers to overrun. Most drivers will cease > capturing though at all, then. > > The SAA7134 has an additional issue, and that is that it drops frames > with no good reason. To be clear: the frames are not dropped by the > driver nor the application. It's just the SAA7134 that decides not to > forward a frame. It looks like it's a synchronisation issue, as the > frame dropping occurs more often when reception is poor. > > BTW you can never trust the synchronisation of TV cards. Therefore > capturing programs should always explicitely keep/fix a/v > synchronisation. Mencoder does something like that, transcode (cvs) v4l2 > import module and nvrec do it too. The video capturing feature of other > programs (like ffmpeg, transcode using v4l, mjpegtools) are actually not > suitable for capturing video directly. > > BTW2 a Pentium II should be sufficient to capture full resolution to > mjpeg. You don't need top-level hardware at all. I'm currently usually using ffv1rec which is based on nvrec and does a great job at keeping things in sync. Take a look at the avidemux.sf.net project for a copy. If I attempt to capture in MJPEG/MPEG4/XVID at full D1 PAL i'm usually ok with zero or 1 frame drop over a capture, If I switch to HUFFYUV then there are problems which probably relate to disk i/o. Also when the HD gets too full i'm in trouble. Steve
