On Sat, Sep 26, 2009 at 06:28:12AM +0200, Florian Faber wrote: > Fons. > > > Not really. Suppose you have to do this: > > > > 1. copy an audio track from a video recording, > > 2. do some work on it, > > 3. copy the result back to the video recording. > > > > Your (nominal) sample rate is 48k, the video is > > exactly 100s long when played at the exact frame > > rate. > > > > If the the clock used by the video equipment and your > > sample clock are not coherent (not derived from the > > same source), there will be a relative error between > > them, both in steps 1 and 3. > > If the source is analogue video (and analogue audio), you derive your > word clock from the VBI/video lines or SMPTE, if you have this information. > > If the source is digital, well, there is no problem, since you work on a > fixed number of samples. > > So please tell me how this can ever happen in real life?
Deriving the word clock from the timecode or video frequencies, or ensuring both audio and video clocks derive from the same source, is of course the real solution to this problem. But it does assume you have the hardware to do this. Slaving a sample clock to SMPTE could be done relatively easily in software provided you can control the sample clock in software in small steps. It doesn't even require decoding the SMPTE, just extracting the bit clock is enough. This is why I asked you about this feature in the RME drivers some time ago. Ciao, -- FA Io lo dico sempre: l'Italia รจ troppo stretta e lunga. _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/mailman/listinfo/linux-audio-dev
