Re: more on frame timing, framerate-changing filters

Hi,

> Hi,
> 
> > > Also, on another matter. I know G1's whole a/v sync system has been
> > > based on a lot of approximations and feedback measurement. This is
> > > great for mplayer, and probably also for encoding from variable-fps
> > > input to fixed-fps avi output with mencoder. However, especially with
> > > the new perfect-a/v-sync mpeg code in G2, I'd really like to see
> > > support for "exact" timing in G2. Maybe a way to use a time division
> > > base and specify all pts stuff in terms of those (exact) units. It
> > > would be much perferred for precision encoding and video processing
> > > work, and nice for output to containers like nut (mpcf) which will
> > > support such things. 
> > 
> > I'de like to see this as well. The sync should not be based on audio
> > but instead on the realtime clock or an external timebase (worldclock
> 
> of course, it's planned as option for g2 sync core
> (sync to any audio or video stream or rtc or any external clock)

Sounds good.

> > cards can be purchased for PC). If the soundcard isn't synked to the
> 
> imho it's far better to sync to sound card, than resampling audio to
> get in sync with wall clock... except for some special uses when wall
> clock sync is more important than audio quality (like streaming media).
> 
> > RTC then one could fix it using sample stuffing or dropping (inaudible).
> 
> how do you do sample drop/insert without hearing it?
> afaik the ntv (?) video capture app does audio resampling (not
> sample insert/drop) to keep the sync.

Since the soundcard sample clock and the sync sample clock differs
verry litttle in frequency the difference can be compensated for by
duplicating or removing samples. I made some tests, even if one have
to do it for every 100 samples it is impossible to hear, if more often
the distorsion can be removed by applying a short lowpass filter with
a cutofff of about 0.95 (relative frequency).

I will continue on the new sound library in this week, I will allow for
external sample clock in the design.

> 
> A'rpi / Astral & ESP-team
> 

//Anders