[vlc-devel] [RFC PATCH 01/13] clock: add vlc_clock

[Thomas Guillem]

On Fri, Aug 31, 2018, at 14:36, Zhao Zhili wrote:
> On 8/31/18 5:59 PM, Denis Charmet wrote:
> > Hi,
> > 
> > On 2018-08-29 11:10, Zhao Zhili wrote:
> >> On 2018年06月27日 20:41, Thomas Guillem wrote:
> >>> +static vlc_tick_t main_stream_to_system(vlc_clock_main_t * main_clock,
> >>> +                                       vlc_tick_t pts)
> >>> +{
> >>> +    if (unlikely(main_clock->offset == VLC_TS_INVALID))
> >>> +        return VLC_TS_INVALID;
> >>> +    return (vlc_tick_t) (pts * main_clock->coeff / main_clock->rate 
> >>> + main_clock->offset);
> >>> +}
> >>
> >> I'm afraid int64_t to float to int64_t won't work well as float can
> >> only represent a small integer precisely.
> >> main_clock->offset makes it worse since it isn't uncommon to be a 
> >> large value.
> >>
> >> (vlc_tick_t)(pts * main_clock->coeff / main_clock->rate) + 
> >> main_clock->offset
> >>
> >> may be a little better, but the problem is still there.
> >>
> > 
> > Thanks for the review, it's indeed a very interesting point. It seems 
> > that switching to double might help a lot with that. Any other suggestions?
> > 
> > Regards,
> 
> double should give milliseconds precision at the worst case, but I'm not 
> sure.

Your test confirms that a double will be OK.

> 
> I think the math in AvgRescale is incorrect, in both the master branch 
> and the clock-core branch. I have a patch for it
> 
> clock: fix AvgRescale
> 
> It doesn't make sense in mathematics, but it may have a special meaning 
> I missed. And the function is not used in the clock-core branch, so it 
> doesn't matter anymore if it's finally being removed.

It will and still be used by the input clock, even in the clock-core branch.
We'll rework and probably the input clock for VLC 5.0 when we rework the buffering.

So, I'll probably merge your AvgRescale fix in our clock branch.

> 
> 
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