[FFmpeg-cvslog] r19773 - in trunk/libavformat: seek.c seek.h
Michael Niedermayer
michaelni
Fri Sep 18 14:46:56 CEST 2009
On Fri, Sep 18, 2009 at 08:53:02AM +0300, Uoti Urpala wrote:
> On Fri, 2009-09-18 at 02:04 +0200, Michael Niedermayer wrote:
> > On Thu, Sep 17, 2009 at 07:33:37PM +0200, Ivan Schreter wrote:
> > >>> +static int convert_ts(uint64_t ts, AVRational tb_from, AVRational tb_to)
> > >>> +{
> > >>> + // this algorithm is copied from NUT spec and works only for
> > >>> non-negative numbers
> > >>> + uint64_t ln = (uint64_t) tb_from.num * (uint64_t) tb_to.den;
> > >>> + uint64_t d1 = tb_from.den;
> > >>> + uint64_t d2 = tb_to.num;
> > >>> + return (ln / d1 * ts + ln % d1 * ts / d1) / d2;
> > >>> +}
>
> > > BTW, I simply assumed the formula given in NUT spec is correct, I didn't do
> > > mathematic proof of that. So I hope it is correct :-)
> >
> > the code works, but it seems a little typo sliped through so that 2 variables
> > where exchanged
>
> It's more broken than can be explained with a "little typo".
I didnt want to reply to you but as you keep sending these ridiculous
claims, well, no the code works fine with the typo fixed
> You'd need
> to add more arithmetic to make it work correctly, even with an
> assumption that the scaled times will be below 2^32.
it does not seem so
and i would not say "assumption that the scaled times will be below 2^32"
but rather that the file duration (in case of nut) is less than 130 years
which more clearly shows why i consider your claims ridiculous
that said, there is nothing in the nut format itself that limits it to
130years, its just in the suggested implementation to convert timestamps
> I guess the NUT
> spec implicitly assumed also that the timestamp will a 32-bit number
> (_unscaled_ value)?
Iam not sure how a ascii file can implicitly assume something
> I looked at the NUT spec that computation was copied
> from, and it seems quite vague about the allowed values. There's
> "time_base_denom MUST be < 2^31" but I see nothing similar at all for
> the timestamp and numerator values;
ive added a limit for the numerator for nitpickers sake but i really doubt
one could have ended up with a > 2^31 numerator in reality unless one
intentionally wanted to break demuxers, one amongth other things need a
framerate <1
> OTOH the convert_ts description says
> about calculating timestamp*num*denom/num/denom naively that it "would
> require a 96 bit integer" which seems to assume about 32-bit timestamps
> with 32-bit numerators and denominators.
no
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
Opposition brings concord. Out of discord comes the fairest harmony.
-- Heraclitus
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