[FFmpeg-devel] udp.c comments/thoughts

[Michael Niedermayer]

On Fri, Mar 21, 2014 at 05:55:09PM -0600, Roger Pack wrote:
> On 1/15/14, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Wed, Jan 15, 2014 at 12:59:27PM -0700, Roger Pack wrote:
> >> On 1/6/14, Andrey Utkin <me at andrey-utkin.pp.ua> wrote:
> >> > On 06.01.2014 21:37, Roger Pack wrote:
> >> >> On 1/6/14, Roger Pack <rogerdpack2 at gmail.com> wrote:
> >> >>> Hello.  I noticed that in udp.c sometimes (with pthread cancel
> >> >>> enabled) it says "Part of datagram lost due to insufficient buffer
> >> >>> size" (I think what it meant to say is due to insufficient read
> >> >>> request size?)
> >> >
> >> > No principal difference. But we could somewhat improve log message with
> >> > user-friendly advice, if possible. I haven't check deeply this at the
> >> > moment.
> >> >
> >> >>> Also it's quite confusing that fifo_size is in multiples of 188.
> >> >>> Unless you an MPEG engineer, nobody anticipates this.  I might
> >> >>> suggest
> >> >>> adding another setting of "fifo_size_bytes" or something so that
> >> >>> people realize there's a difference.
> >> >
> >> > Yep, confusing. Historical issue.
> >> > "fifo_size_bytes" sounds a sort of humiliating for this proper option,
> >> > comparing to ugly "fifo_size" option taking multiples of 188. Maybe
> >> > some
> >> > more "respectful" name could be found?
> >> >
> >> >>> Also I've noticed that the default RECV buffer size is 64K by default
> >> >>> for udp packets.  I might suggest increasing this substantially, as
> >> >>> this is far too little for many streams, and the OS can typically
> >> >>> handle far higher (1M-10MB at least).
> >> >
> >> > Are there any official documents regulating allowed UDP packet sizes?
> >> > Or
> >> > you tell us what happens to work with current Linux? Maximum which i
> >> > have seen in nature was 0xffff bytes via IPv4 loopback interface.
> >>
> >> The default reported by Ubuntu 12.10 is 212992 which I believe you
> >> divide by 2 to get the "real" value, 106496.
> >> This means that currently, by default, FFmpeg is actually changing the
> >> buffer size to *lower* the default (since it sets it to 64KB).  Which
> >> may not be desirable.
> >>
> >> I could see changing the default to 128KB instead, or possibly adding
> >> extra/more logic so that the default is MAX(current, 64KB), thought?
> >
> > if you send a patch that sets it to MAX(current, 1MB) then ill
> > apply it
> 
> OK here's a couple followup patchs as well.  One adds a warning if
> people don't realize they're not getting what they requested for
> buffer_size. FWIW.  The other is docu.

applied
i left the debug av_log in there though

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Rewriting code that is poorly written but fully understood is good.
Rewriting code that one doesnt understand is a sign that one is less smart
then the original author, trying to rewrite it will not make it better.
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