[FFmpeg-devel] udp.c comments/thoughts

Michael Niedermayer michaelni at gmx.at
Wed Jan 15 21:07:52 CET 2014

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

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