[FFmpeg-devel] udp.c comments/thoughts

[Michael Niedermayer]

On Wed, Jan 15, 2014 at 09:07:52PM +0100, Michael Niedermayer 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

or maybe rather MAX(current, THREADS ? 64KB : 1MB)


> apply it
> 
> [...]
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