[FFmpeg-devel] udp.c comments/thoughts

[Roger Pack]

On 3/22/14, Michael Niedermayer <michaelni at gmx.at> wrote:
> 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

And another small docu patch, FWIW.
Thanks!
-roger-
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