[AG-DEV] [Sumover-dev] Re: UCL common lib rtp_recv & frame timing

P O'Hanlon p.ohanlon at gmail.com
Fri Jul 30 07:51:48 CDT 2010


Andrew,

When you mentioned that you'd played with the buffer sizes - I assume
you meant the default send/recv socket buffer size (udpbufsize) in
common/src/net_udp.c:291?

Also what sort of bit-rate is 'low bit rate' H.264 at 30fps?

One thought is whether you're sending RTCP packets as well and whether
the hiccups correspond to RTCP packet arrival and associated
processing..?
common/src/rtp.c:1894
(not sure why this should be hitting you so hard unless you've got
some weird RTCP packets..?)

Piers



On 28 July 2010 17:41:41 UTC+2, Andrew Ford <andrew.ford at rit.edu> wrote:
> Hi Rhys,
>
> I've tried calling rtp_recv once with both 10ms and 1ms timeout times (as well as no timeout at all) and it looks like it doesn't make a difference. I also tried changing the system UDP buffer sizes to see if that had any effect, but it doesn't seem to.
>
> --Andrew
>
> 2010/7/27 Rhys Hawkins <rhys.hawkins at anu.edu.au>
>>
>> On Tue, 27 Jul 2010 14:12:37 -0400
>> Andrew Ford <andrew.ford at rit.edu> wrote:
>>
>> >
>> >   timeout.tv_sec = 0;
>> >   timeout.tv_usec = 10000;
>> >   for (int i = 0; i < 1000 && rtp_recv(session, &timeout, _timestamp); i ++) {
>> >
>> >
>> >     timeout.tv_sec = 0;
>> >     timeout.tv_usec = 10;
>> >
>> >   }
>> >
>>
>> Hi Andrew,
>>
>> All that code is doing is a crude version of:
>>
>>  while (elapsed_time < 10ms) {
>>    process incoming packets
>>  }
>>
>> You could try and replace the for loop with just one call to the rtp_recv
>> function, ie:
>>
>>  timeout.tv_sec = 0;
>>  timeout.tv_usec = 10000;
>>  rtp_recv(session, &timeout, _timestamp);
>>
>> and see if that fixes your problem.
>>
>> The code above was to handle an issue with DV decoding in that decoding an
>> entire frame of DV took a certain length of time and during that time the
>> UDP buffer (kernel side) could overflow causing loss of data. I don't think
>> it should be the cause of your problems, but things are pretty foggy that
>> far back in time so it may have other ramifications I've forgotten about.
>>
>> Cheers,
>>    Rhys
>
>
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