gstclock and absolute time

Tue Jun 26 08:59:42 PDT 2012

Dear Josh,

I want just to add a bit of info. I'm trying to understand how to
correlate data from signal "handle-sync"
(http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-good-plugins/html/gst-plugins-good-plugins-gstrtpjitterbuffer.html#GstRtpJitterBuffer-handle-sync)
 of GstRtpJitterBuffer and "stats" of rtpsession but I really don't
understand what base-time is....

This is what I get from GstRtpJitterBuffer "handle-sync" signal:

application/x-rtp-sync, base-rtptime=(guint64)2490599386,
base-time=(guint64)137714729, clock-rate=(uint)90000,
sr-ext-rtptime=(guint64)2491725922,
sr-buffer=(buffer)80c800069af6cadbd39457a5e959817b9484b862000003ed0010b1da81ca000c9af6cadb0116726f6f7440616f63632d617869732d646f6d656f6c640204726f6f7406094753747265616d6572000000;

and at the same time from rtpsource "stats":

application/x-rtp-source-stats, ssrc=(uint)2599865051,
internal=(boolean)false, validated=(boolean)true,
received-bye=(boolean)false, is-csrc=(boolean)false,
is-sender=(boolean)true, seqnum-base=(int)-1, clock-rate=(int)90000,
rtp-from=(string)192.168.3.27:50088,
rtcp-from=(string)192.168.3.27:50089, octets-sent=(guint64)0,
packets-sent=(guint64)0, octets-received=(guint64)1155650,
packets-received=(guint64)1060, bitrate=(guint64)703428,
packets-lost=(int)0, jitter=(uint)83, have-sr=(boolean)true,
sr-ntptime=(guint64)15245907008652149115, sr-rtptime=(uint)2491725922,
sr-octet-count=(uint)1094106, sr-packet-count=(uint)1005,
sent-rb=(boolean)true, sent-rb-fractionlost=(uint)0,
sent-rb-packetslost=(int)0, sent-rb-exthighestseq=(uint)18120,
sent-rb-jitter=(uint)97, sent-rb-lsr=(uint)1470108312,
sent-rb-dlsr=(uint)337017, have-rb=(boolean)false,
rb-fractionlost=(uint)0, rb-packetslost=(int)0,
rb-exthighestseq=(uint)0, rb-jitter=(uint)0, rb-lsr=(uint)0,
rb-dlsr=(uint)0, rb-round-trip=(uint)0;

Does anybody know how to obtain the damn time reference  from
sr-rtptime/sr-ntptime to pipeline "absolute time" (aka the  one
defined here http://cgit.freedesktop.org/gstreamer/gstreamer/tree/docs/design/part-synchronisation.txt)?

TIA,

pz

2012/6/26 Pazzo Da Legare <pazzodalegare at gmail.com>:
> Dear Josh,
>
> Thank you very much for your links.
>
> I thought I couldn't find the right parameter to instruct rtspsrc to
> propagate the time downstream (or better to say to use the rtsp source
> time as clock reference) I was more than sure that it would have been
> possible, but now you confirm that a "crazy" idea to manage sr-message
> is the only (known) way to extract source reference: I'm trying to
> follow exactly the same approach trying to extract absolute time from
> rtspsrc and send a metadata event (GST_EVENT_TAG) through my pipeline.
> The point is how to correlate internal absolute time (what you can get
> with gst_clock_get_time()) and ntptime of RTCP protocol without
> _error_ (i.e. taking into account source->rtspsrc transmission time)?
>
> I can intercept RtpSession information but I have no way to relate
> (sr-ntptime, sr-rtptime) with the time (internal absolute time) of the
> frame they are referring to. Any clue?
>
> BR,
> pz
>
>
>
>
> 2012/6/26 Josh Doe <josh at joshdoe.com>:
>> On Tue, Jun 26, 2012 at 6:06 AM, Pazzo Da Legare
>> <pazzodalegare at gmail.com> wrote:
>>> Dear all,
>>>
>>> How can I convert gst_clock_get_time() value in an absolute time (with
>>> year, month, day, ....). I'm playing with an rtsp camera, using
>>> rtspsrc, and I would like to retrieve absolute time (ntp stream time)
>>> across my pipeline. Is there an easy way to do that?
>>>
>>> from element's clock time now  (=Tue Jun 26 12:03:34 CEST 2012) I get
>>> something like:
>>>
>>> 6112256969101111
>>>
>>> and it contains a bunch of thousands of seconds....
>>>
>>> I'm a little bit puzzled.
>>
>> gst_clock_get_time() will just give you a monotonically increasing
>> integer. Subtracting the base time from that will give you the stream
>> time:
>> http://gstreamer.freedesktop.org/data/doc/gstreamer/head/manual/html/chapter-clocks.html
>>
>> If you're talking about the ISO 8601 timestamps that indicate the
>> absolute UTC time, this doesn't appear to be implemented currently:
>> http://cgit.freedesktop.org/gstreamer/gst-plugins-base/tree/gst-libs/gst/rtsp/gstrtsprange.c#n249
>> http://tools.ietf.org/html/rfc2326#page-18
>>
>> A few issues. Not all servers support absolute time ranges. You can
>> only get an absolute time if you requested the range in the same
>> format, so rtspsrc would need to be given this information. Or you
>> could extract a time range from SDP. Either way, you'd need a way to
>> get the time to the application.
>>
>> This last part is what I'm interested. For now I'm sending a
>> GST_TAG_DATE_TIME event to indicate the start time of the stream, so a
>> buffer absolute time can be calculated from this absolute time and the
>> stream time. If there's a better way (GstMeta?) then I'd like to hear
>> it.
>>
>> -Josh
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