Metrics from the latency subsystem

[Vineet Krishnan]

Hi Nicholas,

Thanks for the explanation, makes sense.

And yes, I was using the zerolatency tuning for the x264 element 😀

Thanks!
Vineet

On Thu, Oct 14, 2021 at 6:53 PM Nicolas Dufresne <nicolas at ndufresne.ca>
wrote:

> Hi Vineet,
>
> Thanks for your question, see answers below.
>
>
> Le jeu. 14 oct. 2021 19 h 15, Vineet Krishnan via gstreamer-devel <
> gstreamer-devel at lists.freedesktop.org> a écrit :
>
>> Hello,
>>
>> I'm looking into the Tracing subsystem
>> <https://gstreamer.freedesktop.org/documentation/additional/design/tracing.html?gi-language=c#try-it> to
>> measure processing latency in our gstreamer pipeline. On running the
>> generated file through gst-stats, I get the following output -
>>
>>
>> Latency Statistics:
>>     0x7fd35e827ce0.audiotestsrc0.src|0x7fd35c813290.rtmpsink0.sink:
>> mean=0:00:00.059332305 min=0:00:00.003686000 max=0:00:00.782444000
>>     0x7fd35d0082e0.videotestsrc0.src|0x7fd35c813290.rtmpsink0.sink:
>> mean=0:00:00.043311752 min=0:00:00.003628000 max=0:00:00.797304000
>>
>> Element Latency Statistics:
>>     0x7fd35d030190.capsfilter0.src: mean=0:00:00.000519092
>> min=0:00:00.000263000 max=0:00:00.001867000
>>     0x7fd35e830240.audiomixer0.src: mean=0:00:00.023331131
>> min=0:00:00.001518000 max=0:00:00.774963000
>>     0x7fd35e82f4d0.audioconvert0.src: mean=0:00:00.000393081
>> min=0:00:00.000143000 max=0:00:00.011368000
>>     0x7fd35d034150.x264enc0.src: mean=0:00:00.003406024
>> min=0:00:00.002231000 max=0:00:00.006731000
>>     0x7fd35e82fc70.faac0.src: mean=0:00:00.000625431
>> min=0:00:00.000355000 max=0:00:00.003427000
>>     0x7fd35e830540.mux.src: mean=0:00:00.036701334 min=0:00:00.000177000
>> max=0:00:00.792271000
>>
>>
>> I couldn't find a definitive explanation of these numbers by searching
>> online, so I wanted to verify if my understanding is correct.
>>
>> For the line
>>
>> 0x7fd35e827ce0.audiotestsrc0.src|0x7fd35c813290.rtmpsink0.sink:
>> mean=0:00:00.059332305 min=0:00:00.003686000 max=0:00:00.782444000
>>
>> Does it mean that there was a mean latency of 0.059s and a max latency of
>> 0.78s to propagate a buffer from the audiotestsrc to the rtmpsink? If yes,
>> would this represent the end-to-end processing latency of this source->sink
>> path?
>>
>
> The reported latency includes all form of latency. The processing latency
> is usually estimated by subtracting the reported latency. Though, in case
> of tsdemux, which has over 700ms latency declared, it will only effectively
> have this latency during the period needed to figure-out timestamp
> information, hence the much lower mean latency.
>
>
>> Similarly, for the element latency statistics -
>>
>> 0x7fd35d034150.x264enc0.src: mean=0:00:00.003406024 min=0:00:00.002231000
>> max=0:00:00.006731000
>>
>> Does it mean that the x264enc is adding 0.006s processing latency?
>>
>
> In this case, I can only suppose you are using x264 zerolatency tuning.
> And indeed, with that context this number will be purely the processing
> time.
>
>
>>
>> Thanks!
>>
>
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