Re: Get camera timestamp from rtsp stream.

Thu Jul 20 17:06:15 UTC 2023

Hi, Anand!

Thank you so much for reply!

> If the camera does not support any extra timing as described above, then I am not sure how to get the exact actual capture timestamp of the frame from the camera.

Sure, camera has to support this. I forgot to mention it but it was assumed.
For now it seems I found solution described here —  https://stackoverflow.com/a/75799182/241446
In my case it was enough —  https://gist.github.com/sharov-am/869409461f60f47c5772f741a3b31dbd

What confuse me when I tried before (whilde debugging) is that it not always returns timestamp,
and there is a reason for this — there is special RTCP packet which occurs once in few a seconds
and provide precise info. I believe once it is obtained there would be more or less precise camera time.
Still I have to read more (including your link provided above) because I’m not sure what happens if
for some time we miss these RTCP packets. Say if we only obtained it once in the beginning of session,
and we (capture) stream for hours, what will GetReferenceTimestampMeta() return in this case?
If for some reason, GetReferenceTimestampMeta starts return null (ts ==0) we should fallback on other
mechanism, probably one you described (thank you again!!!).

Still I have few questions maybe for separate topic:
*  exact and precise method to obtain ts for keyframe of a newly created file. My approach above simply takes latest ts value. I don’t think it is very critical, hopefully there are should be some nanoseconds difference, but still it would be nice to be sure that I have ts for needed buffer and not ts for some transient buffer (frame for prev. mp4 file, for example)
*  Is it possible to provide meta information for each frame, namely give each frame it’s timestamp? There is smth like GstMeta, but I’m not sure there is examples to provide meta info for each frame. Maybe use Identity element?
Thank you very much for your time and help, Anand!

>Среда, 19 июля 2023, 21:23 +03:00 от Anand Sivaram <aspnair at gmail.com>:
> 
>I think Jeff was talking about this one.
>
>https://www.onvif.org/specs/stream/ONVIF-Streaming-Spec.pdf
>6.3 section RTP header extension
>That would require the camera to support it.
>
>@Anton - got your requirement.  If the camera does not support any extra timing as described above, then I am not sure how to get the exact actual capture timestamp of the frame from the camera.
>
>We can try to derive it based on RTP timestamp only.
>- With splitmuxsink and "format-location" callback, get the system time - for example time.time() equivalent of python - on the RTSP client and mark it in the MP4 filename.
>- RTP clock gets incremented by 90000Hz and if it is 30fps then 3000 in every frame.
>- Since you are using 3sec MP4, then there would be 90 frames, 270000 in RTP timestamp increase.
>- Now run the recording for some time, correlate the actual time observed on "format-location" and the RTP timestamp and compute the jitter and see if it is sufficient.
>
>This method has one assumption - that is the network jitter is low and manageable..  If the camera and RTSP client are on the same network - preferably wired - then jitter would be a few msec only, then that could be less than 10% of interframe time of 33msec.
>
>Anyway, would be happy to hear better suggestions from experts.
>
>Thanks and Regards
>
>Anand  
>On Wed, 19 Jul 2023 at 22:56, Антон Шаров < sharov_am at mail.ru > wrote:
>>Hi, Anand!
>> 
>>Thank you so much for your reply!
>> 
>>The thing is I don’t need RTP, I need exact camera(server) capture time of a frame.
>>Ideally, I need capture time for each frame, but probably for some keyframe of mp4 file
>>(first frame of this video file?) would be ok also. I’m trying to use my custom appsink,
>>smth like
>>appSink.NewSample += AppSink_NewSample;
>> 
>>splitmuxsink["sink"] = appSink;
>>splitmuxsink["max-size-time"] = 3000000000;
>>splitmuxsink["async-finalize"] = false;
>> 
>>private static void AppSink_NewSample(object o, NewSampleArgs args)
>>        {
>>            if (o is AppSink aps)
>>            {
>>                var sample = aps.PullSample();
>>                var buf = sample.Buffer;
>>                buf.Map(out var info, MapFlags.Read);
>>                var ts = buf.GetReferenceTimestampMeta();// !!!!!!
>>                buf.Unmap(info);
>>            }
>>        }
>>I don’t quite understand whether it is possible to have needed (3 sec. in this case) mp4 file in
>>whole buffer, for which I can use GetReferenceTimestampMeta() which return me timestamp
>>for this buffer (hence for  whole file, hence for keyframe). But on practice with my custom sink
>>I got some weired chunks in buffer and  GetReferenceTimestampMeta returns null (not null exactly,
>>but some useless info where needed timestamp = 0).
>> 
>>I believe this ideal approach won’t work (because appsink is not seekable), but at least it looks like
>>desired solution.
>> 
>>In case of default sink (filesink), I need
>>*  change file name, which somehow seems to be possible but is buggy on .net library, but at least it is seems to possible;
>>*  get timestamp of the first frames (buffer) of newly created file. Ideally I would like to name newly created file with timestamp_value.mp4.
>> 
>> 
>>  
>>>Среда, 19 июля 2023, 12:37 +03:00 от Anand Sivaram < aspnair at gmail.com >:
>>> 
>>>Hello Anton,
>>> 
>>>The RTSP media is coming as separate RTP streams for each video and audio.  They must be having only usual RTP parameters like timestamp, sequence number and payload type.
>>>That too RTP timestamps are initialized randomly as per standard, so the timestamps on video and audio streams have no relation at all.
>>>If you are planning to read the time using some OCR software from the video frame, then you will have to decode H.264 and the typical granularity is 1sec.
>>> 
>>>Are you using the "format-location" callback signal in splitmuxsink with which you can generate custom filenames with timestamp and any prefix.  It is not available on gst-launch, but it is definitely available on C and Python.
>>> 
>>>Thanks and Regards
>>> 
>>>Anand
>>>   
>>>On Mon, 17 Jul 2023 at 15:36, Антон Шаров via gstreamer-devel < gstreamer-devel at lists.freedesktop.org > wrote:
>>>> 
>>>>Hi.
>>>> 
>>>>I’m given rtsp stream from camera, where each frame has capturing timestamp.
>>>>Connection strin looks like rtsp://{usr}:{pwd{@ip_addr/onvif/media?profile=Profile1
>>>>I need to store this data for some time and provide search access for this data, either return closest (exact) frame for provided timestamp or return mp4 file which containts this closest frame. My first pipeline is   rtsp ! h264depay ! h264parse ! splitmuxsink  location=… max-time-size=10seconds (for example), when I save new file via splitmuxsink, I’m some how need to get camera timestamp
>>>>for first frame of video (or key frame) and maybe store this mp4 file as timestamp.mp4 (or save ts for later in some db, for example).
>>>> 
>>>>Other approach is to use jpegenc and to store each frame with it’s timestamp, but I don’t know how to obtain timestamp for jpeg buffer (rtsp ! decodebin ! jpegenc ! appsink). But  I assume  that this won’t be effective solution in terms of CPU and storage usage, and better to store mp4 files.
>>>> 
>>>>So, in both cases I don’t know how to get reference-timestamp-meta for needed buffer.
>>>> 
>>>>Can someone help me? 
>>>> 
>>>>PS: I use C# wrapper, namely gstreamer-sharp, but I don’t think it is relevant for this problem.
>>>> 
>>>>Thanks in advance.
>>>> 
>>>>--
>>>>С Уважением,
>>>>Шаров Антон
>> 
>> 
>>--
>>С Уважением,
>>Шаров Антон
>> 

--
С Уважением,
Шаров Антон

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