fix: reassemble RTP fragments

[swoga]

During my troubleshooting of #502 I noticed that the camera sends fragmented RTP packets, which are not handled correctly and trigger an exception.
I don't know if this has only been happening since Axis OS 11.11 or if it has been happening for a while.

wireshark excerpt:

no.	time		proto	size	info
388	14.018802	RTP	228	PT=DynamicRTP-Type-98, SSRC=0x1F93C2BA, Seq=3799, Time=2365376825, Mark
389	14.057391	RTP	992	PT=DynamicRTP-Type-98, SSRC=0x1F93C2BA, Seq=3800, Time=2365380299, Mark
390	14.107531	RTP	930	PT=DynamicRTP-Type-98, SSRC=0x1F93C2BA, Seq=3801, Time=2365384762, Mark
391	14.185768	RTP	1442	PT=DynamicRTP-Type-98, SSRC=0x1F93C2BA, Seq=3802, Time=2365391782
392	14.186232	RTP	228	PT=DynamicRTP-Type-98, SSRC=0x1F93C2BA, Seq=3803, Time=2365391782, Mark
393	14.323092	RTP	1442	PT=DynamicRTP-Type-98, SSRC=0x1F93C2BA, Seq=3804, Time=2365404094
394	14.323172	RTP	228	PT=DynamicRTP-Type-98, SSRC=0x1F93C2BA, Seq=3805, Time=2365404094, Mark

As one can see the packets with size 1442 have no marker bit set because they were fragmented, the remaining content is received immediately afterwards (see timestamp).

payload of packet no. 391:

<?xml version="1.0" encoding="UTF-8"?>
<tt:MetadataStream xmlns:tt="http://www.onvif.org/ver10/schema">
<tt:Event><wsnt:NotificationMessage xmlns:tns1="http://www.onvif.org/ver10/topics" mlns:tnsaxis="http://www.axis.com/2009/event/topics" xmlns:wsnt="http://docs.oasis-open.org/wsn/b-2" xmlns:wsa5="http://www.w3.org/2005/08/addressing"><wsnt:Topic Dialect="http://docs.oasis-open.org/wsn/t-1/TopicExpression/Simple">tnsaxis:CameraApplicationPlatform/ObjectAnalytics/xinternal_data</wsnt:Topic><wsnt:ProducerReference><wsa5:Address>uri://cfbf96f2-9dc7-437f-aa12-155aacbb0b8f/ProducerReference</wsa5:Address></wsnt:ProducerReference><wsnt:Message><tt:Message UtcTime="2024-10-07T19:52:09.903990Z"><tt:Source></tt:Source><tt:Data><tt:SimpleItem Name="svgframe" Value="&lt;svg xmlns=&quot;http://www.w3.org/2000/svg&quot; version=&quot;1.1&quot; baseProfile=&quot;full&quot; 
xmlns:xlink=&quot;http://www.w3.org/1999/xlink&quot; 
width=&quot;100%&quot; height=&quot;100%&quot; 
viewBox=&quot;-1 -1 2 2 &quot; 
preserveAspectRatio=&quot;none&quot; &gt;
&lt;g transform=&quot;matrix(1 0 0 -1 0 0) matrix(1.0000 0.0000 0.0000 1.0000 0.0000 0.0000 )&quot; &gt;&lt;polygon class=&quot;&quot; points=&quot;0.970,-0.970 -0.480,-0.967 -0.949,-0.678 -0.976,-0.199 -0.866,-0.376 -0.752,-0.356 -0.970,0.970 &quot; style=&quot;fill:#FF0000;fill-opacity:0.2;stroke-opacity:1;stroke:#FF0000;stroke-width

payload of packet no. 392:

:2.5px;vector-effect:non-scaling-stroke" />
&lt;/g&gt;&lt;/svg&gt;"/></tt:Data></tt:Message></wsnt:Message></wsnt:NotificationMessage></tt:Event></tt:MetadataStream>

[Kane610]

Awesome! I'll get back to you during the weekend, you can start by adding a test that covers this situation

[swoga]

added a test!

I had to adapt an existing test, because the dummy value 0123456789ABCDEF was used as data and therefore failed.
I replaced it with a "minimal RTP header" (zeros and only set the position of the RTP marker bit).

[Kane610]

Great!

[Kane610]

I will publish a release tonight

If you see more improvements don't hesitate to to contribute <3

[Kane610]

Release is out, will you publish a PR for home assistant @swoga

[swoga]

Yes, I am happy to do it!