rtph264depay - Undefined packet type & NAL unit type 26/27 not supported yet

[Nicolas Dufresne]

Le mercredi 08 janvier 2020 à 20:26 -0500, Bill Klein a écrit :
> I've noticed that some of my rtspsrc pipelines give errors/warnings like the following. Are these fatal? What are the implications?

This is about packet aggretation, or if you prefer, placing multiple
NALs into a single RTP packet. At the moment, we support STAP-A and
STAP-B depayloading. This means aggregating multiple NALs into a
packet, though all NALs will be sharing the same timestamp.

MTAP16 and MTAP24 (this is the one you have hit) are not implemented.
This is about multiple NALs into one packet, but with potentially
multiple timestamps.

https://tools.ietf.org/html/rfc6184#section-5.7
https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/blob/master/gst/rtp/gstrtph264depay.c#L1160

It should not be too hard to implement, I personally never had a server
producing this. It's rare because to produce this, an payloader need to
introduce a significant amount of latency. In GStreamer you will have
to split back NALs per timestamp, as NALs in one buffer are expected to
share the same timestamp.

Now, is it fatal or not, that depends on what the server uses it for.
MTAP is unlikely to contain crucial information like headers, since
those are most of the time followed by an IDR NAL which is usually
quite big. So the efficient aggretation will be STAP-A or B, as all the
content endup having the same timestamp.

So it is quite likely that only some delta slices endup there, which
will create a minor glitch in rendering if it was just dropped. Though,
GStreamer currently post an ERROR message on the bus, and that's meant
to be fatal. I think, best use of your time is to implement the
remaining in the depayloader.

> 
> 2020-01-09T00:29:29.616Z - WARNING - src:rtph264depay13 msg:Could not decode stream. dbg:gstrtph264depay.c(1288): gst_rtp_h264_depay_process (): /GstPipeline:pipeline24/GstRtpH264Depay:rtph264depay13:\nUndefined packet type
> 
> 2020-01-09T00:29:29.627Z - ERROR - src:rtph264depay13 msg:The stream is in the wrong format. dbg:gstrtph264depay.c(1299): gst_rtp_h264_depay_process (): /GstPipeline:pipeline24/GstRtpH264Depay:rtph264depay13:\nNAL unit type 27 not supported yet
> 
> Thanks!
> 
> - Bill
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