strange pts dts when using v4l2src with raspberry pi camera module

[Nicolas Dufresne]

Le mar. 23 oct. 2018 09 h 27, nucleus_wind <felixjojo199 at gmail.com> a
écrit :

> Hi all,
>
> My setup a raspberry pi 3 with pi camera module listed here:
>
> https://www.amazon.com/Raspberry-Pi-Camera-Module-Megapixel/dp/B01ER2SKFS/ref=sr_1_3?ie=UTF8&qid=1540276869&sr=8-3&keywords=raspberry+pi+camera+module&dpID=41ocSRel7eL&preST=_SY300_QL70_&dpSrc=srch
>
> My pipeline looks like following:
> `gst-launch-1.0 v4l2src do-timestamp=TRUE device="/dev/video0"
> extra-controls="foo,h264_profile=0" !
> video/x-h264,stream-format=byte-stream,alignment=au,width=640,height=480 !
> h264parse ! video/x-h264,stream-format=avc,alignment=au,profile=baseline !
> appsink`
> But I coded it up as a gstreamer application so that I can print out the
> dts
> and pts for every frame.



> The following is the output from my gstreamer application:
>
>
> I set the "is header" and "isKey" base on GST_BUFFER_FLAG_IS_SET(buffer,
> GST_BUFFER_FLAG_HEADER) and  !GST_BUFFER_FLAG_IS_SET(buffer,
> GST_BUFFER_FLAG_DELTA_UNIT) for each frame buffer.
>
> My questions are:
> - why are the dts greater than pts? It seems to be the effect of
> do-timestamp=TRUE. If I remove do-timestamp=TRUE, the dts seems to come
>


Using do-timestamp with v4l2src will result in invalid (dts > pts). You
should leave the default, which will derive the hw timestamp to pts and
leave the dts to none.

straight from the driver. The dts starts at 0 and increments by 33333333 for
> every frame. The pts still get synced but pts are greater than dts for all
> frames.
> - why aren't pts == dts for key frames?


There should be no dts from v4l2src because it's not supported by drivers.
For H264, be aware that pts == dts on B frames (not I frames), when
B-Frames are enabled.

They dont equal each other whether I
> set do-timestamp=TRUE or not. I think I have disabled B frames by setting
> h264 profile to baseline which should enforce pts == dts for key frames.
>

v4l2src does not implement h264 profile negotiation. If this driver
supports it now, then contributions are welcome of course.


> I'm new to gstreamer and I'm trying to get an understanding of what is
> going
> on here. Any help is really appreciated.
>
> Thanks
>
>
>
>
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