[Bug 783829] omxh264enc: unclear 'interval-intraframes' property

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=783829

--- Comment #5 from Guillaume Desmottes <gdesmott at gnome.org> ---
I did some testing on the pi and the 'interval-intraframes' property on the
omxh264enc element.
The default value of config_avcintraperiod.nPFrames is 60 which matches the
observed GOP pattern. But changing it doesn't seem to have any influence, we
always get 60 delta between key frames, regardless of its value.

I tried using OMX_VIDEO_PARAM_AVCTYPE.nPFrames as well and it doesn't seem to
affect the GOP pattern either.
Changing OMX_VIDEO_PARAM_AVCTYPE.nBFrames doesn't seem to change it either.

Actually this property and those OMX settings have absolutely 0 impact. I tried
various "videotestsrc ! omxh264enc ! filesink" pipelines with different
settings and the generated file was always exactly the same.
Which is weird because this property seems to have been added for the pi:
https://cgit.freedesktop.org/gstreamer/gst-omx/commit/?id=e55bf0a4c5d5936cd45c377d3369721bd140ce58

But what DOES work is the OMX_IndexConfigBrcmVideoIntraPeriod defined in the
doc as "OMX_IndexConfigBrcmVideoIntraPeriod".

So my suggestion would to keep the 'interval-intraframes' property and allow
platform specific implementation. We'd use OMX_IndexConfigBrcmVideoIntraPeriod
on the pi.
I'm not sure for the default implementation:
- OMX_VIDEO_CONFIG_AVCINTRAPERIOD.nPFrames (current) ?
- OMX_VIDEO_CONFIG_AVCINTRAPERIOD.nPFrames ?
- both ?
- none (enable the property only on platform it's been tested) ?

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