libavcodec shouldn't advertise hardware specific codecs on systems without such hardware

[Dave Plater]

Summary of the bug: >= ffmpeg-3.3: browser won't play youtube video due to advertised h264_cuvid codec being present but not functional.
How to reproduce:
See ​https://bugzilla.suse.com/show_bug.cgi?id=1041794
When using the official crippled avcodec in openSUSE the h264 codec is not present but the h264_cuvid decoder is advertised and the browser engine attempts to use this codec on no nvidia hardware. I have fixed this by disabling cuvid and cuda in the build. I can most probably enable cuda and just disable cuvid as a user with the crippled avcodec would most likely have the uncrippled version from Packman installed and I can confirm that when the normal h264 is available it is used and the youtube video works.
There is also an anomaly that I can't explain which was also fixed when I disabled cuvid and cuda relating to gstreamer's libav see:
​https://bugzilla.suse.com/show_bug.cgi?id=1039163
Unfortunately I can't reproduce that bug as I have intel graphics but I have two low end nvida cards which I will try at a later stage, when I have time to risk breaking my system.
In that bug (1039163) the user has 4 different computers with nvidia graphics and gstreamer's libav timed out when attempting to read mpeg-1 and 2 video, I'm not sure yet if the user has official nvidia drivers or the kernel's nouveau drivers in use.

[Carl Eugen Hoyos]

We know that Opensuse is abusing the name of our libraries, there is nothing we can do about it.
Please do not mix different issues in one ticket.

[Dave Plater]

I'm confused, what abuse of libavcodec's name are you referring to? If there is naming abuse I will fix it. Full build log for ffmpeg in question:
​https://build.opensuse.org/build/openSUSE:Leap:42.2:Update/standard/x86_64/ffmpeg.6675/_log
I apologize for the second issue, I was merely asking for advice as to whether there was a relation between the two. Possibly another openSUSE maintainer was less than polite in the past?

[Timo R.]

This is more a bug in the application using the libraries.
libavcodec can't possibly know in advance which hw codecs are supported on a system, and it's up to the individual application to do a proper fallback.

[Dave Plater]

This is more of a feature request for runtime detection of the gpu that would solve the browsers issues. One has apparently acknowledged the problem but WONTFIX. The other issue seems to be gstreamer's problem that is fixed in later releases. What ffmpeg version introduced cuvid decoders?

[Hendrik]

The cuvid decoder already has runtime detection, if you try to use it and its not supported, it'll instantly fail and the application knows to use something else.

[Dave Plater]

The gst-libav issue is fixed in their git. Both issues were exposed by ffmpeg >= 3.3 enabling cuvid by default.