[FFmpeg-devel] [PATCH] configure: autodetect OpenCL headers and ICD loader

[Gupta, Maneesh]

> -----Original Message-----
> From: ffmpeg-devel-bounces at ffmpeg.org [mailto:ffmpeg-devel-
> bounces at ffmpeg.org] On Behalf Of Hendrik Leppkes
> Sent: Monday, June 08, 2015 1:00 PM
> To: FFmpeg development discussions and patches
> Subject: Re: [FFmpeg-devel] [PATCH] configure: autodetect OpenCL headers
> and ICD loader
> 
> On Mon, Jun 8, 2015 at 5:53 AM, Gupta, Maneesh
> <Maneesh.Gupta at amd.com> wrote:
> >> -----Original Message-----
> >> From: ffmpeg-devel-bounces at ffmpeg.org [mailto:ffmpeg-devel-
> >> bounces at ffmpeg.org] On Behalf Of James Almer
> >> Sent: Thursday, May 28, 2015 10:06 AM
> >> To: FFmpeg development discussions and patches
> >> Subject: Re: [FFmpeg-devel] [PATCH] configure: autodetect OpenCL
> >> headers and ICD loader
> >>
> >> On 28/05/15 12:28 AM, Gupta, Maneesh wrote:
> >> > Attached is a patch that enables configure to autodetect the
> >> > presence of
> >> OpenCL headers and ICD loader. If the necessary headers are found,
> >> the OpenCL infrastructure compilation is enabled as well. Note that
> >> this does not modify the runtime behavior in any way. Execution of
> >> the OpenCL code path still requires the user to explicitly enable it.
> >> >
> >> > Please review the patch and share your comments on the same.
> >> >
> >> > - Maneesh
> >>
> >> I personally don't agree OpenCL should be autodetected.
> >>
> >> Currently, only the so called "system" libs are autodetected (zlib,
> >> iconv, pthreads, the like). Open*L, decoding/encoding libraries, and
> >> other miscellaneous libraries are enabled only if explicitly requested.
> >> If we enable one by default, then there's no argument against
> >> enabling every other as well ("Why this one but not that other
> >> one?"), and suddenly default builds become bloated and automated
> >> scripts get potentially broken until adapted.
> >>
> >> Lets keep default builds as lightweight as possible, and allow people
> >> to explicitly enable the functionality they require.
> >
> > [Gupta, Maneesh] Apologize for the delayed response. However grep'ing
> the string "autodetect" in the configure script throws up several "non-
> system" libs including D3D11VA, DXVA2, VAAPI, VDA, VDPAU, sdl. Why are
> they turned on by default? Several of these non-system libs enable use of
> hardware acceleration. OpenCL is similar in nature with a key difference that
> it is more platform/OS agnostic and can run on both CPU as well as GPU.
> 
> Most of those don't link against any library, ie. like DXVA2, it doesn't add any
> extra link dependencies which are not system libraries, so the resulting build
> is still perfectly portable.
> For the few exceptions that do add link deps, we suffer for that enough, we
> don't need any more "exceptions".
> 
> - Hendrik

[Gupta, Maneesh] The OpenCL code only links against the ICD loader. Also x264 enables OpenCL code by default and the build is perfectly portable as far as I have seen. I don't see how that is not possible in the case of ffmpeg.