[FFmpeg-devel] Discuss: Improved hardware acceleration support

Hendrik Leppkes h.leppkes at gmail.com
Fri Oct 31 19:06:28 CET 2014

On Fri, Oct 31, 2014 at 5:59 PM, wm4 <nfxjfg at googlemail.com> wrote:

> On Thu, 30 Oct 2014 20:31:17 -0500
> Rodger Combs <rodger.combs at gmail.com> wrote:
> > libavcodec currently has support for hardware-accelerated decoding, but
> no support for encoding, and libavcodec+libavfilter+ffmpeg provide no
> support for a decode->filter->encode pipeline that doesn't involve copying
> buffers back and forth from the video card and cutting out a significant
> amount of the gain provided by using hardware acceleration to begin with.
> It'd be useful to provide a way to leave buffers on the GPU when possible,
> and copy back and forth only when using a filter that can't be done on the
> GPU.
> > Some filters could even be run without copying back and forth; for
> instance: scaling (for some scalers), overlays, cropping,
> drawtext/subtitles (the drawing component, anyway), deinterlacing, trim,
> and some post-processing could likely be done for a number of GPUs
> relatively easily, and others could likely also be done with additional
> work.
> > This would probably require significant changes to AVFrame, various
> lavc/lavfi structs and APIs, and ffmpeg.c, but it could likely produce
> significant improvements in speed and power consumption when using systems
> that can support a full decode->filter->encode pipeline on the GPU.
> >
> > Thoughts on feasibility and/or implementation details?
> It would be pretty simple.

Really? :)

Every HW accel uses its own special format, how do you ever want to make
lavfi be capable of handling those all? It would be a nightmare of HW-API
specific stuff, and considering practically none of the software filtering
code can be reused anyway, hardly worth trying to shoehorn that into lavfi
All the pieces are already in place for an application to do this itself
for the one or two HW APIs it cares about, however, just the generic case
is an absolute nightmare.

- Hendrik

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