[FFmpeg-devel] pipeline multithreading

[Timothy Gu]

On Mon, Nov 24, 2014 at 3:35 AM, Daniel Oberhoff
<danieloberhoff at gmail.com> wrote:
> Hi,
>
> From what I gather the filter graph is utilizing modern multicores by
> “striping” where filters support it, i.e. an image is divided in stripes
> and the filter gets called in separate threads for separate stripes.

In FFmpeg we call it slice threading.

> I was wondering if there is or will be pipeline multuthreading, i.e.
> with a setup such as
>
> inout -> filter1 -> filter2 -> output
>
> some threads processing frame n in the output (i.e. encoding),
> other threads procesing frame n+1 in filter2, others processing frame
> n+2 in filter1, and yet others processing frame n+3 decoding. This
> way non-parallel filters can be sped up, and diminishing returns for
> too much striping can be avoided. With modern cpus scaling easily
> up to 24 hardware threads I see this as neccessary to fully utilize the
> hardware.

We call it "frame threading." There are some decoders that already support it.

>
> Is this already done? Or are there plans? If it is not done, how much
> more work is it? Could I help (not promising much, but I may find time,
> especially as this limits us…).

If the filter is independent of past and future frames then it is
pretty easy (just like the "intra-only" decoders). For other ones I am
not so sure. Clément knows more about it.

Timothy