Re: [FFmpeg-devel] [PATCH] avcodec/amfenc: Fix for windows imprecise sleep

[Mark Thompson <sw@jkqxz.net>]

On 16/10/2023 10:13, Evgeny Pavlov wrote:
> This commit reduces the sleep time on Windows to improve AMF encoding
> performance on low resolution input videos.
> This fix is for Windows only, because sleep() function isn't
> very accurate on Windows OS.
> 
> Fix for issue #10622
> 
> Signed-off-by: Evgeny Pavlov <lucenticus@gmail.com>
> ---
>   libavcodec/amfenc.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/libavcodec/amfenc.c b/libavcodec/amfenc.c
> index 061859f85c..0c95465d6e 100644
> --- a/libavcodec/amfenc.c
> +++ b/libavcodec/amfenc.c
> @@ -770,7 +770,11 @@ int ff_amf_receive_packet(AVCodecContext *avctx, AVPacket *avpkt)
>           if (query_output_data_flag == 0) {
>               if (res_resubmit == AMF_INPUT_FULL || ctx->delayed_drain || (ctx->eof && res_query != AMF_EOF) || (ctx->hwsurfaces_in_queue >= ctx->hwsurfaces_in_queue_max)) {
>                   block_and_wait = 1;
> +#ifdef _WIN32
> +                av_usleep(0); //Sleep() is not precise on Windows OS.
> +#else
>                   av_usleep(1000);
> +#endif
>               }
>           }
>       } while (block_and_wait);

Wasting lots of power by spinning on a CPU core does not seem like a good answer to this problem.  (I mean, presumably that is why Windows isn't honouring your request for a short sleep, because it wants timers to have larger gaps to avoid wasting power.)

Why is there a sleep here at all, anyway?  An API for hardware encoding should be providing a way for the caller to wait for an outstanding operation to complete.

Thanks,

- Mark
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