[FFmpeg-devel] [PATCH] fftools/ffplay: use SDL_WaitEvent instead of SDL_PeepEvents while paused

[Marton Balint]

On Fri, 10 Nov 2023, Bolshoy Toster wrote:

> Currently, when ffplay is paused, it still constantly polls for events at the
> REFRESH_RATE (100 times per second). This leads to a high (5-10% on the 
> latest
> commit, using SDL2 2.28.5-1) CPU usage, when it should be idle.
>
> This commit changes this behaviour to use SDL_WaitEvent while paused, 
> allowing
> ffplay to use less (0-5% under X11) CPU time while paused on supported 
> platforms
> (windows, X11 and wayland) with SDL versions >=2.0.16.
>
> This has the side effect of only running the refresh loop when there's an 
> event,
> preventing the cursor from being hidden while paused.

Was this always this way? Or upstream SDL changed something making the 
Pump/GetEvent more resource intensive? Polling like 100 times per 
second should not cause 10% cpu usage...

ALso, can this patch be made less intrusive? E.g. changing current code 
around av_usleep(remainig time) to:

if (*remainig_time > 0.0) {
   if (is->paused)
       SDL_WaitEventTimeout(NULL, 100);
   else
       av_usleep()
}

Regards,
Marton

>
> Signed-off-by: bolshoytoster <toasterbig at gmail.com>
> ---
>  fftools/ffplay.c | 31 ++++++++++++++++++++-----------
>  1 file changed, 20 insertions(+), 11 deletions(-)
>
> diff --git a/fftools/ffplay.c b/fftools/ffplay.c
> index d8c69e1..7814589 100644
> --- a/fftools/ffplay.c
> +++ b/fftools/ffplay.c
> @@  -3221,20 +3221,29 @@ static void toggle_audio_display(VideoState *is)
>      }
>  }
>  +static void refresh(VideoState *is, double *remaining_time) {
> +    if (!cursor_hidden && av_gettime_relative() - cursor_last_shown > 
> CURSOR_HIDE_DELAY) {
> +        SDL_ShowCursor(0);
> +        cursor_hidden = 1;
> +    }
> +    if (*remaining_time > 0.0)
> +        av_usleep((int64_t)(*remaining_time * 1000000.0));
> +    *remaining_time = REFRESH_RATE;
> +    if (is->show_mode != SHOW_MODE_NONE && (!is->paused || 
> is->force_refresh))
> +        video_refresh(is, remaining_time);
> +}
> +
>  static void refresh_loop_wait_event(VideoState *is, SDL_Event *event) {
>     double remaining_time = 0.0;
> -    SDL_PumpEvents();
> -    while (!SDL_PeepEvents(event, 1, SDL_GETEVENT, SDL_FIRSTEVENT, 
> SDL_LASTEVENT)) {
> -        if (!cursor_hidden && av_gettime_relative() - cursor_last_shown
>>  CURSOR_HIDE_DELAY) {
> -            SDL_ShowCursor(0);
> -            cursor_hidden = 1;
> -        }
> -        if (remaining_time > 0.0)
> -            av_usleep((int64_t)(remaining_time * 1000000.0));
> -        remaining_time = REFRESH_RATE;
> -        if (is->show_mode != SHOW_MODE_NONE && (!is->paused || 
> is->force_refresh))
> -            video_refresh(is, &remaining_time);
> +    if (is->paused) {
> +        refresh(is, &remaining_time);
> +        SDL_WaitEvent(event);
> +    } else {
>         SDL_PumpEvents();
> +        while (!SDL_PeepEvents(event, 1, SDL_GETEVENT, SDL_FIRSTEVENT, 
> SDL_LASTEVENT)) {
> +            refresh(is, &remaining_time);
> +            SDL_PumpEvents();
> +        }
>      }
>  }
>  -- 2.42.1
>
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