[vlc-devel] [PATCH] avcodec VA: reuse the VA if possible disable thread safe buffer pool on WIN32

[Sean McGovern]

Is there a way to blacklist this on machines where we know it doesn't work? Would that be desirable?

-- Sean McG.
-----Original Message-----
From: Steve Lhomme <robux4 at videolabs.io>
Sender: "vlc-devel" <vlc-devel-bounces at videolan.org>Date: Tue, 7 Apr 2015 15:46:08 
To: Mailing list for VLC media player developers<vlc-devel at videolan.org>
Reply-To: Mailing list for VLC media player developers <vlc-devel at videolan.org>
Subject: Re: [vlc-devel] [PATCH] avcodec VA: reuse the VA if possible
 disable thread safe buffer pool on WIN32

On Tue, Apr 7, 2015 at 12:04 PM, Steve Lhomme <robUx4 at videolabs.io> wrote:
> Fixes #11693
> ---
>  modules/codec/avcodec/video.c | 40 +++++++++++++++++++++++++---------------
>  1 file changed, 25 insertions(+), 15 deletions(-)
>
> diff --git a/modules/codec/avcodec/video.c b/modules/codec/avcodec/video.c
> index 381fe62..4e7f32f 100644
> --- a/modules/codec/avcodec/video.c
> +++ b/modules/codec/avcodec/video.c
> @@ -374,7 +374,11 @@ int InitVideoDec( decoder_t *p_dec, AVCodecContext *p_context,
>      i_thread_count = __MIN( i_thread_count, 16 );
>      msg_Dbg( p_dec, "allowing %d thread(s) for decoding", i_thread_count );
>      p_context->thread_count = i_thread_count;
> +# if defined(_WIN32)
> +    p_context->thread_safe_callbacks = false;
> +# else
>      p_context->thread_safe_callbacks = true;
> +# endif

I tried putting a mutex in avcodec where it feeds DXVA with its data.
It was called by multiple threads. Even with that, decoding is still
bogus with Intel Graphics 4000. So I don't see an other way to make it
work with this chipset apart from disabling FF_THREAD_FRAME like we
used to do.

IMO this patch is OK. By default ffmpeg/avplay don't set
thread_safe_callbacks, but that's because they use their own buffer
pools and also check if their functions are used rather than custom
ones.

>      switch( p_codec->id )
>      {
> @@ -396,21 +400,6 @@ int InitVideoDec( decoder_t *p_dec, AVCodecContext *p_context,
>              break;
>      }
>
> -    /* Workaround: frame multithreading is not compatible with
> -     * DXVA2. When a frame is being copied to host memory, the frame
> -     * is locked and cannot be used as a reference frame
> -     * simultaneously and thus decoding fails for some frames. This
> -     * causes major image corruption. */
> -# if defined(_WIN32)
> -    char *avcodec_hw = var_InheritString( p_dec, "avcodec-hw" );
> -    if( avcodec_hw == NULL || strcasecmp( avcodec_hw, "none" ) )
> -    {
> -        msg_Warn( p_dec, "threaded frame decoding is not compatible with DXVA2, disabled" );
> -        p_context->thread_type &= ~FF_THREAD_FRAME;
> -    }
> -    free( avcodec_hw );
> -# endif
> -
>      if( p_context->thread_type & FF_THREAD_FRAME )
>          p_dec->i_extra_picture_buffers = 2 * p_context->thread_count;
>  #endif
> @@ -1313,7 +1302,28 @@ static enum PixelFormat ffmpeg_GetFormat( AVCodecContext *p_context,
>      vlc_va_t *p_va = p_sys->p_va;
>
>      if( p_va != NULL )
> +    {
> +        for( size_t i = 0; pi_fmt[i] != PIX_FMT_NONE; i++ )
> +        {
> +            if( p_va->pix_fmt != pi_fmt[i] )
> +                continue;
> +
> +            if( p_context->width <= 0 || p_context->height <= 0
> +             || vlc_va_Setup( p_va, p_context, &p_dec->fmt_out.video.i_chroma ) )
> +            {
> +                msg_Err( p_dec, "reusing acceleration failed" );
> +                break;
> +            }
> +
> +            if( p_va->description )
> +                msg_Info( p_dec, "Reusing %s for hardware decoding.",
> +                          p_va->description );
> +
> +            return pi_fmt[i];
> +        }
> +
>          vlc_va_Delete( p_va, p_context );
> +    }
>
>      /* Enumerate available formats */
>      bool can_hwaccel = false;
> --
> 2.3.2
>
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