[FFmpeg-devel] [PATCH] HW accelerator: Indicate when HW acceleration is in use

[Lim, Michele]

Mark, 

Thanks for your response.  I agree with you and actually had an implementation similar to what you've described for the decoder but abandoned it; I haven't found an elegant way without making too many changes to indicate it much later when hardware is actually set up for execution.  This is being handled in a loop for all possible pixel formats supported by the display surface. (for my display there are 9, so the same message is logged 9 times).

A more elegant solution will require additional code which is against FFmpeg guideline.  I think this benefits everyone wanting assurance as to whether the coding or decoding is done using the hardware or software path.

Meanwhile, I can submit with the not-so-elegant solution so that you can see what I mean - this is just for the decoder.

I will look into adding more code for a more elegant solution, if that's acceptable.  Please let me know which way is best.

Thanks,
Michele

-----Original Message-----
From: ffmpeg-devel [mailto:ffmpeg-devel-bounces at ffmpeg.org] On Behalf Of Mark Thompson
Sent: Saturday, November 4, 2017 12:09 PM
To: ffmpeg-devel at ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH] HW accelerator: Indicate when HW acceleration is in use

On 03/11/17 18:35, Michele Lim wrote:
> Having clear indication of when a hardware accelerator is in operation 
> prevents false assumptions, for e.g., in situations when the command 
> line argument inadvertently omits options for enabling it, resulting 
> to the framework silently switching to the SW path.
> 
> Signed-off-by: Michele Lim <michele.lim at intel.com>
> ---
>  fftools/ffmpeg_hw.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/fftools/ffmpeg_hw.c b/fftools/ffmpeg_hw.c index 
> a4d1cad..f071746 100644
> --- a/fftools/ffmpeg_hw.c
> +++ b/fftools/ffmpeg_hw.c
> @@ -306,6 +306,8 @@ int hw_device_setup_for_decode(InputStream *ist)
>      if (!ist->dec_ctx->hw_device_ctx)
>          return AVERROR(ENOMEM);
>  
> +    /* Indicate HW accelerator has been prepared for decode */
> +    av_log(ist->dec_ctx, AV_LOG_INFO, "HW accelerator prepared for 
> + decode: %s\n", av_hwdevice_get_type_name(type));
>      return 0;
>  }
>  
> @@ -331,6 +333,9 @@ int hw_device_setup_for_encode(OutputStream *ost)
>          // No device required.
>          return 0;
>      }
> +
> +    /* Indicate HW accelerator has been prepared for encode */
> +    av_log(ost->enc_ctx, AV_LOG_INFO, "HW accelerator prepared for 
> + encode: %s\n", av_hwdevice_get_type_name(type));
>  }
>  
>  static int hwaccel_retrieve_data(AVCodecContext *avctx, AVFrame 
> *input)
> 

I don't think this does what you want.  It is only a preparation step which sets hardware devices which might then be used by a codec, and tells you little about whether it is actually used in practice.  Consider that your message will appear when setting -hwaccel_device and decoding with a random codec with no hardware support, and also when a codec does support some hardware but not the actual stream being decoded (e.g. H.264 4:2:2).

If you want a message like this (which I admit ambivalence to, but if other people think it's useful then sure), I think it has to be logged later when we actually know whether the hardware is usable - either inside lavc or in ffmpeg.c after a frame is returned.

- Mark
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