[FFmpeg-devel] [PATCH] libavutil/hwcontext_qsv: Command line using hwaccel 'QSV' doesn't work

Mark Thompson sw at jkqxz.net
Tue Jan 3 15:14:39 EET 2017


On 03/01/17 07:13, Huang, Zhengxu wrote:
> From 687ce9c804b2618f021100235c46a33b48fa522c Mon Sep 17 00:00:00 2001
> From: Zhengxu <zhengxu.maxwell at gmail.com>
> Date: Wed, 14 Dec 2016 11:55:31 +0800
> Subject: [PATCH] libavutil/hwcontext_qsv: Command line using hwaccel 'QSV'
>  doesn't work.
> 
> Command: ffmpeg -hwaccel qsv -c:v h264_qsv -i test.264 -c:v h264_qsv out.264
> 
> Reason: hwcontext_qsv will create a child hwcontext_vaapi. VAAPI will
>  open X11 display ":0.0" defaultly. However, MSDK doesn't support X11 so
>  far. This results in the failure of this command.
> 
> Fix: When using VAAPI, let VAAPI try to create DRM display handle by scanning
>  device nodes under '/dev/dri/'.

We already default to attempting to open the first render node inside hwcontext_vaapi (if opening via X11 fails):

http://git.videolan.org/?p=ffmpeg.git;a=blob;f=libavutil/hwcontext_vaapi.c;h=6176bdc880c81dec7cac0b214a8d55f3b1160abc;hb=HEAD#l936

I think if you want this behaviour it would be better to add code there rather than in hwcontext_qsv (which doesn't really care about this aspect at all, it just wants a usable subdevice for the platform).

Can you explain your case which hits this?  Do you have some other external graphics card(s) along with the on-chip Intel graphics?  For that case, I don't like the idea of scanning for a device node because it is perfectly possible to get a valid VADisplay handle for a non-QSV device (an AMD or Nvidia card with mesa, most obviously) which will then fail opaquely later when libmfx tries to use it because the Intel proprietary driver is required.  This may even fail randomly, because device nodes associated with independent drivers are not ordered.

> Signed-off-by: ChaoX A Liu <chaox.a.liu at gmail.com>
> Signed-off-by: Huang, Zhengxu <zhengxu.maxwell at gmail.com>
> Signed-off-by: Andrew, Zhang <huazh407 at gmail.com>
> ---
>  libavutil/hwcontext_qsv.c | 44 +++++++++++++++++++++++++++++++-------------
>  1 file changed, 31 insertions(+), 13 deletions(-)
> 
> diff --git a/libavutil/hwcontext_qsv.c b/libavutil/hwcontext_qsv.c
> index 2dc9aca..2701b5a 100644
> --- a/libavutil/hwcontext_qsv.c
> +++ b/libavutil/hwcontext_qsv.c
> @@ -707,12 +707,41 @@ static mfxIMPL choose_implementation(const char *device)
>      return impl;
>  }
>  
> +static int create_proper_child_device(AVBufferRef **ctx, const char *device, int flags)
> +{
> +    enum AVHWDeviceType child_device_type;
> +    char adapter[256];
> +    int  adapter_num;
> +
> +    if (CONFIG_VAAPI)
> +        child_device_type = AV_HWDEVICE_TYPE_VAAPI;
> +    else if (CONFIG_DXVA2)
> +        child_device_type = AV_HWDEVICE_TYPE_DXVA2;
> +    else
> +        return AVERROR(ENOSYS);
> +
> +    if (device || CONFIG_DXVA2)
> +        return av_hwdevice_ctx_create(ctx, child_device_type, device, NULL, flags);
> +
> +    for (adapter_num = 0; adapter_num < 6; adapter_num++) {
> +        if (adapter_num < 3)
> +            snprintf(adapter,sizeof(adapter),
> +                "/dev/dri/renderD%d", adapter_num+128);
> +        else
> +            snprintf(adapter,sizeof(adapter),
> +                "/dev/dri/card%d", adapter_num-3);

I would prefer not to open the DRM master device (/dev/dri/card*) by default - until very recent kernels it was exclusive-access-only, so nothing else can use the graphics at the same time (most obviously another ffmpeg instance).

> +        if (av_hwdevice_ctx_create(ctx, child_device_type, adapter, NULL, flags) == 0)
> +            return 0;
> +    }
> +
> +    return AVERROR(ENOSYS);
> +}
> +
>  static int qsv_device_create(AVHWDeviceContext *ctx, const char *device,
>                               AVDictionary *opts, int flags)
>  {
>      AVQSVDeviceContext *hwctx = ctx->hwctx;
>      QSVDevicePriv *priv;
> -    enum AVHWDeviceType child_device_type;
>      AVDictionaryEntry *e;
>  
>      mfxVersion    ver = { { 3, 1 } };
> @@ -730,18 +759,7 @@ static int qsv_device_create(AVHWDeviceContext *ctx, const char *device,
>      ctx->free        = qsv_device_free;
>  
>      e = av_dict_get(opts, "child_device", NULL, 0);
> -
> -    if (CONFIG_VAAPI)
> -        child_device_type = AV_HWDEVICE_TYPE_VAAPI;
> -    else if (CONFIG_DXVA2)
> -        child_device_type = AV_HWDEVICE_TYPE_DXVA2;
> -    else {
> -        av_log(ctx, AV_LOG_ERROR, "No supported child device type is enabled\n");
> -        return AVERROR(ENOSYS);
> -    }
> -
> -    ret = av_hwdevice_ctx_create(&priv->child_device_ctx, child_device_type,
> -                                 e ? e->value : NULL, NULL, 0);
> +    ret = create_proper_child_device(&priv->child_device_ctx, e ? e->value : NULL, 0);
>      if (ret < 0)
>          return ret;
>  
> -- 
> 1.8.3.1
> 

For your specific case in the ffmpeg utility it might be best to add a new command-line option (-qsv_device?) and then pass it as the "child_device" in the options dictionary?  I admit this isn't necessarily helpful for other users, but it would fix your command above without running into the other problems above.

Thanks,

- Mark



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