[FFmpeg-devel] [PATCH v3] fftools/ffmpeg: add an option to forbid the fallback to software path when hardware init fails

[Mark Thompson]

On 09/11/18 09:05, Linjie Fu wrote:
> Currently ff_get_format will go through all usable choices if the chosen
> format was not supported. It will fallback to software path if the hardware
> init fails.
> 
> Provided an option "-require_hwaccel 1" in user-code to detect frame->format and
> hwaccel_get_buffer in get_buffer. If hardware init fails, returns an error.
> 
> Signed-off-by: Linjie Fu <linjie.fu at intel.com>
> ---
> [v2] detect hardware init failures in get_buffer and modify in user-code
> [v3] changed the option name, add error message
> 
>  fftools/ffmpeg.c     | 4 ++++
>  fftools/ffmpeg.h     | 3 +++
>  fftools/ffmpeg_opt.c | 4 ++++
>  3 files changed, 11 insertions(+)
> 
> diff --git a/fftools/ffmpeg.c b/fftools/ffmpeg.c
> index da4259a9a8..113ab6312a 100644
> --- a/fftools/ffmpeg.c
> +++ b/fftools/ffmpeg.c
> @@ -2890,6 +2890,10 @@ static int get_buffer(AVCodecContext *s, AVFrame *frame, int flags)
>  
>      if (ist->hwaccel_get_buffer && frame->format == ist->hwaccel_pix_fmt)
>          return ist->hwaccel_get_buffer(s, frame, flags);
> +    else if (ist->require_hwaccel) {
> +        av_log(s, AV_LOG_ERROR, "Hardware acceleration is required and will not fallback to try software path.\n");
> +        return AVERROR(EINVAL);
> +    }

Um, doesn't this just break every hardware case except QSV?  The hwaccel_get_buffer function is only used for QSV, and will be unset for any other cases.  (In fact, I don't think it does anything useful there anyway - maybe it can be removed completely, I'll have a look.)

I think the right place to make this decision (to force a hardware format) is in get_format(), rather than after when the decoder is already configured - this avoids cases where the format you actually wanted was available but you didn't pick it and then fail later.  I had a patch lying around for another purpose which gives you some support for this, just sent if you'd like to have a look.

>  
>      return avcodec_default_get_buffer2(s, frame, flags);
>  }
> diff --git a/fftools/ffmpeg.h b/fftools/ffmpeg.h
> index eb1eaf6363..a5c85daa67 100644
> --- a/fftools/ffmpeg.h
> +++ b/fftools/ffmpeg.h
> @@ -133,6 +133,8 @@ typedef struct OptionsContext {
>      int        nb_hwaccel_output_formats;
>      SpecifierOpt *autorotate;
>      int        nb_autorotate;
> +    SpecifierOpt *require_hwaccel;
> +    int        nb_require_hwaccel;
>  
>      /* output options */
>      StreamMap *stream_maps;
> @@ -365,6 +367,7 @@ typedef struct InputStream {
>      enum AVHWDeviceType hwaccel_device_type;
>      char  *hwaccel_device;
>      enum AVPixelFormat hwaccel_output_format;
> +    int require_hwaccel;
>  
>      /* hwaccel context */
>      void  *hwaccel_ctx;
> diff --git a/fftools/ffmpeg_opt.c b/fftools/ffmpeg_opt.c
> index d4851a2cd8..6890bb7fcf 100644
> --- a/fftools/ffmpeg_opt.c
> +++ b/fftools/ffmpeg_opt.c
> @@ -730,6 +730,7 @@ static void add_input_streams(OptionsContext *o, AVFormatContext *ic)
>          ist->autorotate = 1;
>          MATCH_PER_STREAM_OPT(autorotate, i, ist->autorotate, ic, st);
>  
> +        MATCH_PER_STREAM_OPT(require_hwaccel, i, ist->require_hwaccel, ic, st);
>          MATCH_PER_STREAM_OPT(codec_tags, str, codec_tag, ic, st);
>          if (codec_tag) {
>              uint32_t tag = strtol(codec_tag, &next, 0);
> @@ -3600,6 +3601,9 @@ const OptionDef options[] = {
>      { "autorotate",       HAS_ARG | OPT_BOOL | OPT_SPEC |
>                            OPT_EXPERT | OPT_INPUT,                                { .off = OFFSET(autorotate) },
>          "automatically insert correct rotate filters" },
> +    { "require_hwaccel",  HAS_ARG | OPT_BOOL | OPT_SPEC |
> +                          OPT_EXPERT | OPT_INPUT,                                { .off = OFFSET(require_hwaccel)},
> +      "forbid the fallback to default software path when hardware init fails"},
>  
>      /* audio options */
>      { "aframes",        OPT_AUDIO | HAS_ARG  | OPT_PERFILE | OPT_OUTPUT,           { .func_arg = opt_audio_frames },
>