Re: [FFmpeg-devel] [PATCH v2 1/3] avutil/hwcontext: add a function to get the AVHWDeviceType

["Wu, Tong1" <tong1.wu-at-intel.com@ffmpeg.org>]

> > > On Jun 30, 2022, at 7:56 PM, Andreas Rheinhardt
> > <andreas.rheinhardt@outlook.com> wrote:
> > >
> > > "zhilizhao(赵志立)":
> > >>
> > >>
> > >>> On Jun 30, 2022, at 4:43 PM, Anton Khirnov <anton@khirnov.net>
> wrote:
> > >>>
> > >>> Quoting Tong Wu (2022-06-30 04:45:56)
> > >>>> Add a function to get the corresponding AVHWDeviceType from a
> > >>>> given hardware pixel format.
> > >>>>
> > >>>> Signed-off-by: Tong Wu <tong1.wu@intel.com>
> > >>>> ---
> > >>>> libavutil/hwcontext.c | 12 ++++++++++++ libavutil/hwcontext.h |
> > >>>> 9
> > >>>> +++++++++
> > >>>> 2 files changed, 21 insertions(+)
> > >>>>
> > >>>> diff --git a/libavutil/hwcontext.c b/libavutil/hwcontext.c index
> > >>>> ab9ad3703e..3521ed34f4 100644
> > >>>> --- a/libavutil/hwcontext.c
> > >>>> +++ b/libavutil/hwcontext.c
> > >>>> @@ -80,6 +80,18 @@ static const char *const hw_type_names[] = {
> > >>>>    [AV_HWDEVICE_TYPE_VULKAN] = "vulkan", };
> > >>>>
> > >>>> +enum AVHWDeviceType av_hwdevice_get_type_by_pix_fmt(enum
> > >>>> +AVPixelFormat fmt) {
> > >>>> +    int i, j;
> > >>>
> > >>> Nit: you can and should declare loop indices in the loop statement
> > >>> itself
> 
> Sure, will modify them in v3.
> 
> > >>>
> > >>>> +    for (i = 0; hw_table[i]; i++) {
> > >>>> +        for (j = 0; hw_table[i]->pix_fmts[j] != AV_PIX_FMT_NONE; j++) {
> > >>>> +            if (hw_table[i]->pix_fmts[j] == fmt)
> > >>>> +                return hw_table[i]->type;
> > >>>> +        }
> > >>>> +    }
> > >>>> +    return AV_HWDEVICE_TYPE_NONE; }
> > >>>> +
> > >>>> enum AVHWDeviceType av_hwdevice_find_type_by_name(const char
> > *name)
> > >>>> {
> > >>>>    int type;
> > >>>> diff --git a/libavutil/hwcontext.h b/libavutil/hwcontext.h index
> > >>>> c18b7e1e8b..97f94403e2 100644
> > >>>> --- a/libavutil/hwcontext.h
> > >>>> +++ b/libavutil/hwcontext.h
> > >>>> @@ -229,6 +229,15 @@ typedef struct AVHWFramesContext {
> > >>>>    int width, height;
> > >>>> } AVHWFramesContext;
> > >>>>
> > >>>> +/**
> > >>>> + * Get the device type by a given pixel format.
> > >>>> + *
> > >>>> + * @param fmt Pixel format from enum AVPixelFormat.
> > >>>> + * @return The type from enum AVHWDeviceType, or
> > AV_HWDEVICE_TYPE_NONE if
> > >>>> + *         not found.
> > >>>> + */
> > >>>> +enum AVHWDeviceType av_hwdevice_get_type_by_pix_fmt(enum
> > >>>> +AVPixelFormat fmt);
> > >>>
> > >>> I wonder if we should consider the possibility of a format being
> > >>> supported by more than one device type.
> > >>
> > >> For future proof, we can make it clear that there is no guarantee
> > >> that the device type is unique, e.g.,
> > >>
> > >> "Get any device type which support the given pixel format”
> > >>
> > >
> > > Then you'd need to return a list or modify the user accept an iterator.
> >
> > Iterator should be fine.
> >
> > However, the use case is unclear: since we only return an
> > AVHWDeviceType without description like av_pix_fmt_desc_get(), user
> > has little information to skip to the next one, unless user only wants
> > to get all of the device types which support a pixel format.
> 
> Since so far there's no hardware format being supported by more than one
> hardware device, can we just keep current implementation and clarify it in
> comments such as "Get any device type which support the given pixel
> format”?
> 
> Thanks,
> Tong
> 

Plus, do you think adding a AV_PIX_FMT_FLAG_HWACCEL check for the input pixel format and change the function name to av_hwdevice_get_type_by_hwaccel_pix_fmt will help? Let users know only hardware pixel formats are acceptable for this function and like I said at this moment not any hardware format is supported by more than one hardware devices.

Tong

> >
> > >
> > > - Andreas
> > > _______________________________________________
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