On 06/09/17 17:29, wm4 wrote:
> On Wed, 6 Sep 2017 16:53:04 +0100
> Mark Thompson <[email protected]> wrote:
> 
>> On 06/09/17 15:37, wm4 wrote:
>>> On Tue,  5 Sep 2017 23:59:31 +0100
>>> Mark Thompson <[email protected]> wrote:
>>>   
>>>> ---
>>>>  doc/APIchanges       |  3 +++
>>>>  libavcodec/avcodec.h | 23 +++++++++++++++++++++++
>>>>  2 files changed, 26 insertions(+)
>>>>
>>>> diff --git a/doc/APIchanges b/doc/APIchanges
>>>> index 6f70f3c96..f21dc4db0 100644
>>>> --- a/doc/APIchanges
>>>> +++ b/doc/APIchanges
>>>> @@ -14,6 +14,9 @@ libavutil:     2017-03-23
>>>>  API changes, most recent first:
>>>>  
>>>>  2017-xx-xx - xxxxxxx - lavc 58.x+1.0 - avcodec.h
>>>> +  Add AVCodecHWConfig and AVCodec.hw_configs.
>>>> +
>>>> +2017-xx-xx - xxxxxxx - lavc 58.x+1.0 - avcodec.h
>>>>    Add AV_HWACCEL_FLAG_REUSE_CONTEXT.
>>>>  
>>>>  2017-xx-xx - xxxxxxx - lavfi 7.x+1.0 - avfilter.h
>>>> diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
>>>> index 89e432d16..4f6b76203 100644
>>>> --- a/libavcodec/avcodec.h
>>>> +++ b/libavcodec/avcodec.h
>>>> @@ -35,6 +35,7 @@
>>>>  #include "libavutil/cpu.h"
>>>>  #include "libavutil/dict.h"
>>>>  #include "libavutil/frame.h"
>>>> +#include "libavutil/hwcontext.h"
>>>>  #include "libavutil/log.h"
>>>>  #include "libavutil/pixfmt.h"
>>>>  #include "libavutil/rational.h"
>>>> @@ -2773,6 +2774,19 @@ typedef struct AVProfile {
>>>>      const char *name; ///< short name for the profile
>>>>  } AVProfile;
>>>>  
>>>> +typedef struct AVCodecHWConfig {
>>>> +    /**
>>>> +     * A device type which can be supplied to the codec.
>>>> +     */
>>>> +    enum AVHWDeviceType device_type;
>>>> +    /**
>>>> +     * The matching hardware pixel format which the codec can produce.
>>>> +     *
>>>> +     * Set to AV_PIX_FMT_NONE if no hardware pixel format is available.
>>>> +     */
>>>> +    enum AVPixelFormat pix_fmt;
>>>> +} AVCodecHWConfig;
>>>> +
>>>>  typedef struct AVCodecDefault AVCodecDefault;
>>>>  
>>>>  struct AVSubtitle;
>>>> @@ -2808,6 +2822,15 @@ typedef struct AVCodec {
>>>>      const AVClass *priv_class;              ///< AVClass for the private 
>>>> context
>>>>      const AVProfile *profiles;              ///< array of recognized 
>>>> profiles, or NULL if unknown, array is terminated by {FF_PROFILE_UNKNOWN}
>>>>  
>>>> +    /**
>>>> +     * Array of hardware configurations supported by the codec, or NULL
>>>> +     * if no hardware supported.
>>>> +     *
>>>> +     * The array is terminated by a configuration with a device_type of
>>>> +     * AV_HW_DEVICE_TYPE_NONE.
>>>> +     */
>>>> +    const AVCodecHWConfig *hw_configs;
>>>> +
>>>>      /*****************************************************************
>>>>       * No fields below this line are part of the public API. They
>>>>       * may not be used outside of libavcodec and can be changed and  
>>>
>>> What if a decoder provides hardware decoding, but has no associated
>>> AVHWDeviceType? (Such as mmal.)  
>>
>> They are in the pix_fmts list.  What other information do you want?
> 
> They don't necessarily output a hw format. For example, crystalhd
> (ffmpeg only) doesn't. It would also not be very uniform.

If it doesn't require any additional setup and it outputs software frames then 
it's indistinguishable from a normal software decoder; therefore, treat it as 
such.

MMAL is harder - I'm only treating the real hwaccels here because they now have 
a consistent form we can make use of.

I haven't really thought about this properly, but how about something like:

enum AVCodecHWConfigMethod {
  AV_CODEC_HW_CONFIG_METHOD_HW_DEVICE = 1,
  AV_CODEC_HW_CONFIG_METHOD_HW_FRAMES = 2,
  AV_CODEC_HW_CONFIG_METHOD_LEGACY_SHIT = 4,
  AV_CODEC_HW_CONFIG_METHOD_MAGIC = 8,
};

struct AVCodecHWConfig {
  int methods;
  enum AVHWDeviceType device_type;
  enum AVPixelFormat pix_fmt;
};

Then you would label MMAL as MAGIC, because it can just output the MMAL frames 
without additional setup.  VAAPI/VDPAU would be HW_DEVICE | HW_FRAMES | 
LEGACY_SHIT.  QSV would be HW_FRAMES | LEGACY_SHIT.

Is there then sufficient information for ff_get_format() to look at this list 
to decide on whether it needs an AVHWAccel, and therefore eliminate dummy 
hwaccels?

- Mark
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