[FFmpeg-devel] [PATCH] AVHWAccel infrastructure v2 (take 6) [ping^3]

Michael Niedermayer michaelni
Wed Nov 10 13:48:38 CET 2010


On Wed, Nov 10, 2010 at 11:01:11AM +0100, Gwenole Beauchesne wrote:
> Hi,
>
> On Tue, 9 Nov 2010, Michael Niedermayer wrote:
>
>> On Tue, Nov 02, 2010 at 11:05:35AM +0100, Gwenole Beauchesne wrote:
>>>
>>> On Sat, 30 Oct 2010, Michael Niedermayer wrote:
>>>
>>>>> On Mon, 20 Sep 2010, Gwenole Beauchesne wrote:
>>>>>
>>>>>>>> So, HW accelerator selection works as is:
>>>>>>>> - Set AVCodecContext.hwaccel_id to the desired accelerator
>>>>>>>> - Set AVCodecContext.hwaccel_flags to HWACCEL_CAP_GET_PIXELS if the user
>>>>>>>> wants AVFrame.data[0-2] populated with YV12 or NV12 pixels
>>>>>>>>
>>>>>>>> This means we can handle multiple accelerators automatically at once.
>>>>>>>> Anyway, this lived in an ideal world without practical use since the
>>>>>>>> user-application would still have to handle the HW accelerator
>>>>>>>> specifically.
>>>>>>>
>>>>>>> [...]
>>>>>>>> +    /**
>>>>>>>> +     * Called in codec initialization.
>>>>>>>> +     *
>>>>>>>> +     * This is used to initialize the AVCodecContext.hwaccel_context
>>>>>>>> +     * hardware accelerator context.
>>>>>>>> +     *
>>>>>>>> +     * @param avctx the codec context
>>>>>>>> +     * @return zero if successful, a negative value otherwise
>>>>>>>> +     */
>>>>>>>> +    int (*init)(AVCodecContext *avctx);
>>>>>>>> +
>>>>>>>> +    /**
>>>>>>>> +     * Called in codec finalization.
>>>>>>>> +     *
>>>>>>>> +     * This is used to clean-up any data from the hardware accelerator
>>>>>>>> +     * context. Should this function be implemented, it shall reset
>>>>>>>> +     * AVCodecContext.hwaccel_context to NULL.
>>>>>>>> +     *
>>>>>>>> +     * @param avctx the codec context
>>>>>>>> +     * @return zero if successful, a negative value otherwise
>>>>>>>> +     */
>>>>>>>> +    int (*close)(AVCodecContext *avctx);
>>>>>>>> +
>>>>>>>> +    /**
>>>>>>>> +     * Called at the beginning of each frame to allocate a HW surface.
>>>>>>>> +     *
>>>>>>>> +     * The returned surface will be stored in Picture.data[3].
>>>>>>>> +     *
>>>>>>>> +     * @param avctx the codec context
>>>>>>>> +     * @param surface the pointer to the HW accelerator surface
>>>>>>>> +     * @return zero if successful, a negative value otherwise
>>>>>>>> +     */
>>>>>>>> +    int (*alloc_surface)(AVCodecContext *avctx, uint8_t **surface);
>>>>>>>> +
>>>>>>>> +    /**
>>>>>>>> +     * Called to free the HW surface that was allocated with
>>>>>>>> alloc_surface().
>>>>>>>> +     *
>>>>>>>> +     * @param avctx the codec context
>>>>>>>> +     * @param surface the HW accelerator surface
>>>>>>>> +     * @return zero if successful, a negative value otherwise
>>>>>>>> +     */
>>>>>>>> +    void (*free_surface)(AVCodecContext *avctx, uint8_t *surface);
>>>>>>>>  } AVHWAccel;
>>>>>>>
>>>>>>> iam not in favor of these. What are these good for?
>>>>>>> Why are they needed?
>>>>>>
>>>>>> This is used to allocate the HW surfaces (VdpSurface, VASurface, etc.)
>>>>>> from within FFmpeg. i.e. the AVFrame.data[3] part, hence the uint8_t *
>>>>>> instead of the void *.
>>>>>
>>>>> Those functions are also used to help user implement
>>>>> AVCodecContext.get_buffer() and release_buffer() if he wants to do so
>>>>> manually.
>>>>>
>>>>> e.g. by default, AVCodecContext.get_buffer() will point to
>>>>> avcodec_default_get_buffer(). If a user overrides that function, he will
>>>>> lose automatic data[3] handling. So, two possible cases:
>>>>> 1) He really knows how to do so, so he allocates the HW surface himself
>>>>> 2) He can delegate that to FFmpeg that will know how to do that just fine
>>>>> too. e.g. calling the right vaCreateSurfaces(), VdpVideoSurfaceCreate(),
>>>>> etc.
>>>>>
>>>>>>>> +/** Identifies the hardware accelerator */
>>>>>>>> +enum HWAccelID {
>>>>>>>> +    HWACCEL_ID_NONE,
>>>>>>>> +    HWACCEL_ID_VAAPI,           ///< Video Acceleration (VA) API
>>>>>>>> +    HWACCEL_ID_NB
>>>>>>>> +};
>>>>>>>
>>>>>>> this needs a any or auto for autodetection (which should be 0)
>>>>>>
>>>>>> I finally forgot about autodetection because it's too complex to handle
>>>>>> at the FFmpeg level and delegated that to the player level. In
>>>>>> particular, HWAccel context may depend on upper level info, like an X
>>>>>> display...
>>>>>>
>>>>>>>> +
>>>>>>>> +/** Identifies the hardware accelerator entry-point */
>>>>>>>> +enum HWAccelEntrypoint {
>>>>>>>> +    HWACCEL_ENTRYPOINT_VLD = 1, ///< Variable-length decoding
>>>>>>>> +    HWACCEL_ENTRYPOINT_IDCT,    ///< Inverse discrete cosine transform
>>>>>>>> +    HWACCEL_ENTRYPOINT_MOCO,    ///< Motion compensation
>>>>>>>> +    HWACCEL_ENTRYPOINT_NB
>>>>>>>> +};
>>>>>>>
>>>>>>> as said previously this is ambigous
>>>>>>>
>>>>>>> HWACCEL_ENTRYPOINT_VLD could mean the hw does just VLD and leaves IDCT/MC
>>>>>>> to software
>>>>>>
>>>>>> Actually, I didn't find the exact meaning. But from a pipeline point of
>>>>>> view, this would mean XXX and above. i.e. VLD and above, motion
>>>>>> compensation and above. Flagging those would lead to more player work
>>>>>> (well, just OR'ing more flags).
>>>>>>
>>>>>> I tried to express that in the comment.
>>>>
>>>>>  Makefile    |    2 -
>>>>>  avcodec.h   |   87 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>>>>>  hwaccel.h   |   55 +++++++++++++++++++++++++++++++++++++
>>>>>  internal.h  |   14 +++++++++
>>>>>  mpegvideo.c |    4 ++
>>>>>  options.c   |    2 +
>>>>>  utils.c     |   52 +++++++++++++++++++++++++++++++++++
>>>>>  7 files changed, 213 insertions(+), 3 deletions(-)
>>>>> e890e0f1046043c9a28d3a64d9380146b0316139  ffmpeg.hwaccel.v2.8.patch
>>>>> commit 8277742b00c2dbe41fd3af7f25c1c903f4477b43
>>>>> Author: Gwenole Beauchesne <gbeauchesne at splitted-desktop.com>
>>>>> Date:   Fri Oct 29 06:16:55 2010 +0200
>>>>>
>>>>>     Update AVHWAccel infrastructure to v2.
>>>>>
>>>>> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
>>>>> index 385ae02..1b64768 100644
>>>>> --- a/libavcodec/Makefile
>>>>> +++ b/libavcodec/Makefile
>>>>> @@ -3,7 +3,7 @@ include $(SUBDIR)../config.mak
>>>>>  NAME = avcodec
>>>>>  FFLIBS = avutil avcore
>>>>>
>>>>> -HEADERS = avcodec.h avfft.h dxva2.h opt.h vaapi.h vdpau.h xvmc.h
>>>>> +HEADERS = avcodec.h avfft.h dxva2.h hwaccel.h opt.h vaapi.h vdpau.h xvmc.h
>>>>>
>>>>>  OBJS = allcodecs.o                                                      \
>>>>>         audioconvert.o                                                   \
>>>>> diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
>>>>> index 705259e..137f485 100644
>>>>> --- a/libavcodec/avcodec.h
>>>>> +++ b/libavcodec/avcodec.h
>>>>> @@ -29,6 +29,7 @@
>>>>>  #include <errno.h>
>>>>>  #include "libavutil/avutil.h"
>>>>>  #include "libavutil/cpu.h"
>>>>> +#include "libavcodec/hwaccel.h"
>>>>>
>>>>>  #define LIBAVCODEC_VERSION_MAJOR 52
>>>>>  #define LIBAVCODEC_VERSION_MINOR 93
>>>>> @@ -2607,7 +2608,7 @@ typedef struct AVCodecContext {
>>>>>       * provided by the user. In that case, this holds display-dependent
>>>>>       * data FFmpeg cannot instantiate itself. Please refer to the
>>>>>       * FFmpeg HW accelerator documentation to know how to fill this
>>>>> -     * is. e.g. for VA API, this is a struct vaapi_context.
>>>>> +     * is. e.g. for VA API, this is a VADisplay.
>>>>>       * - encoding: unused
>>>>>       * - decoding: Set by user
>>>>>       */
>>>>
>>>>> @@ -2753,6 +2754,27 @@ typedef struct AVCodecContext {
>>>>>       * - decoding: unused
>>>>>       */
>>>>>      int slices;
>>>>> +
>>>>> +    /**
>>>>> +     * User-requested hardware accelerator. See HWACCEL_ID_xxx.
>>>>> +     * - encoding: unused
>>>>> +     * - decoding: Set by user
>>>>> +     */
>>>>> +    enum HWAccelID hwaccel_id;
>>>>
>>>> could you remind me why this is needed compared to the apparently more flexible
>>>> system with pixel formats?
>>>
>>> Before hwaccel v1, we had: PIX_FMT_<hwaccel>_<codec>. One <hwaccel> could
>>> easily have ~5 codecs. If you have 2 <haccel>, you get 10 pixel formats.
>>> Besides, you can have <codec> supported at different entrypoint. e.g.
>>> VLD, MoComp, IDCT. Thus, we could have combinatorial explosion.
>>>
>>> With hwaccel v1, we factored this with PIX_FMT_<hwaccel>_<entrypoint>,
>>> the <codec> information became irrelevant. <entrypoint> was reduced to
>>> typically 1 to 3. What does a pixel format with a <codec> name in it
>>> actually mean anyway?
>>>
>>> This is better, but this was still silly. A pixel format defines... well,
>>> a pixel format. If the user wants to extract the decoded pixels from the
>>> GPU, he requires so with AV_HWACCEL_CAP_GET_PIXELS. The pixel format of
>>> those needs to be expressed the usual way, e.g. avctx->pix_fmt ==
>>> PIX_FMT_YUV420P. How would this have been expressed if avctx->pix_fmt was
>>> PIX_FMT_<hwaccel>_<entrypoint>?
>>
>> "A pixel format defines... well, a pixel format."
>> thats a useless circular definition
>>
>> a pixel format defines the structuring of data in AVFrame.data[]
>> that likely differs between 2 hw accelerator APIs, so should allow selecting
>> hw accelerators
>
> And how do you define and select an HW accelerator that outputs NV12 or  
> I420 frames? Or other HW accelerators that the user requested decoded  
> pixels back to .data[0-2]?

easy, pix_fmt = PIX_FMT_NV12
its fully transparent then the user app does not even need to know a hwaccel
is used


>
> Would you introduce another level with the actual pixel format. e.g.  
> PIX_FMT_YUV420P_<hwaccel>_<entrypoint>?
>
>>> Besides, from an implementation point of view (in libavcodec), the pre-v1
>>> and v1 way of using pixel formats becomes tedious to handle.
>>>
>>> We currently have hooks called through:
>>>
>>> if (avctx->hwaccel)
>>>   avctx->hwaccel->decode_slice(...);
>>>
>>> this needs to become:
>>> if (avctx->hwaccel && <is entrypoint VLD>)
>>>   avctx->hwaccel->decode_slice(...);
>>>
>>> so that other entry-points could be managed easily.
>>>
>>> With the v1 way, <is entrypoint == VLD> becomes a big evil switch:
>>> return avctx->pix_fmt == PIX_FMT_hwaccel1_VLD ||?avctx->pix_fmt ==
>>> PIX_FMT_hwaccel2_VLD || avcxtx->pix_fmt == PIX_FMT_hwaccel3_VLD, etc.
>>>
>>> Horrible, isn't it?
>>
>> pix_fmt_descriptor[pix_fmt].flags & FLAG_VLD
>> doesnt look horrible to me
>
> if (avctx->hwaccel && avctx->hwaccel->entrypoint == HWACCEL_ENTRYPOINT_VLD)
> looks better, less indirections, and keeps things on a single line. :)

if you put entrypoint in hwaccel you need a seperate
AVHWAccel for each entrypoint. and then you could just do
if(avctx->hwaccel && avctx->hwaccel->decode_slice)

    
[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The greatest way to live with honor in this world is to be what we pretend
to be. -- Socrates
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