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

Gwenole Beauchesne gbeauchesne
Wed Nov 10 11:01:11 CET 2010


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]?

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. :)



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