[FFmpeg-devel] [PATCH] libavcodec/vp9: Fix VP9 dynamic resolution changing decoding on VAAPI.

[Yan Wang]

On 5/28/2019 4:43 PM, Hendrik Leppkes wrote:
> On Tue, May 28, 2019 at 9:46 AM Yan Wang <yan.wang at linux.intel.com> wrote:
>>
>> On 5/28/2019 3:16 PM, Hendrik Leppkes wrote:
>>> On Tue, May 28, 2019 at 8:57 AM Yan Wang <yan.wang at linux.intel.com> wrote:
>>>> When the format change, the VAAPI context cannot be destroyed.
>>>> Otherwise, the reference frame surface will lost.
>>>>
>>>> Signed-off-by: Yan Wang <yan.wang at linux.intel.com>
>>>> ---
>>>>    libavcodec/decode.c | 6 ++++++
>>>>    1 file changed, 6 insertions(+)
>>>>
>>>> diff --git a/libavcodec/decode.c b/libavcodec/decode.c
>>>> index 6c31166ec2..3eda1dc42c 100644
>>>> --- a/libavcodec/decode.c
>>>> +++ b/libavcodec/decode.c
>>>> @@ -1397,7 +1397,9 @@ int ff_get_format(AVCodecContext *avctx, const enum AVPixelFormat *fmt)
>>>>
>>>>        for (;;) {
>>>>            // Remove the previous hwaccel, if there was one.
>>>> +#if !CONFIG_VP9_VAAPI_HWACCEL
>>>>            hwaccel_uninit(avctx);
>>>> +#endif
>>>>
>>>>            user_choice = avctx->get_format(avctx, choices);
>>>>            if (user_choice == AV_PIX_FMT_NONE) {
>>>> @@ -1479,7 +1481,11 @@ int ff_get_format(AVCodecContext *avctx, const enum AVPixelFormat *fmt)
>>>>                       "missing configuration.\n", desc->name);
>>>>                goto try_again;
>>>>            }
>>>> +#if CONFIG_VP9_VAAPI_HWACCEL
>>>> +        if (hw_config->hwaccel && !avctx->hwaccel) {
>>>> +#else
>>>>            if (hw_config->hwaccel) {
>>>> +#endif
>>>>                av_log(avctx, AV_LOG_DEBUG, "Format %s requires hwaccel "
>>>>                       "initialisation.\n", desc->name);
>>>>                err = hwaccel_init(avctx, hw_config);
>>>> --
>>>> 2.17.2
>>>>
>>> This change feels just wrong. First of all, preprocessors are
>>> absolutely the wrong way to go about this.
>> Sorry for this. I am new guy for ffmpeg development. What way should be
>>
>> better? I can refine it.
>>
>>> Secondly, if the frames need to change size, or surface format, then
>>> this absolutely needs to be called, doesn't it?
>> Based on VP9 spec, the frame resolution can be changed per frame. But
>> current
>>
>> frame will need refer to previous frame still. So if destroy the VAAPI
>> context, it
>>
>> will cause reference frame surface in VAAPI driver lost.
>>
>> In fact, this patch is for the issue:
>>
>> https://github.com/intel/media-driver/issues/629
>>
>> its 2nd frame (128x128) will refer to the 1st frame (256x256).
>>
> This may work if the frame size decreases, but what if it increases?
> Then the frame buffers in the pool are too small, and anything could
> go wrong.
> This won't be an easy issue to solve, and needs very careful design.

Agree. I should add [RFC] for this patch.

I can investigate frame buffer management of ffmpeg and submit new patch 
for covering this situation.

Thanks for comments.

Yan Wang

>
> - Hendrik
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