Re: [FFmpeg-devel] [PATCH v2 1/3] avcodec/snowenc: AV_CODEC_CAP_ENCODER_RECON_FRAME support

[James Almer <jamrial@gmail.com>]

On 3/23/2023 6:50 AM, Michael Niedermayer wrote:
> On Mon, Mar 20, 2023 at 07:07:59PM -0300, James Almer wrote:
>> On 3/19/2023 4:42 PM, Michael Niedermayer wrote:
>>> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
>>> ---
>>>    libavcodec/snowenc.c | 10 +++++++++-
>>>    1 file changed, 9 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/libavcodec/snowenc.c b/libavcodec/snowenc.c
>>> index 658684c575..5fb5906ed8 100644
>>> --- a/libavcodec/snowenc.c
>>> +++ b/libavcodec/snowenc.c
>>> @@ -26,6 +26,7 @@
>>>    #include "avcodec.h"
>>>    #include "codec_internal.h"
>>>    #include "encode.h"
>>> +#include "internal.h" //For AVCodecInternal.recon_frame
>>>    #include "me_cmp.h"
>>>    #include "packet_internal.h"
>>>    #include "snow_dwt.h"
>>> @@ -1576,6 +1577,7 @@ static int encode_frame(AVCodecContext *avctx, AVPacket *pkt,
>>>    {
>>>        SnowContext *s = avctx->priv_data;
>>>        RangeCoder * const c= &s->c;
>>> +    AVCodecInternal *avci = avctx->internal;
>>>        AVFrame *pic;
>>>        const int width= s->avctx->width;
>>>        const int height= s->avctx->height;
>>> @@ -1877,6 +1879,10 @@ redo_frame:
>>>                                       s->encoding_error,
>>>                                       (s->avctx->flags&AV_CODEC_FLAG_PSNR) ? SNOW_MAX_PLANES : 0,
>>>                                       s->current_picture->pict_type);
>>> +    if (s->avctx->flags & AV_CODEC_FLAG_RECON_FRAME) {
>>> +        av_frame_unref(avci->recon_frame);
>>> +        av_frame_ref(avci->recon_frame, s->current_picture);
>>> +    }
>>>        pkt->size = ff_rac_terminate(c, 0);
>>>        if (s->current_picture->key_frame)
>>> @@ -1934,7 +1940,9 @@ const FFCodec ff_snow_encoder = {
>>>        CODEC_LONG_NAME("Snow"),
>>>        .p.type         = AVMEDIA_TYPE_VIDEO,
>>>        .p.id           = AV_CODEC_ID_SNOW,
>>> -    .p.capabilities = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_ENCODER_REORDERED_OPAQUE,
>>> +    .p.capabilities = AV_CODEC_CAP_DR1 |
>>> +                      AV_CODEC_CAP_ENCODER_REORDERED_OPAQUE |
>>> +                      AV_CODEC_CAP_ENCODER_RECON_FRAME,
>>>        .priv_data_size = sizeof(SnowContext),
>>>        .init           = encode_init,
>>>        FF_CODEC_ENCODE_CB(encode_frame),
>>
>> Testing with the tool from https://git.khirnov.net/libav.git/commit/?h=recon&id=d78e17840347abfe10b2bc7e789c60665de56e1f
>> (Which i hope will be upstreamed eventually) i get
>>
>> $ tools/enc_recon_frame_test input.y4m snow flags=+bitexact 10
>> Checksum mismatch in frame ts=0, plane 0
> 
> I cannot replicate this, using matrixbench and above command line i get no
> mismatches, where can i find the input.y4m you used ?

It was https://0x0.st/sfRh.y4m

> 
> also would be nice if this tool would write a image showing the difference
> 
> thx
> 
>>
>> I don't know if this really matters for snow (is it mean to be bitexact?),
>> but it seems the very first frame returned by the reconstructed frame API is
>> not the same as the one output by the snow decoder. The rest seem to match,
>> though.
> 
> This sounds rather strange, the first frame would be used as reference for
> motion compensation so the subsequent frames matching after a mismatch is
> "surprising"

I tried other supported encoders like libx264 and librav1e and none of 
them report mismatches.

> 
> thx
> 
> [...]
> 
> 
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