Re: [FFmpeg-devel] [PATCH 11/13] ffv1dec: reference the current packet into the main context

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Lynne:
> On 10/03/2025 18:42, Lynne wrote:
>> On 10/03/2025 04:14, Andreas Rheinhardt wrote:
>>> Lynne:
>>>> ---
>>>>   libavcodec/ffv1.h    |  3 +++
>>>>   libavcodec/ffv1dec.c | 19 +++++++++++++++++--
>>>>   2 files changed, 20 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/libavcodec/ffv1.h b/libavcodec/ffv1.h
>>>> index 8c0e71284d..860a5c14b1 100644
>>>> --- a/libavcodec/ffv1.h
>>>> +++ b/libavcodec/ffv1.h
>>>> @@ -174,6 +174,9 @@ typedef struct FFV1Context {
>>>>        * NOT shared between frame threads.
>>>>        */
>>>>       uint8_t           frame_damaged;
>>>> +
>>>> +    /* Reference to the current packet */
>>>> +    AVPacket *pkt_ref;
>>>>   } FFV1Context;
>>>>   int ff_ffv1_common_init(AVCodecContext *avctx, FFV1Context *s);
>>>> diff --git a/libavcodec/ffv1dec.c b/libavcodec/ffv1dec.c
>>>> index eaa21eebdf..6396f22f79 100644
>>>> --- a/libavcodec/ffv1dec.c
>>>> +++ b/libavcodec/ffv1dec.c
>>>> @@ -469,6 +469,10 @@ static av_cold int decode_init(AVCodecContext
>>>> *avctx)
>>>>       f->pix_fmt = AV_PIX_FMT_NONE;
>>>>       f->configured_pix_fmt = AV_PIX_FMT_NONE;
>>>> +    f->pkt_ref = av_packet_alloc();
>>>> +    if (!f->pkt_ref)
>>>> +        return AVERROR(ENOMEM);
>>>> +
>>>>       if ((ret = ff_ffv1_common_init(avctx, f)) < 0)
>>>>           return ret;
>>>> @@ -701,6 +705,10 @@ static int decode_frame(AVCodecContext *avctx,
>>>> AVFrame *rframe,
>>>>       /* Start */
>>>>       if (hwaccel) {
>>>> +        ret = av_packet_ref(f->pkt_ref, avpkt);
>>>> +        if (ret < 0)
>>>> +            return ret;
>>>> +
>>>>           ret = hwaccel->start_frame(avctx, avpkt->data, avpkt->size);
>>>>           if (ret < 0)
>>>>               return ret;
>>>> @@ -720,15 +728,21 @@ static int decode_frame(AVCodecContext *avctx,
>>>> AVFrame *rframe,
>>>>               uint32_t len;
>>>>               ret = find_next_slice(avctx, avpkt->data, buf_end, i,
>>>>                                     &pos, &len);
>>>> -            if (ret < 0)
>>>> +            if (ret < 0) {
>>>> +                av_packet_unref(f->pkt_ref);
>>>>                   return ret;
>>>> +            }
>>>>               buf_end -= len;
>>>>               ret = hwaccel->decode_slice(avctx, pos, len);
>>>> -            if (ret < 0)
>>>> +            if (ret < 0) {
>>>> +                av_packet_unref(f->pkt_ref);
>>>>                   return ret;
>>>> +            }
>>>>           }
>>>> +
>>>> +        av_packet_unref(f->pkt_ref);
>>>>       } else {
>>>>           ret = decode_slices(avctx, c, avpkt);
>>>>           if (ret < 0)
>>>> @@ -827,6 +841,7 @@ static av_cold int
>>>> ffv1_decode_close(AVCodecContext *avctx)
>>>>       ff_progress_frame_unref(&s->last_picture);
>>>>       av_refstruct_unref(&s->hwaccel_last_picture_private);
>>>> +    av_packet_free(&s->pkt_ref);
>>>>       ff_ffv1_close(s);
>>>>       return 0;
>>>
>>> Why not simply use a const AVPacket*?
>>
>> No reason. Fixed locally.
>> Thanks.
> 
> *reverted this change.
> We need to ref the packet, since we map its memory and let the GPU use
> it directly without copying the contents. 6k16bit content at 24fps is
> typically around 2Gbps when compressed, so avoiding copies is important.

How long does the hwaccel need this data?

- Andreas

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