Re: [FFmpeg-devel] [PATCH] avcodec/hevc_ps: allocate only the required HEVCHdrParams within a VPS

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

James Almer:
> On 3/21/2024 8:15 AM, Andreas Rheinhardt wrote:
>> James Almer:
>>> Signed-off-by: James Almer <jamrial@gmail.com>
>>> ---
>>>   libavcodec/hevc_ps.c     | 17 +++++++++++++++--
>>>   libavcodec/hevc_ps.h     |  2 +-
>>>   libavcodec/vulkan_hevc.c |  2 +-
>>>   3 files changed, 17 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/libavcodec/hevc_ps.c b/libavcodec/hevc_ps.c
>>> index 20ceb09829..d3edc0810d 100644
>>> --- a/libavcodec/hevc_ps.c
>>> +++ b/libavcodec/hevc_ps.c
>>> @@ -442,13 +442,21 @@ static int decode_hrd(GetBitContext *gb, int
>>> common_inf_present,
>>>       return 0;
>>>   }
>>>   +static void uninit_vps(FFRefStructOpaque opaque, void *obj)
>>> +{
>>> +    HEVCVPS *vps = obj;
>>> +
>>> +    for (int i = 0; i < vps->vps_num_hrd_parameters; i++)
>>> +        ff_refstruct_unref(&vps->hdr[i]);
>>> +}
>>> +
>>>   int ff_hevc_decode_nal_vps(GetBitContext *gb, AVCodecContext *avctx,
>>>                              HEVCParamSets *ps)
>>>   {
>>>       int i,j;
>>>       int vps_id = 0;
>>>       ptrdiff_t nal_size;
>>> -    HEVCVPS *vps = ff_refstruct_allocz(sizeof(*vps));
>>> +    HEVCVPS *vps = ff_refstruct_alloc_ext(sizeof(*vps), 0, NULL,
>>> uninit_vps);
>>>         if (!vps)
>>>           return AVERROR(ENOMEM);
>>> @@ -538,12 +546,17 @@ int ff_hevc_decode_nal_vps(GetBitContext *gb,
>>> AVCodecContext *avctx,
>>>               goto err;
>>>           }
>>>           for (i = 0; i < vps->vps_num_hrd_parameters; i++) {
>>> +            HEVCHdrParams *hdr = ff_refstruct_allocz(sizeof(*hdr));
>>>               int common_inf_present = 1;
>>>   +            if (!hdr)
>>> +                return AVERROR(ENOMEM);
>>> +
>>>               get_ue_golomb_long(gb); // hrd_layer_set_idx
>>>               if (i)
>>>                   common_inf_present = get_bits1(gb);
>>> -            decode_hrd(gb, common_inf_present, &vps->hdr[i],
>>> +
>>> +            decode_hrd(gb, common_inf_present, hdr,
>>>                          vps->vps_max_sub_layers);
>>>           }
>>
>> Why do you allocate the HEVCHdrParams separately when you know
>> vps_num_hrd_parameters before allocating the first one?
> 
> You want me to allocate all of them with a single ff_refstruct_allocz()
> and store individual pointers for each?
> 

No, I want you to allocate them jointly and access them via "const
HEVCHdrParams *src = &vps->hdr[i]".
(Removing the individual pointers is precisely the point.)
Furthermore, there is no reason to allocate it via RefStruct. A simple
av_calloc() is enough (they have one owner: The containing HEVCVPS; that
said HEVCVPS can have multiple owners doesn't change this).

>>
>>>       }
>>> diff --git a/libavcodec/hevc_ps.h b/libavcodec/hevc_ps.h
>>> index 9cdec9b6c1..ff94f90a5e 100644
>>> --- a/libavcodec/hevc_ps.h
>>> +++ b/libavcodec/hevc_ps.h
>>> @@ -150,7 +150,7 @@ typedef struct PTL {
>>>     typedef struct HEVCVPS {
>>>       unsigned int vps_id;
>>> -    HEVCHdrParams hdr[HEVC_MAX_LAYER_SETS];
>>> +    HEVCHdrParams *hdr[HEVC_MAX_LAYER_SETS];
>>>         uint8_t vps_temporal_id_nesting_flag : 1;
>>>       uint8_t vps_sub_layer_ordering_info_present_flag : 1;
>>> diff --git a/libavcodec/vulkan_hevc.c b/libavcodec/vulkan_hevc.c
>>> index 239bff75e5..a89d09a372 100644
>>> --- a/libavcodec/vulkan_hevc.c
>>> +++ b/libavcodec/vulkan_hevc.c
>>> @@ -563,7 +563,7 @@ static void set_vps(const HEVCVPS *vps,
>>>                       HEVCHeaderVPSSet sls[])
>>>   {
>>>       for (int i = 0; i < vps->vps_num_hrd_parameters; i++) {
>>> -        const HEVCHdrParams *src = &vps->hdr[i];
>>> +        const HEVCHdrParams *src = vps->hdr[i];
>>>             sls_hdr[i] = (StdVideoH265HrdParameters) {
>>>               .flags = (StdVideoH265HrdFlags) {
>>
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