[FFmpeg-devel] [PATCH] avcodec/av1dec: fix loading PrevGmParams for frames with primary_ref_frame none

[Mark Thompson]

On 27/10/2020 21:01, James Almer wrote:
> On 10/27/2020 5:57 PM, Mark Thompson wrote:
>> On 17/10/2020 20:30, James Almer wrote:
>>> Signed-off-by: James Almer <jamrial at gmail.com>
>>> ---
>>>    libavcodec/av1dec.c | 9 +++++++--
>>>    1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/libavcodec/av1dec.c b/libavcodec/av1dec.c
>>> index 54aeba1812..04aaf5d148 100644
>>> --- a/libavcodec/av1dec.c
>>> +++ b/libavcodec/av1dec.c
>>> @@ -109,13 +109,18 @@ static void read_global_param(AV1DecContext *s,
>>> int type, int ref, int idx)
>>>    {
>>>        uint8_t primary_frame, prev_frame;
>>>        uint32_t abs_bits, prec_bits, round, prec_diff, sub, mx;
>>> -    int32_t r;
>>> +    int32_t r, prev_gm_param;
>>>          primary_frame = s->raw_frame_header->primary_ref_frame;
>>>        prev_frame = s->raw_frame_header->ref_frame_idx[primary_frame];
>>>        abs_bits = AV1_GM_ABS_ALPHA_BITS;
>>>        prec_bits = AV1_GM_ALPHA_PREC_BITS;
>>>    +    if (s->raw_frame_header->primary_ref_frame ==
>>> AV1_PRIMARY_REF_NONE)
>>> +        prev_gm_param = s->cur_frame.gm_params[ref][idx];
>>
>> To clarify that I'm reading the standard correctly here, this is the
>> value set for PrevGmParams by setup_past_independance(), which then
>> matches the default for gm_params at the top of global_motion_params()
>> so you've reused it here?
> 
> Correct. Assuming s->cur_frame.gm_params will contain the default values
> when primary_ref_frame == AV1_PRIMARY_REF_NONE (as it happens in
> global_motion_params()) simplifies the code quite a bit. Otherwise I'd
> have to add some array with said defaults somewhere.

Do you mind adding a little comment saying that?  It took me quite a few minutes of staring at it thinking it was wrong to realise what was going on.

>>
>>> +    else
>>> +        prev_gm_param = s->ref[prev_frame].gm_params[ref][idx];
>>> +
>>>        if (idx < 2) {
>>>            if (type == AV1_WARP_MODEL_TRANSLATION) {
>>>                abs_bits = AV1_GM_ABS_TRANS_ONLY_BITS -
>>> @@ -131,7 +136,7 @@ static void read_global_param(AV1DecContext *s,
>>> int type, int ref, int idx)
>>>        prec_diff = AV1_WARPEDMODEL_PREC_BITS - prec_bits;
>>>        sub = (idx % 3) == 2 ? (1 << prec_bits) : 0;
>>>        mx = 1 << abs_bits;
>>> -    r = (s->ref[prev_frame].gm_params[ref][idx] >> prec_diff) - sub;
>>> +    r = (prev_gm_param >> prec_diff) - sub;
>>>          s->cur_frame.gm_params[ref][idx] =
>>>           
>>> (decode_signed_subexp_with_ref(s->raw_frame_header->gm_params[ref][idx],
>>>

LGTM with that.

Thanks,

- Mark