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

[James Almer]

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.

> 
>> +    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],
>>
> 
> - Mark
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