[vlc-devel] [PATCH 1/2] nvdec: add chroma and depth fallback

[Steve Lhomme]

On the other hand we may use this "delayed" behavior if nvdec is the 
forced decoder. But that's not how most people are going to use it.

On 2020-04-07 7:52, Steve Lhomme wrote:
> I don't think this is correct. If we can't tell the video format during 
> Open, there is no way to tell if we will be able to decode the stream or 
> not. So we may be selected as the decoder but in the end we can't decode 
> the video. At this point it's too late to fallback to a more suitable 
> decoder (libavcodec).
> 
> That's a drawback of the nvdec decoder until we can restart decoders 
> without losing data for the next decoder (if that ever happens). That's 
> also a reason why nvdec can have a higher priority than libavcodec, 
> because it will fallback properly.
> 
> On 2020-04-06 15:02, quentin.chateau at deepskycorp.com wrote:
>> From: Quentin Chateau <quentin.chateau at deepskycorp.com>
>>
>> When the chroma and depth is unknown to the hxxx_helper,
>> fallback to the common 4:2:0 8bits format as initial value.
>> The decoder may change these values later on.
>> ---
>>   modules/hw/nvdec/nvdec.c | 20 ++++++++++++--------
>>   1 file changed, 12 insertions(+), 8 deletions(-)
>>
>> diff --git a/modules/hw/nvdec/nvdec.c b/modules/hw/nvdec/nvdec.c
>> index e3aeff2355..ca28522d32 100644
>> --- a/modules/hw/nvdec/nvdec.c
>> +++ b/modules/hw/nvdec/nvdec.c
>> @@ -923,15 +923,19 @@ static int OpenDecoder(vlc_object_t *p_this)
>>       // try different output
>>       if (p_sys->b_is_hxxx)
>>       {
>> -        uint8_t i_chroma_idc, i_depth_chroma;
>> -        result = hxxx_helper_get_chroma_chroma(&p_sys->hh, 
>> &i_chroma_idc,
>> -                                            &i_depth_luma, 
>> &i_depth_chroma);
>> -        if (result != VLC_SUCCESS) {
>> -            if (p_sys->b_is_hxxx)
>> -                hxxx_helper_clean(&p_sys->hh);
>> -            return VLC_EGENERIC;
>> +        uint8_t hxxx_chroma_idc, hxxx_depth_chroma, hxxx_depth_luma;
>> +        result = hxxx_helper_get_chroma_chroma(&p_sys->hh, 
>> &hxxx_chroma_idc,
>> +                                            &hxxx_depth_luma, 
>> &hxxx_depth_chroma);
>> +        if (result == VLC_SUCCESS)
>> +        {
>> +            i_depth_luma = hxxx_depth_luma;
>> +            cudaChroma = MapChomaIDC(hxxx_chroma_idc);
>> +        }
>> +        else
>> +        {
>> +            cudaChroma = cudaVideoChromaFormat_420;
>> +            i_depth_luma = 8;
>>           }
>> -        cudaChroma = MapChomaIDC(i_chroma_idc);
>>           unsigned i_w, i_h, i_vw, i_vh;
>>           result = hxxx_helper_get_current_picture_size(&p_sys->hh, 
>> &i_w, &i_h, &i_vw, &i_vh);
>> -- 
>> 2.17.1
>>
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