[vlc-devel] [PATCH] fps: hold the extra pictures we send

[Steve Lhomme]

On 2020-09-29 17:02, Rémi Denis-Courmont wrote:
> Le tiistaina 29. syyskuuta 2020, 8.36.26 EEST Steve Lhomme a écrit :
>> The same picture is supposed to be filtered or rendered at a different date,
>> but the pixels should be the same. The content is not going to be changed
>> in the pictures we output from this filter.
>> ---
>>   modules/video_filter/fps.c | 5 +----
>>   1 file changed, 1 insertion(+), 4 deletions(-)
>>
>> diff --git a/modules/video_filter/fps.c b/modules/video_filter/fps.c
>> index 4e6a59dfd66..5dffffe4d35 100644
>> --- a/modules/video_filter/fps.c
>> +++ b/modules/video_filter/fps.c
>> @@ -116,10 +116,7 @@ static picture_t *Filter( filter_t *p_filter, picture_t
>> *p_picture) should be avoided, it's only here as filter should work in that
>> direction too*/ while( unlikely( (date_Get( &p_sys->next_output_pts ) +
>> p_sys->i_output_frame_interval ) < p_picture->date ) ) {
>> -        picture_t *p_tmp = NULL;
>> -        p_tmp = picture_NewFromFormat( &p_filter->fmt_out.video );
>> -
>> -        picture_Copy( p_tmp, p_sys->p_previous_pic);
>> +        picture_t *p_tmp = picture_Hold( p_sys->p_previous_pic );
>>           p_tmp->date = date_Get( &p_sys->next_output_pts );
>>
>>           last_pic = vlc_picture_chain_Append( &p_sys->p_previous_pic,
>> last_pic, p_tmp );
> 
> Filters assume that their input picture is not shared, and are conversely not
> allowed to provide a shared picture on output.

That doesn't like everything I've seen in filters. Why would there be 
such a backward rule ? You must *never* change the input content of a 
video filter (it could damage reference frames in the decoder). So 
whether the content is shared or not between picture should have zero 
impact.

> Holding a picture like this would work if VLC implemented a systematic copy-
> on-write policy, but AFAIK it does not at this time.
> 
> -- 
> Реми Дёни-Курмон
> http://www.remlab.net/
> 
> 
> 
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