[vlc-devel] [PATCH 1/9] video_format: add the number of fields per picture in the video format

[Romain Vimont]

On Mon, Nov 16, 2020 at 01:44:12PM +0100, Steve Lhomme wrote:
> In general it's 2 fields. If the number of fields changes in the source, the
> (deinterlacing) filters should be updated.
> 
> By default the video format is progressive and the i_num_fields can be ignored.
> It should be set to 2 for progressive to be consistent with how the value was
> set so far.
> 
> This field is more stable than the picture i_nb_fields that also included
> repeated fields and pictures. It only contains the information about the
> number of fields in each actual picture.
> ---
>  include/vlc_es.h                      | 3 +++
>  modules/visualization/visual/visual.c | 1 +
>  2 files changed, 4 insertions(+)
> 
> diff --git a/include/vlc_es.h b/include/vlc_es.h
> index 404a937d833..459d16b3c37 100644
> --- a/include/vlc_es.h
> +++ b/include/vlc_es.h
> @@ -376,6 +376,8 @@ struct video_format_t
>      video_multiview_mode_t multiview_mode;        /** Multiview mode, 2D, 3D */
>      bool b_multiview_right_eye_first;   /** Multiview left or right eye first*/
>  
> +    unsigned int    i_num_fields;          /**< number of fields per picture */

I think there are only 2 cases:
 - either all fields are interleaved in a single picture
 - either the fields are split into separate pictures

So IMO using an integer adds complexity (more cases to handle) for no
reason. I suggest something like a 'bool interlaced_split_fields'
instead.

Also, the interlaced/progressive flag should also be in the
video_format_t (as you suggested in another thread): having 1 field when
the video is progressive is not the same as having 1 field when the
video is interlaced.

Regards

> +
>      video_projection_mode_t projection_mode;            /**< projection mode */
>      vlc_viewpoint_t pose;
>      struct {
> @@ -402,6 +404,7 @@ static inline void video_format_Init( video_format_t *p_src, vlc_fourcc_t i_chro
>  {
>      memset( p_src, 0, sizeof( video_format_t ) );
>      p_src->i_chroma = i_chroma;
> +    p_src->i_num_fields = 2;
>      vlc_viewpoint_init( &p_src->pose );
>  }
>  
> diff --git a/modules/visualization/visual/visual.c b/modules/visualization/visual/visual.c
> index 13343d0f045..8a35b0ddcc6 100644
> --- a/modules/visualization/visual/visual.c
> +++ b/modules/visualization/visual/visual.c
> @@ -309,6 +309,7 @@ static int Open( vlc_object_t *p_this )
>          .transfer = TRANSFER_FUNC_SRGB,
>          .primaries = COLOR_PRIMARIES_SRGB,
>          .space = COLOR_SPACE_SRGB,
> +        .i_num_fields = 2,
>      };
>      p_sys->p_vout = aout_filter_GetVout( p_filter, &fmt );
>      if( p_sys->p_vout == NULL )
> -- 
> 2.26.2
> 
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