[FFmpeg-devel] [PATCH v3 2/6] avcodec/ccaption_dec: don't print multiple \an and \pos tags

[Stefano Sabatini]

On date Tuesday 2024-03-12 01:00:01 -0500, Marth64 wrote:
> Closed Captions decoder prints multiple \pos ASS tags per cue,
> and preceding the \pos tag is a fixed \an7 that fixes rendering
> position from the top left corner and enforces justification.
> 
> Printing multiple \an and \pos tags in this way is invalid behavior,
> because only the first \pos tag in a cue is honored by ASS anyway.
> Don't write multiple \an and \pos tags.
> 
> Also, update tests accordingly.
> 
> Signed-off-by: Marth64 <marth64 at proxyid.net>
> ---
>  libavcodec/ccaption_dec.c      |   8 +-
>  tests/ref/fate/sub-cc          |   2 +-
>  tests/ref/fate/sub-cc-realtime |   8 +-
>  tests/ref/fate/sub-cc-scte20   |   4 +-
>  tests/ref/fate/sub-scc         | 146 ++++++++++++++++-----------------
>  5 files changed, 86 insertions(+), 82 deletions(-)
> 
> diff --git a/libavcodec/ccaption_dec.c b/libavcodec/ccaption_dec.c
> index faf058ce97..9d4a93647c 100644
> --- a/libavcodec/ccaption_dec.c
> +++ b/libavcodec/ccaption_dec.c
> @@ -456,7 +456,7 @@ static void roll_up(CCaptionSubContext *ctx)
>  
>  static int capture_screen(CCaptionSubContext *ctx)
>  {
> -    int i, j, tab = 0;
> +    int i, j, tab = 0, seen_row = 0;
>      struct Screen *screen = ctx->screen + ctx->active_screen;
>      enum cc_font prev_font = CCFONT_REGULAR;
>      enum cc_color_code prev_color = CCCOL_WHITE;
> @@ -496,7 +496,11 @@ static int capture_screen(CCaptionSubContext *ctx)
>  
>              x = ASS_DEFAULT_PLAYRESX * (0.1 + 0.0250 * j);
>              y = ASS_DEFAULT_PLAYRESY * (0.1 + 0.0533 * i);
> -            av_bprintf(&ctx->buffer[bidx], "{\\an7}{\\pos(%d,%d)}", x, y);
> +
> +            if (!seen_row) {
> +                av_bprintf(&ctx->buffer[bidx], "{\\an7}{\\pos(%d,%d)}", x, y);
> +                seen_row = 1;
> +            }

probably it might be useful to print debug logs in case the pos
coordinates are found but not rendered?

[...]

LGTM otherwise.