[FFmpeg-devel] [PATCH v2] avcodec/ccaption_dec: honor transparency of leading non-breaking space

[Stefano Sabatini]

On date Sunday 2024-03-10 19:44:11 -0500, Marth64 wrote:
> In Closed Captions (US), the non-breaking space (0xA0) can be used to align
> text horizontally from the left by using it as a leading character.
> However, CC decoder does not ignore it as a leading character like it does
> an ordinary space, so a blank padding is rendered over the black CC box.
> This is not the intended viewing experience.
> 
> Ignore the leading non-breaking spaces, thus creating the intended transparency
> which aligns the text. Since all characters are fixed-width in CC, it
> can be handled the same way as we currently treat leading ordinary spaces.
> Also, as a nit, lowercase the NBSP's hex code in the entry table to match
> casing of the other hex codes.
> 
> v2 only updates the commit message which mistakenly referenced avformat.
> 
> Signed-off-by: Marth64 <marth64 at proxyid.net>
> ---
>  libavcodec/ccaption_dec.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/libavcodec/ccaption_dec.c b/libavcodec/ccaption_dec.c
> index faf058ce97..591013d202 100644
> --- a/libavcodec/ccaption_dec.c
> +++ b/libavcodec/ccaption_dec.c
> @@ -91,7 +91,7 @@ enum cc_charset {
>          ENTRY(0x36, "\u00a3")                            \
>          ENTRY(0x37, "\u266a")                            \
>          ENTRY(0x38, "\u00e0")                            \
> -        ENTRY(0x39, "\u00A0")                            \
> +        ENTRY(0x39, "\u00a0")                            \
>          ENTRY(0x3a, "\u00e8")                            \
>          ENTRY(0x3b, "\u00e2")                            \
>          ENTRY(0x3c, "\u00ea")                            \
> @@ -471,7 +471,8 @@ static int capture_screen(CCaptionSubContext *ctx)
>              const char *row = screen->characters[i];
>              const char *charset = screen->charsets[i];
>              j = 0;
> -            while (row[j] == ' ' && charset[j] == CCSET_BASIC_AMERICAN)
> +            while ((row[j] == ' '  && charset[j] == CCSET_BASIC_AMERICAN) ||
> +                   (row[j] == 0x39 && charset[j] == CCSET_SPECIAL_AMERICAN))
>                  j++;
>              if (!tab || j < tab)
>                  tab = j;
> @@ -491,7 +492,9 @@ static int capture_screen(CCaptionSubContext *ctx)
>              j = 0;
>  
>              /* skip leading space */
> -            while (row[j] == ' ' && charset[j] == CCSET_BASIC_AMERICAN && j < tab)
> +            while (j < tab &&
> +                   (row[j] == ' '  && charset[j] == CCSET_BASIC_AMERICAN) ||
> +                   (row[j] == 0x39 && charset[j] == CCSET_SPECIAL_AMERICAN))
>                  j++;

Patch LGTM, will apply the complete patcheset if I see no comments
after a few days.

Thanks.