[FFmpeg-devel] [PATCH] avcodec/ccaption_dec: don't print multiple \pos tags per cue

[FFmpeg-devel] [PATCH] avcodec/ccaption_dec: don't print multiple \pos tags per cue

[Marth64]

Currently, Closed Captions decoder prints multiple \pos ASS tags per line,
per cue. This is invalid behavior, because only the first \pos tag in a cue
is honored by ASS anyway. Don't write multiple \pos tags.

Signed-off-by: Marth64 <marth64@proxyid.net>
---
 libavcodec/ccaption_dec.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 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;
+            }
 
             for (; j < SCREEN_COLUMNS; j++) {
                 const char *e_tag = "", *s_tag = "", *c_tag = "", *b_tag = "";
-- 
2.34.1

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Re: [FFmpeg-devel] [PATCH] avcodec/ccaption_dec: don't print multiple \pos tags per cue

[Stefano Sabatini]

On date Sunday 2024-03-10 19:40:47 -0500, Marth64 wrote:
> Currently, Closed Captions decoder prints multiple \pos ASS tags per line,
> per cue. This is invalid behavior, because only the first \pos tag in a cue
> is honored by ASS anyway. Don't write multiple \pos tags.
> 
> Signed-off-by: Marth64 <marth64@proxyid.net>
> ---
>  libavcodec/ccaption_dec.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 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;
> +            }
>  
>              for (; j < SCREEN_COLUMNS; j++) {
>                  const char *e_tag = "", *s_tag = "", *c_tag = "", *b_tag = "";

LGTM, thanks.
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Re: [FFmpeg-devel] [PATCH] avcodec/ccaption_dec: don't print multiple \pos tags per cue

[Michael Niedermayer]

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On Sun, Mar 10, 2024 at 07:40:47PM -0500, Marth64 wrote:
> Currently, Closed Captions decoder prints multiple \pos ASS tags per line,
> per cue. This is invalid behavior, because only the first \pos tag in a cue
> is honored by ASS anyway. Don't write multiple \pos tags.
> 
> Signed-off-by: Marth64 <marth64@proxyid.net>
> ---
>  libavcodec/ccaption_dec.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)

This breaks fate

--- ./tests/ref/fate/sub-cc-scte20	2024-03-05 02:37:36.223299993 +0100
+++ tests/data/fate/sub-cc-scte20	2024-03-11 22:13:08.091910294 +0100
@@ -13,5 +13,5 @@
 [Events]
 Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
 Dialogue: 0,0:00:00.00,0:00:01.44,Default,,0,0,0,,{\an7}{\pos(48,182)}BESIDES THE
-Dialogue: 0,0:00:01.43,0:00:03.93,Default,,0,0,0,,{\an7}{\pos(38,166)}\hBESIDES THE \N{\an7}{\pos(38,197)}SPENDING AND THIS, IS THAT CAR
-Dialogue: 0,0:00:03.94,0:00:06.31,Default,,0,0,0,,{\an7}{\pos(38,182)}SPENDING AND THIS, IS THAT CAR \N{\an7}{\pos(38,197)}MANUFACTURERS ARE ABOUT AS
+Dialogue: 0,0:00:01.43,0:00:03.93,Default,,0,0,0,,{\an7}{\pos(38,166)}\hBESIDES THE \NSPENDING AND THIS, IS THAT CAR
+Dialogue: 0,0:00:03.94,0:00:06.31,Default,,0,0,0,,{\an7}{\pos(38,182)}SPENDING AND THIS, IS THAT CAR \NMANUFACTURERS ARE ABOUT AS
Test sub-cc-scte20 failed. Look at tests/data/fate/sub-cc-scte20.err for details.

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Nations do behave wisely once they have exhausted all other alternatives. 
-- Abba Eban

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Re: [FFmpeg-devel] [PATCH] avcodec/ccaption_dec: don't print multiple \pos tags per cue

[Marth64]

> This breaks fate
Looking into it - thanks.

PS, sorry for previous top-posting in replies. Will be more cautious of
that.
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Re: [FFmpeg-devel] [PATCH] avcodec/ccaption_dec: don't print multiple \pos tags per cue

[Leo Izen]

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On 3/11/24 17:48, Marth64 wrote:
>> This breaks fate
> Looking into it - thanks.
> 

It is possible that the change is correct, and that the fate test needs 
to be changed to reflect the correct behavior. Not necessarily, but 
possibly.

- Leo Izen (Traneptora)


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Re: [FFmpeg-devel] [PATCH] avcodec/ccaption_dec: don't print multiple \pos tags per cue

[Marth64]

Thanks, will follow up with a v3 set (consolidating/resolving feedback on
the other CC fixes as well).
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