[FFmpeg-devel] [PATCH v3 1/2] lavc/ccaption_dec: do not ignore repeated character commands

[Thierry Foucu]

Hi all

On Sun, Feb 14, 2016 at 6:11 PM, Aman Gupta <ffmpeg at tmm1.net> wrote:

> From: Aman Gupta <aman at tmm1.net>
>
> control codes in a cc stream can be repeated, and must be ignored.
> however, repeated characters must not be ignored. the code attempted to
> wipe prev_cmd in handle_char to allow repeated characters to be
> processed, but prev_cmd would previously get reset _after_ handle_char()
>
> i also moved the prev_cmd reset out from handle_char() so it can be
> re-used for special character sets, which _must_ be ignored when
> repeated.
> ---
>  libavcodec/ccaption_dec.c | 19 ++++++++++---------
>  1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/libavcodec/ccaption_dec.c b/libavcodec/ccaption_dec.c
> index 790f071..5fb2ec6 100644
> --- a/libavcodec/ccaption_dec.c
> +++ b/libavcodec/ccaption_dec.c
> @@ -484,9 +484,6 @@ static void handle_char(CCaptionSubContext *ctx, char
> hi, char lo, int64_t pts)
>      if (ctx->mode != CCMODE_POPON)
>          ctx->screen_touched = 1;
>
> -    /* reset prev command since character can repeat */
> -    ctx->prev_cmd[0] = 0;
> -    ctx->prev_cmd[1] = 0;
>      if (lo)
>         ff_dlog(ctx, "(%c,%c)\n", hi, lo);
>      else
> @@ -497,8 +494,15 @@ static void process_cc608(CCaptionSubContext *ctx,
> int64_t pts, uint8_t hi, uint
>  {
>      if (hi == ctx->prev_cmd[0] && lo == ctx->prev_cmd[1]) {
>          /* ignore redundant command */
> -    } else if ( (hi == 0x10 && (lo >= 0x40 && lo <= 0x5f)) ||
> -              ( (hi >= 0x11 && hi <= 0x17) && (lo >= 0x40 && lo <= 0x7f)
> ) ) {
> +        return;
> +    }
> +
> +    /* set prev command */
> +    ctx->prev_cmd[0] = hi;
> +    ctx->prev_cmd[1] = lo;
> +
> +    if ( (hi == 0x10 && (lo >= 0x40 && lo <= 0x5f)) ||
> +       ( (hi >= 0x11 && hi <= 0x17) && (lo >= 0x40 && lo <= 0x7f) ) ) {
>          handle_pac(ctx, hi, lo);
>      } else if ( ( hi == 0x11 && lo >= 0x20 && lo <= 0x2f ) ||
>                  ( hi == 0x17 && lo >= 0x2e && lo <= 0x2f) ) {
> @@ -559,14 +563,11 @@ static void process_cc608(CCaptionSubContext *ctx,
> int64_t pts, uint8_t hi, uint
>      } else if (hi >= 0x20) {
>          /* Standard characters (always in pairs) */
>          handle_char(ctx, hi, lo, pts);
> +        ctx->prev_cmd[0] = ctx->prev_cmd[1] = 0;
>      } else {
>          /* Ignoring all other non data code */
>          ff_dlog(ctx, "Unknown command 0x%hhx 0x%hhx\n", hi, lo);
>      }
> -
> -    /* set prev command */
> -    ctx->prev_cmd[0] = hi;
> -    ctx->prev_cmd[1] = lo;
>  }
>
>  static int decode(AVCodecContext *avctx, void *data, int *got_sub,
> AVPacket *avpkt)
> --
> 2.5.3
>
>
This commit seems to break some US broadcast CC decoding. (I can provide a
15MB sample file if needed)

Before this commit:
ffmpeg -f lavfi -i "movie=IhedxzUUxNo.ts[out0+subcc]" -map s "ts.srt"
cat ts.srt
1
00:00:01,035 --> 00:00:02,035
<font face="Monospace">FAR-RANGING IMPACT PLACES IN THE</font>

2
00:00:02,036 --> 00:00:04,466
<font face="Monospace">FAR-RANGING IMPACT PLACES IN THE
CHURCH AND AT THE LEVEL OF</font>

3
00:00:04,471 --> 00:00:06,811
<font face="Monospace">CHURCH AND AT THE LEVEL OF
POLICY ALL ACROSS THE GLOBE.</font>

4
00:00:06,807 --> 00:00:08,537
<font face="Monospace">POLICY ALL ACROSS THE GLOBE.
CERTAINLY IN THE AREA OF</font>

5
00:00:08,542 --> 00:00:10,382
<font face="Monospace">CERTAINLY IN THE AREA OF
PASTORAL CARE, I HOPE THAT IT</font>

6
00:00:10,377 --> 00:00:14,677
<font face="Monospace">PASTORAL CARE, I HOPE THAT IT
WILL LEAD TO LESS DOGMATICTI</font>

7
00:00:14,682 --> 00:00:16,352
<font face="Monospace">WILL LEAD TO LESS DOGMATICTI
INTERACTION WITH PEOPLE ACROSS A</font>

8
00:00:16,350 --> 00:00:16,920
<font face="Monospace">INTERACTION WITH PEOPLE ACROSS A
THE BOARD.</font>

9
00:00:16,917 --> 00:00:18,287
<font face="Monospace">THE BOARD.
I HOPE THAT, YOU KNOW, THERE'S</font>

10
00:00:18,285 --> 00:00:20,785
<font face="Monospace">I HOPE THAT, YOU KNOW, THERE'S
MORE OF A SENSE THAT THE CHURCH</font>



After that commit,
cat ts.srt
1
00:00:01,035 --> 00:00:02,035
<font face="Monospace">FFFARARAR-R-R-RANANANGIGIGINGNGN</font>

2
00:00:02,036 --> 00:00:04,466
<font face="Monospace">FFFARARAR-R-R-RANANANGIGIGINGNGN
CCCHUHUHURCRCRCHHH A A ANNND D D</font>

3
00:00:04,471 --> 00:00:06,811
<font face="Monospace">CCCHUHUHURCRCRCHHH A A ANNND D D
POPOPOLILILICYCYCY A A ALLLL L L</font>

4
00:00:06,807 --> 00:00:08,537
<font face="Monospace">POPOPOLILILICYCYCY A A ALLLL L L
CCCERERERTATATAINININLYLYLY I I </font>

5
00:00:08,542 --> 00:00:10,382
<font face="Monospace">CCCERERERTATATAINININLYLYLY I I
PAPAPASSSTOTOTORARARALLL C C CAA</font>

6
00:00:10,377 --> 00:00:14,677
<font face="Monospace">PAPAPASSSTOTOTORARARALLL C C CAA
WIWIWILLLLLL   LELELEADADAD   TO</font>

7
00:00:14,682 --> 00:00:16,352
<font face="Monospace">WIWIWILLLLLL   LELELEADADAD   TO
INININTETETERARARACTCTCTIOIOION </font>

8
00:00:16,350 --> 00:00:16,920
<font face="Monospace">INININTETETERARARACTCTCTIOIOION
THTHTHE E E BOBOBOAAARDRDRD...</font>

9
00:00:16,917 --> 00:00:18,287
<font face="Monospace">THTHTHE E E BOBOBOAAARDRDRD...
I I I HHHOPOPOPEEE T T THHHATATA</font>

10
00:00:18,285 --> 00:00:20,785
<font face="Monospace">I I I HHHOPOPOPEEE T T THHHATATA
MOMOMORRRE E E OFOFOF A A A   SE</font>



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