[FFmpeg-devel] [PATCH] avcodec/libzvbi-teletextdec: propagate ERASE_PAGE flag for repeated subtitle page headers

[Marton Balint]

On Mon, 11 Jun 2018, Marton Balint wrote:

> This works around a libzvbi bug (a corner case in the teletext spec):
>
> https://sourceforge.net/p/zapping/bugs/203/
> https://sourceforge.net/p/zapping/patches/20/
>
> Fixes samples/ffmpeg-bugs/trac/ticket2086/RBT_20100801_1835.ts.
>
> Signed-off-by: Marton Balint <cus at passwd.hu>
> ---
> libavcodec/libzvbi-teletextdec.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/libavcodec/libzvbi-teletextdec.c b/libavcodec/libzvbi-teletextdec.c
> index ccded23e7c..809547545b 100644
> --- a/libavcodec/libzvbi-teletextdec.c
> +++ b/libavcodec/libzvbi-teletextdec.c
> @@ -74,6 +74,8 @@ typedef struct TeletextContext
>
>     int             readorder;
>     uint8_t         subtitle_map[2048];
> +    int             last_pgno;
> +    int             last_p5;
> } TeletextContext;
> 
> static int chop_spaces_utf8(const unsigned char* t, int len)
> @@ -372,6 +374,17 @@ static int slice_to_vbi_lines(TeletextContext *ctx, uint8_t* buf, int size)
>                         int pgno = ((pmag & 7) << 8) + page;
>                         // Check for disabled NEWSFLASH flag and enabled SUBTITLE and SUPRESS_HEADER flags
>                         ctx->subtitle_map[pgno] = (!(flags1 & 0x40) && flags1 & 0x80 && flags2 & 0x01);
> +                        // Propagate ERASE_PAGE flag for repeated page headers to work around a libzvbi bug
> +                        if (ctx->subtitle_map[pgno] && pgno == ctx->last_pgno) {
> +                            int last_byte9 = vbi_unham8(ctx->last_p5);
> +                            if (last_byte9 >= 0 && last_byte9 & 0x8) {
> +                                int byte9 = vbi_unham8(p[5]);
> +                                if (byte9 >= 0)
> +                                    p[5] = vbi_ham8(byte9 | 0x8);
> +                            }
> +                        }
> +                        ctx->last_pgno = pgno;
> +                        ctx->last_p5 = p[5];
>                     }
>                 }
>                 lines++;
> @@ -494,6 +507,7 @@ static int teletext_init_decoder(AVCodecContext *avctx)
>
>     ctx->vbi = NULL;
>     ctx->pts = AV_NOPTS_VALUE;
> +    ctx->last_pgno = -1;
>
>     if (ctx->opacity == -1)
>         ctx->opacity = ctx->transparent_bg ? 0 : 255;
> @@ -514,6 +528,7 @@ static int teletext_close_decoder(AVCodecContext *avctx)
>     vbi_decoder_delete(ctx->vbi);
>     ctx->vbi = NULL;
>     ctx->pts = AV_NOPTS_VALUE;
> +    ctx->last_pgno = -1;
>     memset(ctx->subtitle_map, 0, sizeof(ctx->subtitle_map));
>     if (!(avctx->flags2 & AV_CODEC_FLAG2_RO_FLUSH_NOOP))
>         ctx->readorder = 0;
> --

Pushed.

Regards,
Marton