[FFmpeg-devel] [PATCH 1/2] avcodec/libzvbi-teletextdec: add support for selecting subtitle pages only

[Aman Gupta]

On Sun, May 6, 2018 at 2:05 PM, Marton Balint <cus at passwd.hu> wrote:

> Signed-off-by: Marton Balint <cus at passwd.hu>
> ---
>  doc/decoders.texi                |  5 +++--
>  libavcodec/libzvbi-teletextdec.c | 31 ++++++++++++++++++++++---------
>  2 files changed, 25 insertions(+), 11 deletions(-)
>
> diff --git a/doc/decoders.texi b/doc/decoders.texi
> index a551d5d0fd..8f07bc1afb 100644
> --- a/doc/decoders.texi
> +++ b/doc/decoders.texi
> @@ -248,8 +248,9 @@ configuration. You need to explicitly configure the
> build with
>
>  @table @option
>  @item txt_page
> -List of teletext page numbers to decode. You may use the special * string
> to
> -match all pages. Pages that do not match the specified list are dropped.
> +List of teletext page numbers to decode. Pages that do not match the
> specified
> +list are dropped. You may use the special @code{*} string to match all
> pages,
> +or @code{subtitle} to match all subtitle pages.
>

Thanks for adding this. It works as expected for me.

Might be worth documenting in the AVOption.help text as well.

Aman


>  Default value is *.
>  @item txt_chop_top
>  Discards the top teletext line. Default value is 1.
> diff --git a/libavcodec/libzvbi-teletextdec.c b/libavcodec/libzvbi-
> teletextdec.c
> index a800ad34ae..56a7182882 100644
> --- a/libavcodec/libzvbi-teletextdec.c
> +++ b/libavcodec/libzvbi-teletextdec.c
> @@ -73,6 +73,7 @@ typedef struct TeletextContext
>      vbi_sliced      sliced[MAX_SLICES];
>
>      int             readorder;
> +    uint8_t         subtitle_map[2048];
>  } TeletextContext;
>
>  static int chop_spaces_utf8(const unsigned char* t, int len)
> @@ -281,16 +282,14 @@ static void handler(vbi_event *ev, void *user_data)
>      vbi_page page;
>      int res;
>      char pgno_str[12];
> -    vbi_subno subno;
> -    vbi_page_type vpt;
>      int chop_top;
> -    char *lang;
> +    int is_subtitle_page = ctx->subtitle_map[ev->ev.ttx_page.pgno &
> 0x7ff];
>
>      snprintf(pgno_str, sizeof pgno_str, "%03x", ev->ev.ttx_page.pgno);
>      av_log(ctx, AV_LOG_DEBUG, "decoded page %s.%02x\n",
>             pgno_str, ev->ev.ttx_page.subno & 0xFF);
>
> -    if (strcmp(ctx->pgno, "*") && !strstr(ctx->pgno, pgno_str))
> +    if (strcmp(ctx->pgno, "*") && (strcmp(ctx->pgno, "subtitle") ||
> !is_subtitle_page) && !strstr(ctx->pgno, pgno_str))
>          return;
>      if (ctx->handler_ret < 0)
>          return;
> @@ -303,9 +302,7 @@ static void handler(vbi_event *ev, void *user_data)
>      if (!res)
>          return;
>
> -    vpt = vbi_classify_page(ctx->vbi, ev->ev.ttx_page.pgno, &subno,
> &lang);
> -    chop_top = ctx->chop_top ||
> -        ((page.rows > 1) && (vpt == VBI_SUBTITLE_PAGE));
> +    chop_top = ctx->chop_top || ((page.rows > 1) && is_subtitle_page);
>
>      av_log(ctx, AV_LOG_DEBUG, "%d x %d page chop:%d\n",
>             page.columns, page.rows, chop_top);
> @@ -357,11 +354,26 @@ static int slice_to_vbi_lines(TeletextContext *ctx,
> uint8_t* buf, int size)
>              else {
>                  int line_offset  = buf[2] & 0x1f;
>                  int field_parity = buf[2] & 0x20;
> -                int i;
> +                uint8_t *p = ctx->sliced[lines].data;
> +                int i, pmag;
>                  ctx->sliced[lines].id = VBI_SLICED_TELETEXT_B;
>                  ctx->sliced[lines].line = (line_offset > 0 ? (line_offset
> + (field_parity ? 0 : 313)) : 0);
>                  for (i = 0; i < 42; i++)
> -                    ctx->sliced[lines].data[i] = vbi_rev8(buf[4 + i]);
> +                    p[i] = vbi_rev8(buf[4 + i]);
> +                /* Unfortunately libzvbi does not expose page flags, and
> +                 * vbi_classify_page only checks MIP, so we have to
> manually
> +                 * decode the page flags and store the results. */
> +                pmag = vbi_unham16p(p);
> +                if (pmag >= 0 && pmag >> 3 == 0) {   // We found a row 0
> header
> +                    int page = vbi_unham16p(p + 2);
> +                    int flags1 = vbi_unham16p(p + 6);
> +                    int flags2 = vbi_unham16p(p + 8);
> +                    if (page >= 0 && flags1 >= 0 && flags2 >= 0) {
> +                        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);
> +                    }
> +                }
>                  lines++;
>              }
>          }
> @@ -502,6 +514,7 @@ static int teletext_close_decoder(AVCodecContext
> *avctx)
>      vbi_decoder_delete(ctx->vbi);
>      ctx->vbi = NULL;
>      ctx->pts = AV_NOPTS_VALUE;
> +    memset(ctx->subtitle_map, 0, sizeof(ctx->subtitle_map));
>      if (!(avctx->flags2 & AV_CODEC_FLAG2_RO_FLUSH_NOOP))
>          ctx->readorder = 0;
>      return 0;
> --
> 2.13.6
>
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