Re: [FFmpeg-devel] [PATCH] avcodec/webvttdec: strip classes

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Leon Grutters:
> If a supported tag has a class, e.g "<i.bold>" it is ignored entirely;
> so for example "<i.bold>Hello</i>" would be converted to "Hello{\i0}"
> instead of the intended "{\i1}Hello{\i0}".
> 
> Signed-off-by: Leon Grutters <gruttersleonbot2@gmail.com>
> ---
>  libavcodec/webvttdec.c | 51 +++++++++++++++++++++++++++++++++---------
>  1 file changed, 40 insertions(+), 11 deletions(-)
> 
> diff --git a/libavcodec/webvttdec.c b/libavcodec/webvttdec.c
> index 35bdbe805d..4111d138c4 100644
> --- a/libavcodec/webvttdec.c
> +++ b/libavcodec/webvttdec.c
> @@ -29,25 +29,53 @@
>  #include "ass.h"
>  #include "codec_internal.h"
>  #include "libavutil/bprint.h"
> +#include "libavutil/mem.h"
>  
>  static const struct {
>      const char *from;
>      const char *to;
>  } webvtt_tag_replace[] = {
> -    {"<i>", "{\\i1}"}, {"</i>", "{\\i0}"},
> -    {"<b>", "{\\b1}"}, {"</b>", "{\\b0}"},
> -    {"<u>", "{\\u1}"}, {"</u>", "{\\u0}"},
>      {"{", "\\{{}"}, {"\\", "\\\xe2\x81\xa0"}, // escape to avoid ASS markup conflicts
>      {"&gt;", ">"}, {"&lt;", "<"},
>      {"&lrm;", "\xe2\x80\x8e"}, {"&rlm;", "\xe2\x80\x8f"},
>      {"&amp;", "&"}, {"&nbsp;", "\\h"},
>  };
> +static const struct {
> +    const char *from;
> +    const char *to;
> +} webvtt_valid_tags[] = {
> +    {"i", "{\\i1}"}, {"/i", "{\\i0}"},
> +    {"b", "{\\b1}"}, {"/b", "{\\b0}"},
> +    {"u", "{\\u1}"}, {"/u", "{\\u0}"},
> +};

These strings are so small that one can avoid the relocations by using
fixes-size buffers.

>  
>  static int webvtt_event_to_ass(AVBPrint *buf, const char *p)
>  {
> -    int i, again = 0, skip = 0;
> +    int i, again = 0/*, skip = 0*/;
>  
>      while (*p) {
> +        if (*p == '<') {
> +            const char *tag_end = strchr(p, '>');
> +            char *tag_body, *tag_name, *saveptr = NULL;
> +            ptrdiff_t len;
> +            if (!tag_end)
> +                break;
> +            len = tag_end - p + 1;
> +            tag_body = av_strndup(p + 1, len - 2);
> +            if (!tag_body)
> +                return AVERROR(ENOMEM);

This allocation seems unnecessary. You can inspect the string without
modifying it by using strncmp() below and by using a maximum field width
for the %s directive in a parameter.

> +            tag_name = av_strtok(tag_body, ".", &saveptr);
> +            for (i = 0; i < FF_ARRAY_ELEMS(webvtt_valid_tags); i++) {
> +                const char *from = webvtt_valid_tags[i].from;
> +                if(!strcmp(tag_name, from)) {
> +                    av_bprintf(buf, "%s", webvtt_valid_tags[i].to);
> +                    break;
> +                }
> +            }
> +            p += len;
> +            again = 1;
> +            av_freep(&tag_body);
> +        }
>  
>          for (i = 0; i < FF_ARRAY_ELEMS(webvtt_tag_replace); i++) {
>              const char *from = webvtt_tag_replace[i].from;
> @@ -59,21 +87,22 @@ static int webvtt_event_to_ass(AVBPrint *buf, const char *p)
>                  break;
>              }
>          }
> +
>          if (!*p)
>              break;
>  
>          if (again) {
>              again = 0;
> -            skip = 0;
> +            // skip = 0;
>              continue;
>          }
> -        if (*p == '<')
> -            skip = 1;
> -        else if (*p == '>')
> -            skip = 0;
> -        else if (p[0] == '\n' && p[1])
> +        // if (*p == '<')
> +        //     skip = 1;
> +        // else if (*p == '>')
> +        //     skip = 0;
> +        if (p[0] == '\n' && p[1])
>              av_bprintf(buf, "\\N");
> -        else if (!skip && *p != '\r')
> +        else if (/*!skip && */*p != '\r')
>              av_bprint_chars(buf, *p, 1);
>          p++;
>      }

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