Re: [FFmpeg-devel] [PATCH] avfilter/vf_subtitles: add an option to choose sub stream by language

[Marton Balint <cus@passwd.hu>]

On Tue, 19 Apr 2022, James Darnley wrote:

> ---
> doc/filters.texi           |  5 +++++
> libavfilter/vf_subtitles.c | 23 ++++++++++++++++++++---
> 2 files changed, 25 insertions(+), 3 deletions(-)
>
> diff --git a/doc/filters.texi b/doc/filters.texi
> index a161754233..cfbc807f16 100644
> --- a/doc/filters.texi
> +++ b/doc/filters.texi
> @@ -21160,6 +21160,11 @@ Override default style or script info parameters of the subtitles. It accepts a
> string containing ASS style format @code{KEY=VALUE} couples separated by ",".
> @end table
>
> +@item language
> +Use first stream with the given language, ISO language code. @code{subtitles}
> +filter only. Requires the language metadata to be read from the file.
> +@end table

Using a stream specifier to select a stream would be more general.

Regards,
Marton

> +
> If the first key is not specified, it is assumed that the first value
> specifies the @option{filename}.
>
> diff --git a/libavfilter/vf_subtitles.c b/libavfilter/vf_subtitles.c
> index 82e140e986..95f0a940d9 100644
> --- a/libavfilter/vf_subtitles.c
> +++ b/libavfilter/vf_subtitles.c
> @@ -54,6 +54,7 @@ typedef struct AssContext {
>     char *fontsdir;
>     char *charenc;
>     char *force_style;
> +    char *language;
>     int stream_index;
>     int alpha;
>     uint8_t rgba_map[4];
> @@ -271,6 +272,7 @@ static const AVOption subtitles_options[] = {
>     {"stream_index", "set stream index",             OFFSET(stream_index), AV_OPT_TYPE_INT,    { .i64 = -1 }, -1,       INT_MAX,  FLAGS},
>     {"si",           "set stream index",             OFFSET(stream_index), AV_OPT_TYPE_INT,    { .i64 = -1 }, -1,       INT_MAX,  FLAGS},
>     {"force_style",  "force subtitle style",         OFFSET(force_style),  AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0, FLAGS},
> +    {"language",     "use first stream of this language", OFFSET(language), AV_OPT_TYPE_STRING, {.str = NULL}, 0, 0, FLAGS},
>     {NULL},
> };
>
> @@ -340,9 +342,8 @@ static av_cold int init_subtitles(AVFilterContext *ctx)
>         goto end;
>
>     /* Locate subtitles stream */
> -    if (ass->stream_index < 0)
> -        ret = av_find_best_stream(fmt, AVMEDIA_TYPE_SUBTITLE, -1, -1, NULL, 0);
> -    else {
> +    /* If the user has specified a particular stream use that. */
> +    if (ass->stream_index >= 0) {
>         ret = -1;
>         if (ass->stream_index < fmt->nb_streams) {
>             for (j = 0; j < fmt->nb_streams; j++) {
> @@ -357,6 +358,22 @@ static av_cold int init_subtitles(AVFilterContext *ctx)
>         }
>     }
>
> +    /* Otherwise find the first stream with the given language code. */
> +    else if (ass->language) {
> +        ret = -1;
> +        for (j = 0; j < fmt->nb_streams; j++) {
> +            const AVDictionaryEntry *lang = av_dict_get(fmt->streams[j]->metadata, "language", NULL, 0);
> +            if (lang && !strcmp(lang->value, ass->language)) {
> +                ret = j;
> +                break;
> +            }
> +        }
> +    }
> +
> +    /* Finally fall back to the "best" stream. */
> +    else
> +        ret = av_find_best_stream(fmt, AVMEDIA_TYPE_SUBTITLE, -1, -1, NULL, 0);
> +
>     if (ret < 0) {
>         av_log(ctx, AV_LOG_ERROR, "Unable to locate subtitle stream in %s\n",
>                ass->filename);
> -- 
> 2.35.1
>
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