[FFmpeg-devel] [PATCH 2/2] Use private option to specify WebVTT kind

[Matthew Heaney]

WebVTT subtitle tracks have four kinds. Certain downstream muxers
(such as for WebM) need to know which WebVTT kind this is, in order to
specify the codec id of the output track.

A new private input option, "-kind", has been added to the WebVTT
demuxer.  It accepts as a value any of "subtitles" (the default),
"captions", "descriptions", and "metadata".  The kind option value is
used to assign a value to the stream disposition flag, to which four
new values have been added, corresponding the four WebVTT kinds.
---
 libavformat/webvttdec.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/libavformat/webvttdec.c b/libavformat/webvttdec.c
index 7d9910b..cae5243 100644
--- a/libavformat/webvttdec.c
+++ b/libavformat/webvttdec.c
@@ -29,9 +29,12 @@
 #include "subtitles.h"
 #include "libavutil/bprint.h"
 #include "libavutil/intreadwrite.h"
+#include "libavutil/opt.h"
 
 typedef struct {
+    const AVClass *class;
     FFDemuxSubtitlesQueue q;
+    int64_t kind;
 } WebVTTContext;
 
 static int webvtt_probe(AVProbeData *p)
@@ -66,6 +69,7 @@ static int webvtt_read_header(AVFormatContext *s)
     avpriv_set_pts_info(st, 64, 1, 1000);
     st->codec->codec_type = AVMEDIA_TYPE_SUBTITLE;
     st->codec->codec_id   = AV_CODEC_ID_WEBVTT;
+    st->disposition |= webvtt->kind;
 
     av_bprint_init(&header, 0, AV_BPRINT_SIZE_UNLIMITED);
     av_bprint_init(&cue,    0, AV_BPRINT_SIZE_UNLIMITED);
@@ -186,6 +190,35 @@ static int webvtt_read_close(AVFormatContext *s)
     return 0;
 }
 
+#define OFFSET(x) offsetof(WebVTTContext, x)
+#define KIND_FLAGS AV_OPT_FLAG_SUBTITLE_PARAM
+
+static const AVOption options[] = {
+    { "kind", "Kind of WebVTT track",
+      OFFSET(kind), AV_OPT_TYPE_INT, { .i64 = 0 },
+      0, INT_MAX, KIND_FLAGS, "WEBVTT_KIND" },
+    { "subtitles", "WebVTT subtitles kind",
+      0, AV_OPT_TYPE_CONST, { .i64 = 0 },
+      INT_MIN, INT_MAX, 0, "WEBVTT_KIND" },
+    { "captions", "WebVTT captions kind",
+      0, AV_OPT_TYPE_CONST, { .i64 = AV_DISPOSITION_CAPTIONS },
+      INT_MIN, INT_MAX, 0, "WEBVTT_KIND" },
+    { "descriptions", "WebVTT descriptions kind",
+      0, AV_OPT_TYPE_CONST, { .i64 = AV_DISPOSITION_DESCRIPTIONS },
+      INT_MIN, INT_MAX, 0, "WEBVTT_KIND" },
+    { "metadata", "WebVTT metadata kind",
+      0, AV_OPT_TYPE_CONST, { .i64 = AV_DISPOSITION_METADATA },
+      INT_MIN, INT_MAX, 0, "WEBVTT_KIND" },
+    { NULL }
+};
+
+static const AVClass webvtt_demuxer_class = {
+    .class_name  = "WebVTT demuxer",
+    .item_name   = av_default_item_name,
+    .option      = options,
+    .version     = LIBAVUTIL_VERSION_INT,
+};
+
 AVInputFormat ff_webvtt_demuxer = {
     .name           = "webvtt",
     .long_name      = NULL_IF_CONFIG_SMALL("WebVTT subtitle"),
@@ -196,4 +229,5 @@ AVInputFormat ff_webvtt_demuxer = {
     .read_seek2     = webvtt_read_seek,
     .read_close     = webvtt_read_close,
     .extensions     = "vtt",
+    .priv_class     = &webvtt_demuxer_class,
 };
-- 
1.8.3