[FFmpeg-devel] [PATCH] WebVTT demuxer - save cue id and settings as side data

[Matthew Heaney]

Currently the WebVTT demuxer parses the cues but throws away
the cue id (the optional first line of the cue) and cue
settings (the optional rendering instructions that follow
the timestamp).

However, in order to write inband text tracks (to WebM
files), the entire cue payload from the WebVTT source must
be preserved.

This change makes no change to the data part of the output
buffer packet (where the actual cue text is stored), but
does add the cue id and settings as a single new side data
item.  Existing code that cares only about the data part of
the packet can continue to ignore the side data.
---
 libavformat/webvttdec.c | 32 ++++++++++++++++++++++----------
 1 file changed, 22 insertions(+), 10 deletions(-)

diff --git a/libavformat/webvttdec.c b/libavformat/webvttdec.c
index 694a020..a169d11 100644
--- a/libavformat/webvttdec.c
+++ b/libavformat/webvttdec.c
@@ -74,8 +74,9 @@ static int webvtt_read_header(AVFormatContext *s)
         int i;
         int64_t pos;
         AVPacket *sub;
-        const char *p, *identifier;
-        //const char *settings = NULL;
+        const char *p, *identifier, *settings;
+        int len, identifier_len, settings_len;
+        uint8_t* buf;
         int64_t ts_start, ts_end;
 
         ff_subtitles_read_chunk(s->pb, &cue);
@@ -92,15 +93,15 @@ static int webvtt_read_header(AVFormatContext *s)
             continue;
 
         /* optional cue identifier (can be a number like in SRT or some kind of
-         * chaptering id), silently skip it */
+         * chaptering id) */
         for (i = 0; p[i] && p[i] != '\n'; i++) {
             if (!strncmp(p + i, "-->", 3)) {
                 identifier = NULL;
                 break;
             }
         }
-        if (identifier)
-            p += strcspn(p, "\n");
+        identifier_len = identifier ? strcspn(p, "\n") : 0;
+        p += identifier_len;
 
         /* cue timestamps */
         if ((ts_start = read_ts(p)) == AV_NOPTS_VALUE)
@@ -112,16 +113,18 @@ static int webvtt_read_header(AVFormatContext *s)
         if ((ts_end = read_ts(p)) == AV_NOPTS_VALUE)
             break;
 
-        /* optional cue settings, TODO: store in side_data */
+        /* optional cue settings */
         p += strcspn(p, "\n\t ");
         while (*p == '\t' || *p == ' ')
             p++;
+        settings = p;
+        settings_len = strcspn(p, "\n");
+        p += settings_len;
         if (*p != '\n') {
-            //settings = p;
-            p += strcspn(p, "\n");
+            av_log(s, AV_LOG_ERROR, "Bad WebVTT cue.\n");
+            return AVERROR(EINVAL);
         }
-        if (*p == '\n')
-            p++;
+        p++;
 
         /* create packet */
         sub = ff_subtitles_queue_insert(&webvtt->q, p, strlen(p), 0);
@@ -132,6 +135,15 @@ static int webvtt_read_header(AVFormatContext *s)
         sub->pos = pos;
         sub->pts = ts_start;
         sub->duration = ts_end - ts_start;
+
+        len = identifier_len + 1 + settings_len + 1;
+        buf = av_packet_new_side_data(sub, AV_PKT_DATA_NEW_EXTRADATA, len);
+        memcpy(buf, identifier, identifier_len);
+        buf += identifier_len;
+        *buf++ = '\n';
+        memcpy(buf, settings, settings_len);
+        buf += settings_len;
+        *buf++ = '\n';
     }
 
     ff_subtitles_queue_finalize(&webvtt->q);
-- 
1.8.2.1