lavf/webvttdec: save cue id and settings as side data

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 commit 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 side data items, if
they're present in the cue. Existing code that cares only
about the data part of the packet can continue to ignore the
side data.

There are two new packet data type flags,
AV_PKT_DATA_WEBVTT_IDENTIFIER and
AV_PKT_DATA_WEBVTT_SETTINGS.

1 files changed, 11 insertions, 0 deletions

diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index 93d63e8873..5ece48ce29 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -1008,6 +1008,17 @@ enum AVPacketSideDataType {
      * by data.
      */
     AV_PKT_DATA_MATROSKA_BLOCKADDITIONAL,
+
+    /**
+     * The optional first identifier line of a WebVTT cue.
+     */
+    AV_PKT_DATA_WEBVTT_IDENTIFIER,
+
+    /**
+     * The optional settings (rendering instructions) that immediately
+     * follow the timestamp specifier of a WebVTT cue.
+     */
+    AV_PKT_DATA_WEBVTT_SETTINGS,
 };
 
 /**