oggdec: validate VP8 keyframes

Fixes seeking with broken files
Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/oggdec.c

@@ -727,8 +727,16 @@ static void ogg_validate_keyframe(AVFormatContext *s, int idx, int pstart, int p
 {
     struct ogg *ogg = s->priv_data;
     struct ogg_stream *os = ogg->streams + idx;
-    if (psize && s->streams[idx]->codec->codec_id == AV_CODEC_ID_THEORA) {
-        if (!!(os->pflags & AV_PKT_FLAG_KEY) != !(os->buf[pstart] & 0x40)) {
+    int invalid = 0;
+    if (psize) {
+        switch (s->streams[idx]->codec->codec_id) {
+        case AV_CODEC_ID_THEORA:
+            invalid = !!(os->pflags & AV_PKT_FLAG_KEY) != !(os->buf[pstart] & 0x40);
+        break;
+        case AV_CODEC_ID_VP8:
+            invalid = !!(os->pflags & AV_PKT_FLAG_KEY) != !(os->buf[pstart] & 1);
+        }
+        if (invalid) {
             os->pflags ^= AV_PKT_FLAG_KEY;
             av_log(s, AV_LOG_WARNING, "Broken file, %skeyframe not correctly marked.\n",
                    (os->pflags & AV_PKT_FLAG_KEY) ? "" : "non-");