Use the h264 parser when decoding VSSH in avi.

Fixes ticket #3261 visually.

Analyzed-by: Michael Doilnitsyn

libavformat/avidec.c

@@ -688,6 +688,8 @@ static int avi_read_header(AVFormatContext *s)
                     /* This is needed to get the pict type which is necessary
                      * for generating correct pts. */
                     st->need_parsing = AVSTREAM_PARSE_HEADERS;
+                    if (st->codec->codec_tag == MKTAG('V', 'S', 'S', 'H'))
+                        st->need_parsing = AVSTREAM_PARSE_FULL;
 
                     if (st->codec->codec_tag == 0 && st->codec->height > 0 &&
                         st->codec->extradata_size < 1U << 30) {