avformat/mux: ignore delayed vp8/9 packets in max_interleave_delta calculation

libvpx adds very significant delay, which appears normal and we must
buffer all other streams no matter what to interleave them correctly

Fixes Ticket3440
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mux.c

@@ -778,7 +778,9 @@ int ff_interleave_packet_per_dts(AVFormatContext *s, AVPacket *out,
     for (i = 0; i < s->nb_streams; i++) {
         if (s->streams[i]->last_in_packet_buffer) {
             ++stream_count;
-        } else if (s->streams[i]->codec->codec_type == AVMEDIA_TYPE_SUBTITLE) {
+        } else if (s->streams[i]->codec->codec_type != AVMEDIA_TYPE_ATTACHMENT &&
+                   s->streams[i]->codec->codec_id != AV_CODEC_ID_VP8 &&
+                   s->streams[i]->codec->codec_id != AV_CODEC_ID_VP9) {
             ++noninterleaved_count;
         }
     }
@@ -786,7 +788,11 @@ int ff_interleave_packet_per_dts(AVFormatContext *s, AVPacket *out,
     if (s->internal->nb_interleaved_streams == stream_count)
         flush = 1;
 
-    if (s->max_interleave_delta > 0 && s->packet_buffer && !flush) {
+    if (s->max_interleave_delta > 0 &&
+        s->packet_buffer &&
+        !flush &&
+        s->internal->nb_interleaved_streams == stream_count+noninterleaved_count
+    ) {
         AVPacket *top_pkt = &s->packet_buffer->pkt;
         int64_t delta_dts = INT64_MIN;
         int64_t top_dts = av_rescale_q(top_pkt->dts,