libopenh264dec: Use a newer decoding entry point function

The "new" entry point actually has existed since OpenH264 1.4 in
2015 and is the the recommended decoding entry point.

The name of this function, DecodeFrameNoDelay, is rather backwards
considering that it doesn't return the latest decoded frame immediately,
but actually does proper delaying and reordering of frames.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/libopenh264dec.c

@@ -109,10 +109,18 @@ static int svc_decode_frame(AVCodecContext *avctx, void *data,
 #endif
     } else {
         info.uiInBsTimeStamp = avpkt->pts;
+#if OPENH264_VER_AT_LEAST(1, 4)
+        // Contrary to the name, DecodeFrameNoDelay actually does buffering
+        // and reordering of frames, and is the recommended decoding entry
+        // point since 1.4. This is essential for successfully decoding
+        // B-frames.
+        state = (*s->decoder)->DecodeFrameNoDelay(s->decoder, avpkt->data, avpkt->size, ptrs, &info);
+#else
         state = (*s->decoder)->DecodeFrame2(s->decoder, avpkt->data, avpkt->size, ptrs, &info);
+#endif
     }
     if (state != dsErrorFree) {
-        av_log(avctx, AV_LOG_ERROR, "DecodeFrame2 failed\n");
+        av_log(avctx, AV_LOG_ERROR, "DecodeFrame failed\n");
         return AVERROR_UNKNOWN;
     }
     if (info.iBufferStatus != 1) {