lavc/qsvdec: add query function and provide error message

It is helpful to know why some clips decoding failed.
Ticket#7330 is a good example, with this patch it is easily to
know bitstream codec level is out of support range.
Signed-off-by: Zhong Li <zhong.li@intel.com>

libavcodec/qsvdec.c

@@ -120,6 +120,33 @@ static inline unsigned int qsv_fifo_size(const AVFifoBuffer* fifo)
     return av_fifo_size(fifo) / qsv_fifo_item_size();
 }
 
+static int check_dec_param(AVCodecContext *avctx, QSVContext *q, mfxVideoParam *param_in)
+{
+    mfxVideoParam param_out = { .mfx.CodecId = param_in->mfx.CodecId };
+    mfxStatus ret;
+
+#define CHECK_MATCH(x) \
+    do { \
+      if (param_out.mfx.x != param_in->mfx.x) {   \
+          av_log(avctx, AV_LOG_WARNING, "Required "#x" %d is unsupported\n", \
+          param_in->mfx.x); \
+      } \
+    } while (0)
+
+    ret = MFXVideoDECODE_Query(q->session, param_in, &param_out);
+
+    if (ret < 0) {
+        CHECK_MATCH(CodecId);
+        CHECK_MATCH(CodecProfile);
+        CHECK_MATCH(CodecLevel);
+        CHECK_MATCH(FrameInfo.Width);
+        CHECK_MATCH(FrameInfo.Height);
+#undef CHECK_MATCH
+        return 0;
+    }
+    return 1;
+}
+
 static int qsv_decode_init(AVCodecContext *avctx, QSVContext *q)
 {
     const AVPixFmtDescriptor *desc;
@@ -206,6 +233,12 @@ static int qsv_decode_init(AVCodecContext *avctx, QSVContext *q)
     param.ExtParam    = q->ext_buffers;
     param.NumExtParam = q->nb_ext_buffers;
 
+    if (!check_dec_param(avctx, q, &param)) {
+        //Just give a warning instead of an error since it is still decodable possibly.
+        av_log(avctx, AV_LOG_WARNING,
+               "Current input bitstream is not supported by QSV decoder.\n");
+    }
+
     ret = MFXVideoDECODE_Init(q->session, &param);
     if (ret < 0)
         return ff_qsv_print_error(avctx, ret,