mfenc: Fall back to avctx->time_base if avctx->framerate isn't set

The framerate field is the one users are supposed to set, but not
all users might be setting it, so it might be good to fall back
time_base in that case.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/mfenc.c

@@ -637,11 +637,19 @@ static int64_t mf_encv_output_score(AVCodecContext *avctx, IMFMediaType *type)
 static int mf_encv_output_adjust(AVCodecContext *avctx, IMFMediaType *type)
 {
     MFContext *c = avctx->priv_data;
+    AVRational framerate;
 
     ff_MFSetAttributeSize((IMFAttributes *)type, &MF_MT_FRAME_SIZE, avctx->width, avctx->height);
     IMFAttributes_SetUINT32(type, &MF_MT_INTERLACE_MODE, MFVideoInterlace_Progressive);
 
-    ff_MFSetAttributeRatio((IMFAttributes *)type, &MF_MT_FRAME_RATE, avctx->framerate.num, avctx->framerate.den);
+    if (avctx->framerate.num > 0 && avctx->framerate.den > 0) {
+        framerate = avctx->framerate;
+    } else {
+        framerate = av_inv_q(avctx->time_base);
+        framerate.den *= avctx->ticks_per_frame;
+    }
+
+    ff_MFSetAttributeRatio((IMFAttributes *)type, &MF_MT_FRAME_RATE, framerate.num, framerate.den);
 
     // (MS HEVC supports eAVEncH265VProfile_Main_420_8 only.)
     if (avctx->codec_id == AV_CODEC_ID_H264) {