Access detailed configuration for the x264vfw - H.264/MPEG-4 codec in Export Animation> Resolution tab> Codec. Change to x264vfw codec then click Configure. 

Use the following settings to achieve desired results or adjust per your need:

• Zero Latency makes video creation smooth but might slightly increase export time. 

• Virtual Dub Hack prevents loosing some frames, especially at the beginning of the video (it happens sometimes, when video is not buffered properly before encoding, on computers with a slower graphics cards).

• Set Rate Control to Single pass / lossless to ensure but the best quality of encoding but file size is slightly larger. 

Example settings from user 1:

Example settings from user 2: