This is normal. The traffic initially bursts to fill the client buffer, then settles down for the duration.
Similar thread linked below. The problem, in that thread, is that the movie is poorly encoded and/or multiplexed.
You can try re-muxing the file to see if that helps. If it does not, try re-encoding it. Remuxing is a lot like “save as” in a word processor, etc. It makes a copy of the file, hopefully correcting any errors along the way. It is fast and should take just a few minutes to complete. Re-encoding is creating a new file from the original source (if you have it). It may take hours depending on the source material and the speed of the system where you are transcoding (hence, the suggestion to try remuxing first).
MKVToolNix: Can take MP4 as input. Output is MKV only. Use Multiplexer tab.
XMediaRecode: Can remux (copy) and re-encode. Works will multiple containers, including MP4 & MKV.
Subler: Mac only. MKV/MP4 input. MP4 output. Very good muxing tool. Can also download metadata (cover art, actors, etc) from online sources.
Handbrake: Transcoding/encoding tool. No remux capability.
With any tool and output is MP4 container, be sure and optimize the file. It will show up as Optimize, MP4 FastStart, or similar. This moves some bits around in the MP4 header so the client buffers less information and streaming begins sooner. Google “MP4 Fast Start” for more info.
