webm (vp9/opus) stuttering on mobile

[machenotizia]

Hi from Italy;
i'm making several tests with vp9. I want to understand if i can use vp9 istead of h.264 to improve quality/bitrate of my videos online.
i have some problems.
Firefox and Chrome (desktop windows) can playback without problems WebM(vp9/opus) videos.
Chrome on Nexus 4 , Samsung Galaxy S3, Nexus7, with Kitkat or Lollipop, has stuttering problems. There is not a bandwith problem because videos are server by local web server.
I tried with several encoders and several parameters (changing profile from 0 to 3) but nothing changes.
so, with youtube-dl i downloaded some youtube videos, and those videos works well, but has no audio track (?).
i tried to understand what are differences about my videos and youtube videos by mediainfo, but i'm not able to understand what change.


this is a sample use of encvpx.exe script called by "Hybrid" encoder gui. Hybrid is the name of the software.

vpxenc --codec=vp9 --passes=1 --pass=1 --target-bitrate=1500 --end-usage=vbr --good --cpu-used=3 --undershoot-pct=0 --buf-sz=6 --buf-initial-sz=4 --buf-optimal-sz=5 --drop-frame=0 --resize-allowed=0 --kf-min-dist=0 --kf-max-dist=250 --auto-alt-ref=0 --noise-sensitivity=0 --sharpness=0 --static-thresh=0 --tile-columns=2 --tile-rows=2 --threads=8 --width=1280 --height=720 --yv12 -o "C:\Juassikvp9.vp9" -

i tried also with mediaCoder, but nothing changed.

any suggestions to avoid stuttering problem? How youtube encode vp9 avoiding stuttering problems?

thanks.