html video size
// width="320"
// height="240"
<video width="320" height="240" controls>
<source src="movie.mp4" type="video/mp4">
<source src="movie.ogg" type="video/ogg">
Your browser does not support the video tag.
</video>
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or Responsive
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<style>
video {
width: 100%;
height: auto;
}
</style>