# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/(https?\:\\/\\/.+?\.webm)\h/<video width="320" height="240" controls><source src="$1" type="video\/webm"><\/video>/g;t' <<< "waka http://video.webmfiles.org/big-buck-bunny_trailer.webm wakawaka http://video.webmfiles.org/big-buck-bunny_trailer.webm wakawaka http://video.webmfiles.org/big-buck-bunny_trailer.webm wakawaka http://video.webmfiles.org/big-buck-bunny_trailer.webm wakawaka http://video.webmfiles.org/big-buck-bunny_trailer.webm wakawaka http://video.webmfiles.org/big-buck-bunny_trailer.webm wakawaka http://video.webmfiles.org/big-buck-bunny_trailer.webm wakawaka http://video.webmfiles.org/big-buck-bunny_trailer.webm waka"
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for SED, please visit: https://www.gnu.org/software/sed/manual/html_node/The-_0022s_0022-Command.html