Audio and video - HTML5 and CSS3 - page 141

chapters, let's use the Miro Video Converter output as a starting point
and look at some easy ways to tweak things.
If you click the FFMPEG Output button while encoding a W eb M
video, you'll see that the command being used, on Windows, is some-
thing similar to this:
ffmpeg-bin\ffmpeg.exe -y -i "C:\00092.MTS" -f webm
-vcodec libvpx -acodec libvorbis -ab 160000
-crf 22 "C:\00092.webmvp8.webm"
You can run this yourself at the command prompt. Here's a quick run-
down of what the parameters mean (don't worry too much about the
details—for the most part you won't need to change these):
❂ -y —Overwrite any existing output without prompting.
❂ -f —Container format.
❂ -acodec —Audio codec to use.
❂ -crf —Set the constant rate factor (crf). This automatically varies the
bitrate to maintain a consistent quality.
❂ -i —Input file.
❂ -vcodec —Video codec to use.
❂ -ab —Audio bitrate to use. Bigger numbers lead to larger files.
One easy change you might want to make is to change the size of the
output video, using the -s parameter. This example sets the output to
320 pixels wide by 180 pixels high:
ffmpeg-bin\ffmpeg.exe -y -i "C:\00092.MTS" -f webm
-vcodec libvpx -acodec libvorbis -ab 160000
-s 320x180 -crf 22 "C:\00092.webmvp8.320.high.webm"
It's also easy to adjust the quality of the output file by specifying a
bitrate. To do so, use the -b parameter:
ffmpeg-bin\ffmpeg.exe -y -i "C:\00092.MTS" -f webm
-vcodec libvpx -b 3600k -acodec libvorbis -ab 160000
-s 320x180 "C:\00092.webmvp8.high.webm"