To support multiple browsers, you'll need to use FFmpeg to convert your.mov
file to two different containers: an MP4 container and a WebM container. In
actual practice, you would likely specify a codec at the same time. For now,
we're letting FFmpeg use its defaults.
If these concepts are new to you, you should read Media file basics before going further. Additionally, if you don't have FFmpeg installed read Media application basics to get it set up with Docker.
We are using the suggested Docker install and
theglocken.movfile fromPrepare media files for the web
added inside themediadirectory. We used FFmpeg version 4.3.2 for all the
commands in this section.
Containers
First, we need to create our two containers from the.movfile with the.mp4
and.webmfile extensions with both an audio and video stream inside the file.
ReviewMedia file basics
for more about containers and streams if you don't know the different between
them.
MP4
/media # ffmpeg -i glocken.mov glocken.mp4WebM
/media # ffmpeg -i glocken.mov glocken.webm
WebM takes longer to create than MP4. This isn't surprising when you look at
the results. While MP4 compresses to about83%of the original file's
size, WebM is down to78%of the original's size, but can be much smaller.
Your results will vary. It's important to call out that FFmpeg4.2.2set the
default video bitrate to200kand in4.3.2it does not set a default bitrate.
So the video is no longera mere4%of the original.You can see this for yourself
using thels -abash commandin the folder where your media files are located.
For example:
/media # ls -l
-rw-r--r-- 1 root root 12080306 Mar 7 12:16 glocken.mov
-rwx------ 1 root root 10106446 Mar 7 12:33 glocken.mp4
-rwx------ 1 root root 9503301 Mar 7 18:30 glocken.webm
To get a tiny file, you would do this instead:
/media # ffmpeg -i glocken.mov -b:v 200k glocken.webm
...
frame= 300 fps=3.6 q=0.0 Lsize= 483kB time=00:00:10.01 bitrate= 395.0kbits/s speed=0.121x
video:359kB audio:117kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 1.356068%
/media # ls -l
-rw-r--r-- 1 root root 12080306 Mar 7 12:16 glocken.mov
-rwx------ 1 root root 10106446 Mar 7 12:33 glocken.mp4
-rwx------ 1 root root 494497 Mar 7 18:45 glocken.webm
Check your work
To verify your results, use FFmpeg and Shaka Packager as already shown in Media Application basics:
/media # packager input=glocken.mp4 --dump_stream_info
/media # ffmpeg -i glocken.mp4
Codecs
Next, the codec. As stated inMedia file basics,a codec
isnotthe same thing as a container (file type). Two files of the same container
type could hold data compressed using different codecs. The WebM format for example
allows audio to be encoded using eitherVorbisorOpus.To change the codec we
use FFmpeg. For example, this command outputs an.mkvfile with avorbisaudio
codec and anav1video codec.
/media # ffmpeg -i glocken.mov -c:a vorbis -c:v av1 glocken.mkv
In this example, the-c:aflag and the-c:vare for specifying the audio and
video codecs respectively.
TheMedia conversionpage lists commands needed to convert codecs. The tables below summarize the libraries used in FFmpeg to perform the codec conversions for WebM and MP4 files. These are the formats recommended for DASH and HLS respectively.
Video
| Codec | Extension | Library |
|---|---|---|
| av1 | WebM, mkv | libaom-av1 |
| h264 | MP4 | libx264 |
| vp9 | WebM | libvpx-vp9 |
Audio
| Codec | Extension | Library |
|---|---|---|
| aac | MP4 | aac |
| opus | WebM | libopus |
| vorbis | WebM | libvorbis |
Next, we'll show you how to change thebitrateof your newly created files.