CEF supports WebM & Ogg Theora video codecs. MPEG-4 & H.264 are proprietary codecs and are not included in Chromium builds, as there are licensing issues:
Codecs like MP3 and AAC are included in Google Chrome releases but not Chromium builds. This is because these formats are not open and require licensing. Distributing these codecs with your application without a licensing agreement may violate the law in certain countries. You should discuss with a lawyer if appropriate.
Open html5test.com and see the Audio section. Results as of CEF v47:
audio element Yes ✔
Loop audio Yes ✔
Preload in the background Yes ✔
Web Audio API Yes ✔
Speech Recognition Prefixed ✔
Speech Synthesis Yes ✔
PCM audio support Yes ✔
AAC support No ✘
MP3 support No ✘
Ogg Vorbis support Yes ✔
Ogg Opus support Yes ✔
WebM with Vorbis support Yes ✔
WebM with Opus support Yes ✔
Open html5test.com and see the Video section. Results as of CEF v47:
video element Yes ✔
Subtitles Yes ✔
Audio track selection No ✘
Video track selection No ✘
Poster images Yes ✔
Codec detection Yes ✔
DRM support Yes ✔
Media Source extensions Yes ✔
MPEG-4 ASP support No ✘
H.264 support No ✘
Ogg Theora support Yes ✔
WebM with VP8 support Yes ✔
WebM with VP9 support Yes ✔