8.5.16

Video formats

Summary of: Video - Dive Into HTML5,  Digital Video Formats 

Video container files - AVI, MP4 etc

Video files as “AVI files” or “MP4 files” are just container formats. Just like a ZIP file can contain any sort of file within it.

A video file usually contains multiple tracks — a video track (without audio), plus one or more audio tracks (without video).

Common Container Formats

AVI (.avi): Can contain nearly any format.

Quicktime: Most often used for the locked Apple Sorenson codec.

WMV (.wmv): More or less MPEG4; can contain nearly any codec.

ASF ("Advanced Streaming Format", .asf): a subset of wmv, intended primarily for streaming: an early Microsoft implementation of an MPEG4 codec.

Codecs that are Also Containers

MPEG-1 - It is used almost exclusively for Video Compact Disks (VCD)

MPEG-2 (h.262) - It is a container format, but there is also a codec of the same name, which most people call h.262,

Video Codecs

A video codec is an algorithm by which a video stream is encoded. i.e. it specifies how to decode the video stream and displaying a series of images on the screen.

There are lossy (reduce quality) and lossless (don't reduce quality) video codecs.

H.264 - MPEG4 profiles

H.264 standard is split into “profiles,” which each define a set of optional features that trade complexity for file size.

Higher profiles use more optional features, offer better visual quality at smaller file sizes, take longer to encode, and require more CPU power to decode in real-time.

Apple’s iPhone supports Baseline profile, the AppleTV set-top box supports Baseline and Main profiles, and Adobe Flash on a desktop PC supports Baseline, Main, and High profiles.

Common Codecs

MPEG ("Moving Pictures Expert Group"): three video formats, MPEG 1, 2, and 4.

MPEG-4: A family of codecs, some of which are open, others Microsoft proprietary.

MJPEG ("Motion JPEG"): A codec consisting of a stream of JPEG images. Common in video from digital cameras, and a reasonable format for editing videos, but it doesn't compress well, so it's not good for web distribution.

DV ("Digital Video"): Usually used for video grabbed via firewire off a video camera. Fixed at 720x480 @ 29.97FPS, or 720x576 @ 25 FPS. Not very highly compressed.

WMV ("Windows Media Video"): A collection of Microsoft proprietary video codecs. Since version 7, it has used a special version of MPEG4.

DivX: in early versions, essentially an ASF (incomplete early MPEG-4) codec inside an AVI container; DivX 4 and later are a more full MPEG-4 codec.. No resolution limit. Requires more horsepower to play than mpeg1, but less than mpeg2. Hard to find mac and windows players.

Sorenson 3: Apple's proprietary codec, commonly used for distributing movie trailers (inside a quicktime container).

Quicktime 6: Apple's implementation of an MPEG4 codec.