screencast formats and online viewing research - summary

At a past meeting, I forget exactly which one to be honest, the  
question of what video format would be best to use that allows for  
online video playback while not suffering from quality issues.  I  
took a look at the common formats used by screencast tools and users  
and also at what online video sites do to mangle videos and came up  
with some notes.

First the formats - basically modern tools can capture and output in  
all of the common video formats - so that's a good thing.  Every FAQ  
and help guide I read all said the same thing, output as high of a  
resolution as you can (hmm, kinda obvious) - but the devil is in the  
details.

Because screencasts are basically a static background with a couple  
areas in motion, using a format that offers keyframes will give you  
the best compression but you will lose out on sharpness of edges.   
But this is not really noticeable unless you start messing with the  
scaling.  The one thing that is noticeable tho is audio sync issues  
and the only way to avoid that is to pick a container format (think  
mp4, flv, ogg) which has the ability to store the audio and video  
with markers to keep things lined up.  You just have to be careful in  
converting them to ensure that the output format retains the timing  
data.

One other thing to consider about format is image size.  While wide- 
screen monitors are very popular, by far 1024x768 is the most  
common.  That size for a video is almost unheard of tho in  
screencasts.  At the bottom of the email is a table I lifted from a  
great wiki page from edmug.org.uk that has tips on how to record  
using iShowU and iMovie  -- they list 640x480 as being the size to  
use if you want to show the video at 100% and be able to see the  
whole screen in the video.  (full link: http://wiki.edmug.org.uk/ 
index.php/Tutorial:Screencasts )

Most of the uploads sites do some serious compression and scaling to  
save bandwidth and screen space so they all will take a nice clean  
screen cast and mangle it so text is unreadable.  They are best used  
for shots of kittens and kids running around creating havoc.

The best option for quality, IMO, is to offer both FLV and MP4  
formats on our own site.  These two media container formats offer the  
audio/video quality and the metadata to keep them in-sync even during  
compression and/or scaling.  The FLV can be viewed in a flash viewer  
and the download option is still available.  (yep, just what Jared  
suggested originally) :)  The biggest issue for use will be bandwidth  
used.

Another benefit of MP4 that may be useful down the road is that it's  
very easy to also include in the file 3gp timed text track data -  
this will allow for captions to be included (useful for accessibility  
and also translations.)

Here are the "highlights":

Screencast formats:
	animated gif (yes, this is actually used)
		playable anywhere, 256 colors only, lossy (but good) compression,  
no sound, extremely embeddable

	ogg
		pretty much linux only, compression can be used, audio, no browser  
embed (yet)
		listed because I love the fact that it's patent-free

	h.264/mpeg4
		not widely supported by many players (tho VLC plays it and VLC is  
available everywhere), no native embed
		too bad tho - it has great quality parameters

	flv (aka flash)
		h.263 video which is widely supported, mp3 audio (but can be a  
custom codec)
		requires flash ver 8 or higher but this is available in OS X,  
Windows and Linux now

Online sites
	Youtube
		uses FLV but converted and scaled to 320x240, 30fps (max), 100meg  
max size
		best to encode as mpeg4 (divx, xvid), 320x240, mp3 audio, 30fps  
(anything else and it can be *ugly*)

	Viddler
		streaming playback only
		supports every video format under the sun (really, they are crazy  
mad with formats)
		500 meg max size
		nifty feature is they allow user comments to be recorded and they  
appear at the bottom of the video in a timeline

	Metacafe
		mpeg4 (avi, mov, mp4), 30fps, mp3 audo - no idea on max size

	Revver
		mov, mpeg, mpg, mp4, wmv, asf, avi (divx), 100meg max size
		ads are inserted into playback


Table of resolutions and video sizes borrowed from http:// 
wiki.edmug.org.uk/index.php/Tutorial:Screencasts#iShowU_Capture_Size

Type 					iMovie Resolution 	iShowU 100%	iShowU 75% 	iShowU 50%
DV PAL 					720 x 576 			720 x 576 		960 x 768 		1440 x 1152
DV NTSC 				720 x 480 			720 x 480 		960 x 640 		1440 x 960
DV-PAL 	Widescreen 		853 x 576 		853 x 576 		1138 x 768 	1706 x 1152
DV-NTSC Widescreen 	853 x 480 		853 x 480 		1138 x 640 	1706 x 960
HDV 1080i 				1920 x 1080 			1920 x 1080 		too large 		too large
HDV 720p 				1280 x 720 			1280 x 720 		1654 x 960 		too large
MPEG-4 				640 x 480 			640 x 480 		854 x 640 		1280 x 960



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