keyframe question

[seanin]

hiya,

firstly, i'm sorry if this topic has been discussed already. i looked for it here and googled it but couldn't find exactly what i was looking for...

i've been having problems with getting good video quality on youtube and i think the keyframe rate might be the problem.

my source video is:
1920x1080
25fps


if i export this to a letterboxed 480x360 quicktime movie with a h2.64 compression, what keyframe rate should i set it at? or should i just leave it at automatic...?

to be honest i don't fully understand the concept of keyframe in video (i do in animation!), so it would be great if somebody could help me out, and either explain it to me or just tell me what keyframe rate to set my 480x360 quicktime movie to with the intention of putting it on youtube. i know youtube doesn't offer the greatest video quality online and there are alternatives, but youtube is needed for this particular video.

finally, i'm led to believe from scouring forums that the data rate is linked to the keyframe rate in someway, so if this is the case advice would be much appreciated.

thanks!

[jagabo]

A keyframe in video is an entire image compressed like a JPEG file. Other frames only encode the differences between frames. Generally, the smaller the keyframe interval the more bitrate your video will require.

Since Youtube will convert whatever you upload to FLV the keyframe interval of your video won't make any difference. And since Youtube uses low bitrates you need to use techniques that are amenable to that: low noise, little motion, good and constant lighting, etc.

[seanin]

thanks very much, that's really helpful!