imovie mpeg-4 settings

[plunar]

is there any advantage/disadvantage to not checking "enable streaming" under the mp4 settings in imovie?

i noticed when i checked it my movie came out twice the size expected....bigger than the same movie at double the bit-rate.....


also, does the "optimized for:" pull down menu have any real effect??? thanks

 

[freiheit]

Keyframes

I suspect (not 100% sure) that the Enable Streaming option probably puts a lot more keyframes into the movie. Adding keyframes makes the movie seekable but more importantly for streaming, it allows someone to come into the stream almost instantaneously rather than having to wait a couple of seconds for the next keyframe to come by. The problem with keyframes is they are typically complete frames -- where frames between keyframes are usually just stored as the difference between the last frame and the next which allows them to be compressed more. Keyframes don't compress as well and so the size of your video goes up with the streaming option enabled.