Quick question regarding mbit/sec

A

astro21

Member
When I play footage recorded on the AF100 using the PH settings into QuickTime player 7 and look at the file info HUD, it says that the data rate is approximately 17 mbit per second when 24p. and approximately 11 mbit per second with footage I recorded in 60 frames per second using VFR. It was my understanding that when using VFR the data rate would go up to 35 mbit per second. What am I missing?
 
You're missing the relationship between how many frames were recorded in a second, and how many are played back in a second. If you recorded ten seconds of footage, the file size would be about 350 megabits. But when you go to play it back, it's not considered 10 seconds anymore, it's considered 25 seconds, because it's slow-mo, and it takes 2.5x as long to play back. But the file is still 350 megabits. So if you divide 350 megabits by 25 seconds, you get 14 megabits per second OF PLAYBACK. It was 35mbits when recorded, but because the footage is spread across the playback time, it'll look like fewer mbps for playback.

Now, I don't know why your QT player is reporting the numbers it is; on Windows every file I've examined has showed at least 21mbps for PH mode and 14mbps for 60p overcranked footage...
 
Barry, many thanks for your clear explanation.

I don't know either why the reported bit rate is lower than it should be. I am in PH mode so I have no idea.
 
Well, it also may depend on what you shoot. I haven't tried this but if you were pointing the camera at a wall, or with the lens cap on, it would probably show a lot lower bandwidth used than it would if you were pointing it at an actual scene.
 
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