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Can I vary bit rates in h264 mp4s?

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Paddy Uglow
Can I vary bit rates in h264 mp4s?
on Dec 14, 2009 at 5:38:41 pm

Hi,
I'm compressing hour+ long movies of talks at around 400kb/s to h264 mp4s, using QuickTime Pro on a Mac (10.5). They end up online.
The problem is that the ident at the beginning is pretty fast-moving and only looks decent at 1000+ kb/s, whereas I want the rest of the movie at around 400 kb/s. Is there a way of setting the bit rate to something high for the first 5 second, then dropping it for the rest?
I also have Premiere Pro CS3 and Final Cut Studio 2, if either of them can do it for me.
One option was to get our web player to play a short ident movie before the talk, as a separate file, but we'd ideally like it attached to the file for when people download it.
And it has to be an mp4 - I can't stick two movies together in a QuickTime movie.
Any ideas?
Thanks in advance.
- Paddy
PS: The talks are at DShed.net - they might interest film fans in the UK.


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Daniel Low
Re: Can I vary bit rates in h264 mp4s?
on Dec 14, 2009 at 7:07:12 pm

You are unlikely to get what you want from QT Pro, it's not a proper transcoder. You need to invest in Episode or compressor (which you may already have.

Using either of these, choose VBR and set a maximum datarate of 1000Kb/s and an average of 400Kb/s. After a bit of experimenting you should get the desired result.

__________________________________________________________________
"There's no chance that the iPhone is going to get any significant market share. No chance."
Steve Ballmer To USA Today: 30 April 2007


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Paddy Uglow
Re: Can I vary bit rates in h264 mp4s?
on Dec 16, 2009 at 11:07:18 am

Hi Daniel,
Thanks for the ideas. I tried Compressor but re-confirmed the reasons why I have trouble with it. Maybe it's because I've got Perian installed, but I couldn't persuade it to give me the codec I wanted. I tried some MPEG StreamClip which couldn't do what I wanted either, so I braved ffmpegx's x264 encoder settings and I think it's doing the job, with none of those "encode"...Ping! errors that I get when I'm confused with the settings.
I think it's doing variable bit-rate, with some logarithmic "quantising" value ranges. Anyway, the 3 second ident looks much better, without the file size going through the roof.
So, +1 for ffmpegx!


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Daniel Low
Re: Can I vary bit rates in h264 mp4s?
on Dec 16, 2009 at 12:11:46 pm

ffmpegX is great, but not for beginners.

__________________________________________________________________
"There's no chance that the iPhone is going to get any significant market share. No chance."
Steve Ballmer To USA Today: 30 April 2007


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