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Bob Cole
test the maximum bitrate of an encoded file
on Aug 10, 2011 at 6:58:27 pm

Is there some software that I could use to test the maximum bitrate of an encoded file?

I am sending files that are encoded with Adobe Media Encoder at CBR of 300 kbps, but they are occasionally jumping to 330.

I'd like to find a way to make sure that my encodes don't exceed a given amount, so that when they are submitted to a corporate website, they don't get re-encoded (and the quality lowered) to meet their standards.

Thanks.

**EDIT** I am looking for the MAX bitrate, the jumps in bitrate, not the average over the length of the file. Thanks again.

Bob C


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Craig Seeman
Re: test the maximum bitrate of an encoded file
on Aug 10, 2011 at 8:01:11 pm

Bitrate Viewer is really good because you can see the bitrate frame by frame so you'll not only know the max but know exactly where as well.
http://www.winhoros.de/docs/bitrate-viewer/



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Bob Cole
Re: test the maximum bitrate of an encoded file
on Aug 10, 2011 at 9:41:02 pm

Thanks very much! This is a great tool. I'm using it for an .flv - hope that works.

Having seen that the peaks of my 300kbps video go all the way up to 620kbps, I'm concerned, and wonder what to do about it.

Is there any way to tell Adobe Media Encoder to clamp down on the bitrate? If I lower the target bitrate to some absurdly low figure, I might be able to get the seven or so peaks under the mandated 400kbps. But I'd rather keep the average bitrate up higher.

Advice would be most welcome!

Bob C


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Craig Seeman
Re: test the maximum bitrate of an encoded file
on Aug 10, 2011 at 9:51:44 pm

I don't have Adobe Media Encoder but some encoder have a Peak Bit Rate Constrained mode or equivalent means to designate a peak bit rate in addition to an average bit rate. This is usually found as part of Two Pass VBR encoding.



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Bob Cole
Re: test the maximum bitrate of an encoded file
on Aug 10, 2011 at 9:55:04 pm

It doesn't "never fail," but often enough... Having asked the question, I've stumbled across what I think may be the answer. Enabling two-pass encoding opens up a new set of sliders, including a maximum bitrate percentage over the average bitrate allowed.

If this works... I'll post it just in case someone else is interested. If someone else knows this won't work, I'd be curious about that.

Bob C


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Bob Cole
Re: test the maximum bitrate of an encoded file
on Aug 10, 2011 at 11:06:53 pm

Here is something odd: Bitrate Viewer shows the file to have peaks almost to 700kbps, but the client's software shows the file to be peaking under 400kbps, and therefore perfectly acceptable. Mystifying, hunh?

Bob C


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Craig Seeman
Re: test the maximum bitrate of an encoded file
on Aug 11, 2011 at 12:04:31 am

What software is your client using?
Perhaps their software measures over a set duration which may be averaging the peaks.



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Bob Cole
Re: test the maximum bitrate of an encoded file
on Aug 12, 2011 at 9:40:42 pm

You are correct.

I still have the original concern about how to make Adobe Media Encoder obey its own rules. AME creates files that, according to Bitrate Viewer anyway, have peaks double the "maximum" permitted.

Bob C


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Craig Seeman
Re: test the maximum bitrate of an encoded file
on Aug 12, 2011 at 9:51:08 pm

It's not uncommon, unfortunately, for encoders to go past their peak settings. I believe it's hard to "enforce" with certain codecs.



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Bob Cole
Re: test the maximum bitrate of an encoded file
on Aug 12, 2011 at 10:01:35 pm

I used BitRate Viewer to identify precisely where the peaks occurred. I assumed it was my "fault" -- because I had done some panning and zooming on graphics.

One of the peaks was on such a pan and zoom. But by far the majority were on simple cuts from a wide shot to a medium close-up. Not much I can do about that.

I was using Adobe Media Encoder to create .flv files. Nothing out of the encoder's comfort zone, for sure.

I'm not even sure whether this is "a problem that is a problem," or whether occasional peaks are okay. But I'd like to know. We spend so much effort trying to write good scripts, create great pictures, edit with pace, etc. -- but we (okay, I) neglect the compression area. And the viewer experience, online, can be severely compromised by jittery playback and occasional freezes.

Bob C


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Craig Seeman
Re: test the maximum bitrate of an encoded file
on Aug 12, 2011 at 10:30:42 pm

Does AME allow you to set a peak bit rate?
Is it exceeding it?
By how much?

Generally I find peaks aren't much of a problem but if someone has lower bandwidth than the peak, it's possible to get a pause while the frames buffer.



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Bob Cole
Re: test the maximum bitrate of an encoded file
on Aug 13, 2011 at 12:49:23 am

Hi Craig,

There are several sliders; here they are, with my most recent settings:

Bitrate (kbps): 300
Minimum bitrate (% target): 40
Maximum bitrate (% target): 120
Bitrate variability (% target): 80

Bitrate Viewer tells me that the actual results, for five files, expressed as average bitrates/peak, are:

309/2187
277/2191
311/1099
316/1318
280/1401

Most of the peaks are in the 600kbps range; there are usually only one or two at those highest numbers, per 20-minute program.

If you can figure out what those sliders actually mean, and how they might interact, I'm all ears!

Bob C


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