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FLV File Dimensions Don't Effect File Size or Quality?

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Dave Averdick
FLV File Dimensions Don't Effect File Size or Quality?
on May 28, 2010 at 6:54:02 pm

So I am trying to determine the optimal bitrate and file dimensions for creating FLVs and I am surprised about my results so far, maybe someone can shed some light on this issue. I have encoded 3 FLVs, all of which use the same bitrate of 8,000 kbps. The first FLV used full HD 1920 x 1080, the second 1280 x 720, and the third 720 x 405. All of them have almost the exact same quality and the file size only varied slightly, i'm talking half a megabyte difference between the full HD version and the 720 x 405 flv. So I am very surprised the FLVs dimensions don't affect the file size or quality. Does anyone know why this would be? Are these files completely dependent upon the bitrate? Seems odd to me, seems like the bitrate would be just as crucial as the files dimensions.

FLV Codec: Sorenson Spark
FLV Bitrate(CBR): 8000 KBPS
FPS: 29.97

Thanks!
Dave Averdick
http://www.daveaverdick.com


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Mike Smith
Re: FLV File Dimensions Don't Effect File Size or Quality?
on May 30, 2010 at 10:22:15 am

That's a very high bit rate. As you cut the bitrate you may notice more variation in quality.


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Dave Averdick
Re: FLV File Dimensions Don't Effect File Size or Quality?
on Jun 1, 2010 at 1:55:55 pm

The bitrate is high, but these videos are for a digital signage system, so they need to be flawless. I am surprised that the file size was literally almost the exact same between the full HD video and the much smaller 720 x 405 video. If I create a Quicktime video with the same bitrate but different dimensions the size of the .mov will be much different. The only difference with the FLV, that I have noticed is that the playback speed of the full HD FLV is skipping frames on a slow PC compared to the 720 x 405 FLV which will play fine. Anyway, I just found the results of my testing bitrate and dimension combinations for FLVs to be curious and didn't know if their was an explanation.

Thanks,
Dave


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Mike Smith
Re: FLV File Dimensions Don't Effect File Size or Quality?
on Jun 1, 2010 at 5:30:24 pm

Well, you would expect a specific bitrate to give a specific file size, wouldn't you, so long as the source video has enough data in it to fill the bit rate ..? Bitrate means so many bits per second ... so you should, roughly get so many bits per second. If you have a bigger picture, then your data is spread over a bigger pixel grid, and you may see more compression artefacts ... but if your data rate is high enough that your compression looks clean even on big screen sizes, great.

I wonder, though, whether Flash is a great choice for digital signage. Does the Flash player give you as clean, smooth and dependable result as, say, the QT player or the Windows Media Player?


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Dave Averdick
Re: FLV File Dimensions Don't Effect File Size or Quality?
on Jun 1, 2010 at 6:12:53 pm

Okay, that makes sense, I was making the assumption that the file size/quality was based on the files dimensions & bitrate, not bitrate alone. And yes, a different format would be preferable, but sadly the system is very limited in video capabilities and FLV is the only option. The reason is that most of our files are .swfs, which are great for creating quick ads that can accept data, such as xml.

Thanks for the clarifying that for me.
:D

-Dave


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