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AVC/MP4 optimum bit rate value to rendering interviews…
When using AVC/MP4 (e.g. MainConcept), I am wondering if CBR would be more effective, since the rendering time is shorter (comparing to VBR two-pass) and my footage is an interview. The framing is basically the background of an office and a person behind a desk, changes in position (chair movement left/right) and hands movements.
To this context, does it make sense that CBR would be better than VBR (two-pass)?
My original footage is 1280×720, 60p, 11Mbps. Bearing in mind a equilibrium between quality and file size (and trying to avoid bps overkill), what is supposed to be a reasonable bit rate value (CBR or VBR) to be used when rendering interviews to AVC/MP4 (1280×720, 30p)?
Thanks in advance,
Cadu -
9 Replies
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Carlos, I always use the Internet 1280×720-30p preset and I think my videos look pretty good if I do say so 🙂
https://www.stclaircollege.ca/healthsciences/
https://www.stclaircollege.ca/alumni/aod-past.html -
[Carlos Silva] “My original footage is 1280×720, 60p, 11Mbps. Bearing in mind a equilibrium between quality and file size (and trying to avoid bps overkill), what is supposed to be a reasonable bit rate value (CBR or VBR) to be used when rendering interviews to AVC/MP4 (1280×720, 30p)? “
The “optimal” bit rate is the rate at which you can can no longer tell the difference. I would start with the MainConcept AVC “Internet HD 720p” template and see what you think. Increase the bit rate by 1,000,000 until you can’t see difference and then use the previous setting when you can no longer tell. I’m guessing the default template should be fine since is averages 8Mbps with peaks at 16Mbps which is higher then you original footage.
~jr
http://www.johnrofrano.com
http://www.vasst.com -
Thanks everybody for answering! The MainConcept Internet 720p preset seems to be the way to go indeed. And by testing variations of 1,000,000 I think I will achieve best file size x quality.
Anyway, considering this preset and my original footage characteristics, there are a couple of points I am a little bit confused:
a) In this preset the average (bps) is 8Mbps and maximum is set to 16Mbps. But since my original footage is 11Mbps, it seems I could set the maximum bit rate to 11Mbps to avoid a supposed overkill of the preset working unnecessarily at 16Mbps. Does it make sense?
b) My original footage is 1280×720, 60p, 11Mbps.
When rendering, I am maintaining same resolution (1280×720), but downsizing the fps to 30p. Let’s suppose I use CBR to try achieving an optimum quality as close as possible to my original footage. Since the fps are half of the original footage, it seems logical that I could downsize the bit rate to 5.5Mbps without quality loss. In other words, using the same 11Mbps would be overkill since I am using half of the fps when rendering. Does it make sense?Cheers,
Cadu -
the process doesn’t analyze your video’s bps. what it analyzes are its pixels. the higher the output bitrate, the final quality gets better.
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[Carlos Silva] “a) In this preset the average (bps) is 8Mbps and maximum is set to 16Mbps. But since my original footage is 11Mbps, it seems I could set the maximum bit rate to 11Mbps to avoid a supposed overkill of the preset working unnecessarily at 16Mbps. Does it make sense? “
Yes this makes sense and I’m sorry I didn’t suggest this. 11Mbps max would be fine for your footage.
[Carlos Silva] “b) My original footage is 1280×720, 60p, 11Mbps. When rendering, I am maintaining same resolution (1280×720), but downsizing the fps to 30p. Let’s suppose I use CBR to try achieving an optimum quality as close as possible to my original footage. Since the fps are half of the original footage, it seems logical that I could downsize the bit rate to 5.5Mbps without quality loss. In other words, using the same 11Mbps would be overkill since I am using half of the fps when rendering. Does it make sense?”
Once again your thinking is correct. 1/2 the frames requires 1/2 the bit rate. Using a Max of 11Mbps and an average of 5.5Mbps should work well. I would not change the 11Mbp. If it’s not needed it will never be used. It’s just a maximum setting that’;s allowable “if needed” and won’t hurt anything.
~jr
http://www.johnrofrano.com
http://www.vasst.com -
I am not sure this is correct. Bitrate is important. Pixels decide the square bits in the video. Bitrate decides the compression applied and thus the “smearing” that occurs due to compression, of colours and detail.
Sorry if I misunderstand.
Nick
Head: Hertz Music -
what i meant to say was:
it is unimportant what is the bitrate of the input file.
what encoding does is taking frames, analyzing its pixels, applying compression algorithms and outputting the encoded frames regardless the input bitrate.
so i don’t think that saying “my input file is 1 mbps, so it is useless to apply 2 mbps on the output for reencoding” is correct.
of course there are boundaries above which it is useless to apply certain level of bitrate to a file. i am thinking: aplying 2 mbps to 1 mbps file would produce better results then applying 1 mbps to 1 mbps file. while applaying 50 mbps to 25 mbps file, i think will not make visual difference compering to applying 25 mbps to the same file. naturally resolution and output format have huge importance here too.
i hope it is clear enough. but i am not an expert, we have few here, i will be pleased to learn from them. -
Thanks everybody for the fruitful clarifications!
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To tackle your original question of VBR vs CBR, that would depend on what you think of as optimal. If you mean optimal quality, then CBR is probabl;y going to be better if you don’t care about file size. If you are concerned about file size, then especialy with a talking head on a static bland background, VBR will be VERY efficient file size wise. If you mean optimal encoding time wise, then obviously CBR is much quicker than 2-pass Vbr.
I will typically use CBR if I am doing a test viewing on my TV or something and then 2-pass VBR if the final render is being uploaded or burned to keep file size down.
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