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spackler787
Currently Being Moderated

Low bitrate confusion

Jan 25, 2013 6:28 PM

I have a question about bitrate that I'd love some help with...

 

My source video is 1080p using a Canon 6D. In Premier Pro CS5 my project sequences are set to HDV 720p30, as I intend to export at 720p.

 

My export settings are:

NTST, 1280x720, 29.97fps, Progressive AAC 320kbps, 44.1 hKz, Stero

VBR, 2Pass, Target 6Mbps, Max 8 Mbps.

Square Pixels, Baseline Profile, Level 3.2

 

Everytime I render my movie, the resuting mp4 shows a bit rate of about 3200 kbps. Even if I select CBR / 6 Mbps I still get roughly 3000 kbps out.

 

Why so low? Wouldn't you expect something between the Target and the Max bitrate? My "movie" content is a video of someone drawing a picture, so a lot of frames are blank white-paper until the drawing progresses - so I guess there is a lot of potential for compression, but still seems really low.

 

Should I be using 1080 for my sequences and exporting at 720 instead? The source files at 1080p are showing a bitrate of approximatley 31,470 kbps.

 

Thanks for any pointers!

Cheers,

-Brett

 
Replies
  • Currently Being Moderated
    Jan 26, 2013 8:50 AM   in reply to spackler787

    mp4 shows a bit rate of about 3200 kbps.

     

    How exactly do you determine that?

     
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    Jan 26, 2013 8:58 AM   in reply to spackler787

    Just for grins, I set up 1080i HDV in a 720p sequence. I trimmed the clip to 10 seconds and exported six times.

     

    Each time I used VBR 2 pass, 6 to 8Mbps. The first three I used level 3.2 and the second three I used 4.2

     

    For each level I used baseline, main and high. I chose a clip without much movement. I was just getting the camera set up, but it seemed like using a low motion video was appropriate for this example.

     

     

    The results surprised me a bit. The file sizes ranged from 7587K (four of the files) and there was one at 7569K and one at 7571K.

     

    According to MediaInfo, the bitrate remained pretty constant at 6007Kbps (four of them) and 5993K, 5992K. The low end of the scale, but not surprising for a low motion video on a tripod.

     

    Unfortunately, my eyes are not good enough to tell the difference in the quality of the clips either. I would have thought it would be more obvious. I guess I need to research profiles and levels. I can tell you that when I tried to move up to 4.2 the software decided I needed to be using 1080p so I had to manually change the frame size again.

     

    Just to make sure that the blank white frames were not the issue, I added 10 seconds of a white color matte. This time the High, 4.2 came out to almost exactly twice the file size and MediaInfo says it is 6022Kbps. Why it is a higher bit rate is a mystery to me, but one I will have to figure out at a later date unless we can get someone like Kevin to pitch in and straighten me out.

     

    So, Brett, there is no reason that I can see that your bitrate should be that low. Which leads me to ask how you are measuring it? Can you post a screen grab of the export settings?

     
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  • Currently Being Moderated
    Jan 26, 2013 10:57 AM   in reply to spackler787

    OK, stepping back a bit, I would ignore the intended Export, and use that footage in a Sequence, that matches the footage 100%. That is the best start. Then, when done, choose the intended Export attributes.

     

    That does not directly address the question (Steven is doing a good job of that), but will yield a better workflow for you.

     

    Good luck,

     

    Hunt

     
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  • Currently Being Moderated
    Jan 26, 2013 1:35 PM   in reply to spackler787

    The bitrate is stamped in the EXIF info of the mpg file, I assume.

     

    That is not the most accurate way to see a file's bitrate.

     

    Open it up in VLC.  In the menu, go to Tools>Codec Information.  Switch to the Statistics tab and you'll see Content bitrate.  This will show you realtime what the bitrate actually is at any moment of the video.

     
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  • Currently Being Moderated
    Jan 26, 2013 4:54 PM   in reply to spackler787

    If one is using multi-pass Encoding, then fluctuations in Bit-Rate should occur. Sections with more motion, and especially off-axis motion, should have a higher Bit-Rate than more static sections. That is what multi-pass is designed to do, and one reason that Hollywood uses Encoders, that might sample 20 passes. They want both the highest quality, but with the lowest disc overhead. To get that, Hollywood spends $ 100,000's, and hire people, who are experts, plus do nothing all day, BUT Encode to disc.

     

    One-pass does just that - uses what you set, and sticks to it. Multi-pass samples the full Video, and does its best to get high motion material at a higher Bit-Rate, and static at lower Bit-Rate.

     

    Hunt

     
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  • Currently Being Moderated
    Jan 26, 2013 5:42 PM   in reply to Bill Hunt

    OK, I understand what everyone is saying, however, I still have a question.

     

    Why does his say 3822 and mine says 6203? I get a little difference, but not that much.

     

    Also, while I agree that editing in 1080 makes more sense most of the time, I often edit in 720 if the scene was far away and I need some digital zoom, so to speak, without losing quality. Heck, I have edited in 640X480 to zoom way in on something very far away, rather than actually use Motion to make it bigger.

     

    Capture.JPG

     

    Anyway, I suggest that posting a screen shot of the export settings would be the next best step.

     
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  • Currently Being Moderated
    Jan 26, 2013 8:02 PM   in reply to spackler787

    So ignore the Vimeo warning and carry on?

     

    Honestly, just use a Vimeo preset and you should not get any warnings.

     
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  • Currently Being Moderated
    Jan 27, 2013 7:50 AM   in reply to Bill Hunt

    That is what multi-pass is designed to do

    One-pass does just that - uses what you set, and sticks to it.

     

    That's inaccurate.  One or two passes doesn't define whether or not the bitrates fluctuate.  With anything but CBR, the bitrates fluctuate based on the content.  The point and purpose of two passes is to simply to do the job better.  One pass to analyze and one to encode, instead of all at once.

     

    It's like shooting a play you've never seen (one pass) or seeing it first and then shooting it (two pass).  With the latter scenario, you have a much better idea of what's coming up and where you should be pointing the camera.  With two pass VBR, the encoder has a better idea of what's coming up and where best to use the available bits.

     

    Having said that, in my experience there is little or no visible difference between one and two passes.  More often than not, all you get with two pass is a longer coffee break.

     
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  • Currently Being Moderated
    Jan 26, 2013 11:07 PM   in reply to spackler787

    There are some things in your export settings that are not in mine.

     

    First of all, I don't use the MainConceot H.264 codec, so maybe that is why your settings indicate NTSC where mine do not. In fact, using a codec that did not come with Premiere Pro eliminates a lot of comparisons. Perhaps someone with MainConcept can assist you further.

     

    By the way, if you change to the YouTube settings, the bit rate goes up to 8Mb/s, but you can lower or raise it if you wish.

     
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  • Currently Being Moderated
    Jan 26, 2013 11:40 PM   in reply to spackler787

    Even when you pick the YouTube preset?

     
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  • Currently Being Moderated
    Jan 26, 2013 11:45 PM   in reply to spackler787

    Oh, sorry, I skipped CS4 and CS5 and came back with CS6.  Perhaps someone else can assist.

     
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  • Currently Being Moderated
    Jan 27, 2013 7:53 AM   in reply to spackler787

    with the Vimeo HD preset, I find I get Lip-sync issues.

     

    That's not normal.  Can you post a link to an example, or maybe upload a clip?

     

    https://www.depositfiles.com/en/

     
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