18 Replies Latest reply: Apr 24, 2014 11:09 AM by Ryan06 RSS

    Media Encoder creates lower bitrate H.264 than I select?

    chuck farris Community Member

      Hello All,

      I'm new to Adobe (an Avid transplant- I will probably be seeking waaaay too much assistance, please bear with me, I search when possible...).

       

      My first problem- I'm trying to make a 1080 H.264- I set Target bitrate to 8.5, Max to 9.

       

      This results in a H.264 at about a 2.5 bitrate, and a file less than half the size expected.

       

      The original is 1920x1080 AVCHD, I'm using 2-pass VBR, what am I doing wrong?

      thanks!

        • 1. Re: Media Encoder creates lower bitrate H.264 than I select?
          JSS1138 CommunityMVP

          How are you determining the bitrate of the export?

          • 2. Re: Media Encoder creates lower bitrate H.264 than I select?
            chuck farris Community Member

            By using the sliders under Bitrate Settings- is there another way? Thanks.

            • 3. Re: Media Encoder creates lower bitrate H.264 than I select?
              JSS1138 CommunityMVP

              No, not the settings for export, the actual bitrate of the exported file?  How do you know it's 2.5?

              • 4. Re: Media Encoder creates lower bitrate H.264 than I select?
                Colin Brougham Community Member

                The original is 1920x1080 AVCHD, I'm using 2-pass VBR, what am I doing wrong?

                 

                Nothing. VBR means "variable bit rate" and when you set the target and maximum bit rates, those are just limits to the encoder. If the encoder doesn't need all those bits, it doesn't use them--that's what makes H.264 particularly efficient. If you want a specific file size, you can use CBR or "constant bit rate." You probably won't see a major quality increase, but you will see a file size increase.

                • 5. Re: Media Encoder creates lower bitrate H.264 than I select?
                  chuck farris Community Member

                  Ah, sorry - I use Media Info, very accurate on rates, codecs used, etc.

                   

                  Plus, as I said before, the file sizes are 1/2 to 1/3 the size of similar length videos  previously encoded in Sorensonat the same bitrate.

                  • 6. Re: Media Encoder creates lower bitrate H.264 than I select?
                    JSS1138 CommunityMVP

                    If the encoder doesn't need all those bits, it doesn't use them

                     

                    It actually does with VBR, which doesn't quite mean what many people think it means.

                     

                    When you set a Target bitrate, the encoder will work to meet that target, even to the point of adding unnecessary bits.  You can test this by exporting out two segments of the same duration with the exact same export settings; one a piece of video, the other a pure black screen.  While the black should require very few bits and should come out much, much smaller, you will find only a small difference in file size.

                     

                    The only way to use "only the necessary bits" is to use CQ mode (Constant Quantization, a.k.a. Constant Quality) which the included MainConcept encoder does not offer.  With CQ mode, you specify a quality level, not a bitrate, and the encoder uses whatever bits it needs to meet that level of quality.

                     

                    That's why I use external encoders which do offer that option.

                     

                    http://tangentsoft.net/video/mpeg/enc-modes.html

                     

                    (Disclaimer:  This was all tested with MPEG2 for DVD.  But as H.264 also offers a CQ mode with the right encoder, the assumption is the same would apply.)

                    • 7. Re: Media Encoder creates lower bitrate H.264 than I select?
                      JSS1138 CommunityMVP

                      I use Media Info, very accurate on rates, codecs used, etc.

                       

                      Ah.

                       

                      I've found it to be less than accurate on occasion.  Personally, I'd not worry about it.

                      • 8. Re: Media Encoder creates lower bitrate H.264 than I select?
                        chuck farris Community Member

                        I also use Get Info (I'm on a Mac).

                         

                        Regarding VBR, seems you guys disagree, but it's my understanding that if the material's complexity (motion, detail, etc) warrants, the bitrate goes up, if not, it stays lower. Isn't this the case? Thanks.

                        • 9. Re: Media Encoder creates lower bitrate H.264 than I select?
                          JSS1138 CommunityMVP

                          Yes, but only to a degree using VBR.  To get that 'feature' in it's entirety, you need to use CQ mode.

                          • 10. Re: Media Encoder creates lower bitrate H.264 than I select?
                            chuck farris Community Member

                            So for quality for rate/size would you rate them:
                            1 CQ

                            2 VBR

                            3 CBR?

                             

                            Also, as long as you're being so generous with your time, what's Profile and Level in Encoder? Where should they be set?

                             

                            And I assume for Pixel Aspect Ratio, I should be using Square Pixels, not Widescreen 16:9?
                            (If so, when would you use WS 16:9?)

                             

                            Thanks

                            • 11. Re: Media Encoder creates lower bitrate H.264 than I select?
                              Colin Brougham Community Member

                              That's not the case with H.264, which is a much more advanced codec than MPEG2. If it doesn't need all of the allotted bits in VBR to encode a frame/GOP, it won't use them. When it needs them, it does; that's why it's important to use 2-pass VBR.

                               

                              2-pass VBR will always trump CQ for quality and usually size; CQ is just faster and usually gives good enough results.

                              • 12. Re: Media Encoder creates lower bitrate H.264 than I select?
                                chuck farris Community Member

                                Thanks Colin.

                                So back to VBR- (I've been using 2-Pass VBR for about 5 years).

                                 

                                Why would a 1.5 min 8mbs H.264, encoded in Sorenson, give me a 110 MB file (that says it's 8mbs), but the same project, encoded in Media Encoder, give me a 35 MB file that says it's 2.5mbs? Still confused...

                                • 13. Re: Media Encoder creates lower bitrate H.264 than I select?
                                  Colin Brougham Community Member

                                  Well, I've noticed with most interframe encodings, and H.264 VBR in particular, that you can get some pretty wide variances in file size. Sorenson and AME both use the MainConcept H.264 encoder (I'm assuming you're using the MC encoder in Squeeze, but if not, that might explain some differences), but the way that various encoding parameters are passed to the actual encoder from the UI may vary. That can translate to some big differences in file size.

                                   

                                  In MediaInfo, you should see two bitrates for at least the AME encode; one will be the "maximum" bit rate as set by the encoder, and the other will be actual, aggregate/average bit rate. The latter is the primary determinant of file size.

                                   

                                  The most important thing: do the encodes look roughly the same? If they do, the file size and bit rate don't matter too much--I assume you'd be happy with the smaller file then. If they ARE different--vastly so--then there are other parameters that might have to be looked at.

                                   

                                  What happens if you export an 8mbps CBR file from AME?

                                  • 14. Re: Media Encoder creates lower bitrate H.264 than I select?
                                    chuck farris Community Member

                                    Yes to MC encoder in Squeeze.

                                     

                                    And I forgot to mention I did do a test in CBR (which I don't usually use), and actually at a set rate of 9000, MediaInfo said "Overall bit rate: 2 309 Kbps"

                                     

                                    Now would it be crazy to say I don't see a huge difference, but that I'm just used to these rates and file sizes, so that's what I'm trying to duplicate, just in case there's a drop in quality I might not be noticing?

                                    • 15. Re: Media Encoder creates lower bitrate H.264 than I select?
                                      JSS1138 CommunityMVP

                                      That's not the case with H.264

                                       

                                      Well how about that.

                                       

                                      2-pass VBR will always trump CQ for quality and usually size

                                       

                                      Not sure how you can claim that.  Either can produce the superior quality file, depending on the settings used.  And you can't compare them directly, as VBR specifies a bitrate, and CQ specifies a quantization level.

                                       

                                      The advantage of using CQ mode is that you do get to specify that quality, whereas with VBR and CBR, the quality varies.

                                      • 16. Re: Media Encoder creates lower bitrate H.264 than I select?
                                        Ryan06

                                        I've actually recently had this same issue.  I was compressing a short film I exported from FCP at ProRes422 (bitrate between 50-75mb/s most likely).  I always use H.264 1080p @ 15-20mb/s, and let Vimeo/YouTube do their encode to reduce quality loss (hence my higher bitrate selection).  Most files come out within that scope of bitrate.  If I had issues, I'd close AME, reopen, recompresses - all is fine.  Not this file.  15-20mb/s turned out to being about 6.5 mb/s and I saw a lower quality image.

                                         

                                        However, if I selected a MUCH higher (non-web) bitrate, the final output increased.  25-35mb/s turned into about 13mb/s.  Better, though I'm going to try again to get a comfortable bitrate.

                                         

                                        The film takes place in the evening, so there are lower lit scenes, and one that uses more slightly brighter lighting.  I've heard of encoders using that Variable Bit Rate to scan brightness/darkness in footage, brightness indicating more detail (requiring higher bitrate) and darker imagery producing less detail.  That's the only thing I can think of for my project.  I have another film that continues the storyline, and 90% of footage is filmed during the day, mostly natural light.  I'm curious if this makes a difference in how the encoder treats the footage.

                                         

                                        It seems to be only select files, and not all rules apply to everything.  It's weird and frustrating.  Anyone have suggestions on achieving a bitrate that you intended to get?

                                        • 17. Re: Media Encoder creates lower bitrate H.264 than I select?
                                          Rallymax-forum Community Member

                                          The shipped h.264 encoder (Main Concept SDK) is notorious for dropping subtle gradiants as you would see in low light.

                                          That's why you're seeing a low bitrate - it's treating large areas as big blocks of the same color.

                                          If you want to keep that detail you need to change to another encoder like x264pro. It has "Adaptive Quality". - A slider bar that puts bits back into the background detail at the expense of the moving forground objects. This can make a huge difference in the overall image quality.

                                           

                                          This image is a good example of how backgound flat areas (the man's tie) can be saved by changing where the bits are allocated...

                                          http://www.x264pro.com/wp-content/uploads/MC_vs_X264PRO_Seq3_0_540x304.png

                                          http://www.x264pro.com/wp-content/uploads/MC_vs_X264PRO_Seq3_0_cropped.png

                                          • 18. Re: Media Encoder creates lower bitrate H.264 than I select?
                                            Ryan06 Community Member

                                            Very interesting, I knew the light avialable had an impact on encoded image quality.  Unfoetunately I have Mac OS 10.6, but hope to make an upgrade soon.  Thanks for that info!