5 Replies Latest reply on Oct 8, 2009 1:57 PM by jdoranz5150

    CS4 Media Encoder- Two Pass CBR settings?


      I have come across something strange in the stand alone Adobe Media Encoder CS4 (Windows and Mac) when attempting to encode an FLV with on2vp6.


      There is an option under CBR that allows for a two pass, however it also has the minimum bitrate, maximum bitrate and bitrate variability options. This makes sense for VBR, but why are they there for in CBR?  Are they inactive for CBR? Shouldn't they be dimmed? Are you supposed to set to 100% and leave it? Is it a bug?   I know H.264 only has one pass, and it acts the same way as FLV/on2vp6 One Pass.


      One of the whole points CBR is that you have a defined bitrate with no variation, used predominantly for HTTP Pseudo Streaming or Streaming. I have a bitrate limit imposed on a server, so I add video and audio bitrates together and get the total bitrate and I want a steady stream. With minimum and maximum settings it would vary depending on your content hence the term VBR which seems contradictory to CBR...


      Can anyone please shed some light on this?


      Thanks in advance.


        • 1. Re: CS4 Media Encoder- Two Pass CBR settings?
          Harm Millaard Level 7

          That makes no sense. But I can't replicate it. This is what I get:


          08-10-2009 21-01-15.jpg

          • 2. Re: CS4 Media Encoder- Two Pass CBR settings?
            jdoranz5150 Level 1

            Hi thanks for your reply.


            It looks like you are in H.264 mode... Under Export settings, Format needs to be: FLV|F4V  then go under Multiplexing and choose FLV.

            Then choose CBR 2-Pass and that will replicate it.


            I am using version of Adobe Media Encoder on Windows, but I think all versions had this issue.



            • 3. Re: CS4 Media Encoder- Two Pass CBR settings?
              jdoranz5150 Level 1

              Sorry I meant looks like you are in F4V mode...(I said H.264)....  Once you choose FLV/F4V which you have for Format at the top of the window. Then  under the bottom tabs under Sumamry (Filters, Format, Video, Audio etc) choose Format:Basic Settings:Multiplexing: FLV


              Hope that clarifies, and thanks again.


              • 4. Re: CS4 Media Encoder- Two Pass CBR settings?
                Harm Millaard Level 7

                You are correct, I can replicate that, but what happens is that the undershoot and overshoot % change from single pass to 2-pass, so it does not seem illogical that even though you are using CBR, there is some bit allocation to harder parts (not really CBR) and less to easier parts. You have to keep in mind that although it is called CBR, it is not really Constant BR, but approximates it. Then a second pass can improve the difficult parts slightly. Notice that single pass gives 90% undershoot and 2-pass gives 80-120% undershoot-overshoot with 80% variability. So effectively it is kind of VBR.

                • 5. Re: CS4 Media Encoder- Two Pass CBR settings?
                  jdoranz5150 Level 1

                  Thanks again for the reply. The next question would be, is One Pass CBR then the only true CBR (or best for streaming/pseudo streaming)?


                  Adobe's Docs skipped right over that (2 Pass and CBR)...seems pretty important, maybe they figure most will just use One Pass for CBR.

                  The funny thing is you can't find any real references on the web to Two Pass CBR either. Even Google wants me to change it to VBR Two Pass in my searches :-)


                  The reason I ask is that when we ran Two Pass CBR, it flagged an error on the HTTP Psuedo Stream server (similar to Xmoov PHP) because it exceeded the bitrate limit at a portion of the video (evidentially) and stopped it in its tracks... Unless maybe it was a coincidence but it was tried several times supposedly. I didn't witness this, because we don't have access to the client's Intranet/VPN (long story). I built a JWPlayer/Xmoov PHP setup at our site to replicate, but it doesn't have the bandwidth throttling enabled to test that theory.   I will try to run some more tests and post back here if I find the anomaly.


                  I much prefer VBR 2-Pass anyway for quality but you can't really stream it effectively.