Variable bit rate (VBR) output with constant bit rate (CBR) settings?

Question

Hi,I am trying to transcode a SD clip via compressor. Here&#x27;s the settings that I would like to achieve. Video Frame Rate25 fpsVideo StandardPALVideo CodecMPEG-2 Video, Main Profile/Main LevelAudio CodecMPEG-2 Audio Layer II orAvailable audio codecContainer FormatMpeg-2 Transport Stream  (mpg)Video bit rate8,000 Kbps, CBRAudio Bit rate384 KbpsAspect Ratio16:9 Audio Sample Rate48KHzResolution1024x576Scan typeProgressiveHowever, the only problem I have is transcoding the clip to CBR mode. Even though I have chosen the &#x27;one-pass CBR mode&#x27; in Compressor, the output is still VBR mode. Is there any way for Compressor to follow the settings and achieve the CBR mode? Thanks in advance.

Russ H · Answer

I don&#x27;t experience ythat. Where is it being reported as VBR? When I do a test clip and bring it into Media INFO, it reports as CBR. Same in MPEG Streamclip.Russ

shrnh · Answer

Hi Russ,Thanks for your reply. I am using Compressor 3.5.3, not sure if this affects the result (as below and underlined for areas that are not achievable. I wish I could e-mail you the droplet.Format                                   : MPEG-TSFile size                                : 31.3 MiBDuration                                 : 30s 176msOverall bit rate mode                : VariableOverall bit rate                         : 8 705 KbpsVideo ID                                  : 4096 (0x1000)Menu ID                                  : 1 (0x1)Format                                    : MPEG VideoFormat version                         : Version 2Format profile                           : Main@MainFormat settings, BVOP             : YesFormat settings, Matrix              : CustomFormat settings, GOP                : M&#x3D;3, N&#x3D;12Codec ID                                   : 2Duration                                    : 30s 0msBit rate                                     : 7 887 KbpsMaximum bit rate                       : 8 000 KbpsWidth                                        : 720 pixelsHeight                                       : 576 pixelsDisplay aspect ratio                    : 16:9Frame rate                                 : 25.000 fpsStandard                                    : PALColor space                                : YUVChroma subsampling                   : 4:2:0Bit depth                                    : 8 bitsScan type                                   : ProgressiveCompression mode                     : LossyBits/(Pixel*Frame)                      : 0.761Stream size                               : 28.2 MiB (90%)Color primaries                          : BT.601 PALTransfer characteristics              : BT.470 System B, BT.470 System GMatrix coefficients                      : BT.601AudioID                                           : 4098 (0x1002)Menu ID                                    : 1 (0x1)Format                                     : MPEG AudioFormat version                          : Version 1Format profile                             : Layer 2Codec ID                                   : 3Duration                                    : 30s 0msBit rate mode                            : ConstantBit rate                                      : 384 KbpsChannel(s)                                 : 2 channelsSampling rate                            : 48.0 KHzCompression mode                    : LossyStream size                              : 1.37 MiB (4%)MenuID                                             : 110 (0x6E)Menu ID                                  : 1 (0x1)List                                           : 4096 (0x1000) (MPEG Video) / 4098 (0x1002) (MPEG Audio)Maximum bit rate                      : 8797600

Russ H · Answer

No. I just tried C3.5 and was able to get a PAL sized CBR.Try a new job and not the droplet. in the Inspector&gt;Encoder&gt;Video Format, set to PAL.What app are you using to get the reported A/V info in your preceding post?Russ

shrnh · Answer

Hi Russ, I&#x27;ve change a new job and tried again. It is still the same. 😟I used Media Info.

Russ H · Answer

Could you post screen shots of your latest attempt? of the batch window…in the Inspector, the settings in Summary and Encoding panes?Russ

Russ H · Answer

ANd if I don&#x27;t post any more tonight it&#x27;s because I have the mother of all colds and am going to bed shortly.

shrnh · Answer

Hi Russ, Here&#x27;s the images.

shrnh · Answer

Take care and rest well!

Russ H · Answer

The only thing I notice is your extension, which should be m2t.You started with the Transport STream preset, correct?Russ

Russ H · Answer

Just to add…what was your original footage – format and camera?I don&#x27;t have any SD native progressive footage to test, although I can shoot some later today.Russ

shrnh · Answer

Hi Russ,Hope u are feeling much better. Yes I did. I changed the name extension to mpg. The original footage is 1920x1080p, Apple ProRes 422. Hope this helps.

Russ H · Answer

Take your 1080p file and re-size it to a SD Pro Res file. Then take that file into a new job and do your MTS encode. You should be able to get a CBR from the SD source file.Russ

Russ H · Answer

Just wondering whether you had any luck in getting CBR if you took my suggestion and first down-scaled your 1080p file to standard definition Pro Res and then encoded that SD file to MPEG.Russ

shrnh · Answer

Hi Russ,I have tried to export to SD ProRes and then transcode to mpg in Compressor. However, it still comes out the same (VBR mode). 😟

Russ H · Answer

I&#x27;ll be darned.I know C will not make a CBR MPEG from a high def file. And that&#x27;s why I suggested the extra step to PR SD.I&#x27;ll think about it some more, but right now I&#x27;m out of ideas why it works here but not for you.Russ

Video Frame Rate	25 fps
Video Standard	PAL
Video Codec	MPEG-2 Video, Main Profile/Main Level
Audio Codec	MPEG-2 Audio Layer II or Available audio codec
Container Format	Mpeg-2 Transport Stream (mpg)
Video bit rate	8,000 Kbps, CBR
Audio Bit rate	384 Kbps
Aspect Ratio	16:9
Audio Sample Rate	48KHz
Resolution	1024x576
Scan type	Progressive