FFAStrans forum

Hello. After encoding mxf, I get mp 4, with a constant bitrate parameter. Tell me how to change the "Bit rate mode: Constant" parameter to variable? What parameter should you set?

Format : MPEG-4
Format profile : Base Media / Version 2
Codec ID : mp42 (isom)
File size : 18.3 MiB
Duration : 4 min 48 s
Overall bit rate mode : Variable
Overall bit rate : 532 kb/s
Encoded date : UTC 2021-05-17 12:33:57
Tagged date : UTC 2021-05-17 12:33:57

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : Main@L4
Format settings : CABAC / 5 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference : 5 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 4 min 48 s
Bit rate mode : Variable
Bit rate : 402 kb/s
Maximum bit rate : 450 kb/s
Width : 720 pixels
Height : 576 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant

Format : MPEG-4
Format profile : Base Media
Codec ID : isom (isom/iso2/avc1/mp41)
File size : 34.6 MiB
Duration : 8 min 5 s
Overall bit rate : 597 kb/s
Encoded date : UTC 2021-05-24 12:24:56
Tagged date : UTC 2021-05-24 12:24:56

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : Main@L4
Format settings : CABAC / 5 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference : 5 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 8 min 5 s
Bit rate : 450 kb/s
Width : 720 pixels
Height : 576 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 25.000 FPS
Standard : PAL
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.043
Stream size : 27.0 MiB (78%)

The H.264 encoder is essentially just x264, which means that you can specify custom parameters underneath it.
What you're gonna need for CBR is pretty straightforward and it's:

--nal-hrd cbr

Cheers,
Frank