XMedia Recode output Overall bit rate mode CBR？

[zglloo]

I have been trying to speed up transcoding MP4 or MPEG-TS files, but I found that the total bit rate of the output is still VBR.
I have tried CPU and GPU！Will the GPU not be transcoded to CBR?

General
ID                                       : 1 (0x1)
Complete name                            : C:\Users\zgllo\Videos\歌_2.ts
Format                                   : MPEG-TS
File size                                : 3.81 MiB
Duration                                 : 9 s 520 ms
Overall bit rate mode                    : Variable
Overall bit rate                         : 3 348 kb/s

Video
ID                                       : 20 (0x14)
Menu ID                                  : 1 (0x1)
Format                                   : AVC
Format/Info                              : Advanced Video Codec
Format profile                           : High@L4
Format settings                          : 2 Ref Frames
Format settings, CABAC                   : No
Format settings, Reference frames        : 2 frames
Codec ID                                 : 27
Duration                                 : 9 s 560 ms
Bit rate mode                            : Constant
Bit rate                                 : 2 988 kb/s
Nominal bit rate                         : 2 500 kb/s
Width                                    : 1 920 pixels
Height                                   : 1 080 pixels
Display aspect ratio                     : 16:9
Frame rate                               : 25.000 FPS
Color space                              : YUV
Chroma subsampling                       : 4:2:0
Bit depth                                : 8 bits
Scan type                                : Interlaced
Scan type, store method                  : Separated fields
Scan order                               : Top Field First
Bits/(Pixel*Frame)                       : 0.058
Stream size                              : 3.41 MiB (89%)
Color range                              : Limited
Color primaries                          : BT.709
Transfer characteristics                 : BT.709
Matrix coefficients                      : BT.709

Audio
ID                                       : 21 (0x15)
Menu ID                                  : 1 (0x1)
Format                                   : MPEG Audio
Format version                           : Version 1
Format profile                           : Layer 2
Codec ID                                 : 3
Duration                                 : 9 s 600 ms
Bit rate mode                            : Constant
Bit rate                                 : 192 kb/s
Channel(s)                               : 2 channels
Sampling rate                            : 48.0 kHz
Frame rate                               : 41.667 FPS (1152 SPF)
Compression mode                         : Lossy
Delay relative to video                  : -10 ms
Stream size                              : 225 KiB (6%)

Menu
ID                                       : 4096 (0x1000)
Menu ID                                  : 1 (0x1)
Duration                                 : 9 s 520 ms
List                                     : 20 (0x14) (AVC) / 21 (0x15) (MPEG Audio)
Service name                             : Service01
Service provider                         : FFmpeg
Service type                             : digital television

[LigH.de]

The video encoder can flag the video stream to represent that the encoding mode was: "try to keep the bitrate rather constant, if possible"; but in general, it is not the case, bitrates of compressed video streams will always vary, only uncompressed video can have a constant bitrate. So don't count much on this flag in a video stream.

Audio streams can be forced to a constant bitrate. But this is mainly achieved by wasting space, by stuffing smaller frames. This flag is a bit more reliable.

The container, after all, is a third separate case. There are containers which may have special layouts for either constant or variable bitrate streams as content. Such a container in CBR layout may not be able to guarantee sync between video and audio if they have a variable bitrate instead. Other containers are per se "able to handle variable bitrates". This flag doesn't tell you much more than that.


Variable bitrate is nothing bad. Instead, it is the only way to keep the visual quality rather constant, despite variable video content ... a scene with fine details or much motion needs a lot more bitrate than a still scene of a misty landscape, or even a moment of blackness. You don't want a black fade waste as much bitrate as a high speed chase.

And it does not matter at all whether a CPU or a GPU encodes the video. VBR is easier to achieve than CBR, because the encoder has more freedom to respond to the requirements of the material. CBR is only useful when you have speed limits to read the encoded video (e.g. from a slow medium like an optical disc, or as a transfer via a network).

[zglloo]

hey LigH.de

Thanks for your answer, because the video has another problem with PCR jitter, I have no way to detect it through ETR101 290, and finally I actually use IPTV VOD to play