Help is needed in avidemux

[D33]

Hello! I'm trying to burn .ass subtitles file to a mp4 video with the help of avidemux 2.7.3.
I chose from video output: Mpeg4 AVC(x264)

Then filters>subtitles>I chose my ASS subtitle file.

Audio Output:copy

Output Format:mp4Muxer .(In previous versions I chose Mp4v2Muxer and got a frame rate of 24.9 out of a 25 fps video, so I don't use Mp4v2Muxer any more.)

The problem is that I get a Variable Audio Bit rate mode with these settings, when in the orginal file, it says constant Audio Bit rate.
I also noticed in Overall bit rate mode : Variable, in General settings.

when I play the file in vlc it seems fine and no audio out of sync, but this is only a 1 minute video, and I don't know what the right settings to chose from.

Here is what mediainfo says about the original video:

Complete name : Express.mp4
Format : MPEG-4
Format profile : Base Media
Codec ID : isom (isom/iso2/avc1/mp41)
File size : 17.5 MiB
Duration : 53 s 59 ms
Overall bit rate : 2 763 kb/s
Movie name :

Description :
Recorded date : 20160710
Writing application : Lavf57.83.100
Comment :

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4
Format settings : CABAC / 3 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 3 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 53 s 0 ms
Bit rate : 2 633 kb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 25.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.051
Stream size : 16.6 MiB (95%)
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709
Codec configuration box : avcC

Audio
ID : 2
Format : AAC LC
Format/Info : Advanced Audio Codec Low Complexity
Codec ID : mp4a-40-2
Duration : 53 s 59 ms
Bit rate mode : Constant
Bit rate : 126 kb/s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 44.1 kHz
Frame rate : 43.066 FPS (1024 SPF)
Compression mode : Lossy
Stream size : 814 KiB (5%)
Default : Yes
Alternate group : 1


--------------------------------------------------------
Here is the output of the file after I burn the subtitles:

Complete name : iExpressEnSub.mp4
Format : MPEG-4
Format profile : Base Media
Codec ID : isom (isom/iso2/avc1/mp41)
File size : 27.1 MiB
Duration : 53 s 0 ms
Overall bit rate mode : Variable
Overall bit rate : 4 296 kb/s
Writing application : Lavf58.20.100

Video
ID : 1
Format : AVC
Format/Info : Advanced Video Codec
Format profile : High@L4
Format settings : CABAC / 4 Ref Frames
Format settings, CABAC : Yes
Format settings, Reference frames : 4 frames
Codec ID : avc1
Codec ID/Info : Advanced Video Coding
Duration : 53 s 0 ms
Bit rate : 4 163 kb/s
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate mode : Constant
Frame rate : 25.000 FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8 bits
Scan type : Progressive
Bits/(Pixel*Frame) : 0.080
Stream size : 26.3 MiB (97%)
Writing library : x264 core 146 r2538 121396c
Encoding settings : cabac=1 / ref=3 / deblock=1:0:0 / analyse=0x3:0x133 / me=hex / subme=7 / psy=1 / psy_rd=1.00:0.00 / mixed_ref=1 / me_range=16 / chroma_me=1 / trellis=1 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=6 / lookahead_threads=1 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=3 / b_pyramid=2 / b_adapt=1 / b_bias=0 / direct=1 / weightb=1 / open_gop=0 / weightp=2 / keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=40 / rc=crf / mbtree=1 / crf=20.0 / qcomp=0.60 / qpmin=10 / qpmax=51 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
Codec configuration box : avcC

Audio
ID : 2
Format : AAC LC
Format/Info : Advanced Audio Codec Low Complexity
Codec ID : mp4a-40-2
Duration : 52 s 965 ms
Bit rate mode : Variable
Bit rate : 126 kb/s
Maximum bit rate : 128 kb/s
Channel(s) : 2 channels
Channel layout : L R
Sampling rate : 44.1 kHz
Frame rate : 43.066 FPS (1024 SPF)
Compression mode : Lossy
Stream size : 813 KiB (3%)
Default : Yes
Alternate group : 1

-------------------------------------------------------------
I'm still new to all this encoding softwares, please help me to chose the right settings for this video.It is very important to me to understand this .


Also- I wanted to ask-the original file' data rate: 2633 kbps and total bitrate:2759 kbps (in 'details' when right click...)
and the file with the burned subtitles : data rate: 4163 kbps and total bitrate:4289 kbps.

Is the high data rate and total bitrate good? I appreciate any help in this matter. Thank you.

[davexnet]

The video bitrate is what you get based on the default settings and specific properties (complexity and noise)
of the source that affect compression.
Variable Vs. constant audio is something in the header, the audio itself if you used "copy" would not be re-encoded.
Nothing to worry about

[D33]

Thank you so much for your answer, you helped me a lot!