@Mosu
Re-muxing a video that has a FLAC audio track and using split mode by parts don't seem to work, maybe you can take a look or maybe somebody else can verify it.
Code:
G: Matroska, 28.9 MiB, 2 min 49 s, 1 430 kb/s
V: HEVC, Main 10@L3.1@Main, 1280x720, 23.976 FPS, 2 088 kb/s
A: German, FLAC, 1 291 kb/s, 2ch, 44.1 kHz
General
CompleteName : C:\Users\frank\Desktop\aaa.mkv
Format/String : Matroska
Format_Version : Version 4
FileSize/String : 28.9 MiB
Duration/String : 2 min 49 s
OverallBitRate_Mode/String : Variable
OverallBitRate/String : 1 430 kb/s
Encoded_Date : UTC 2020-03-29 18:20:06
Encoded_Application/String : mkvmerge v44.0.0 ('Domino') 64-bit
Encoded_Library/String : libebml v1.3.10 + libmatroska v1.5.2
Video
ID/String : 1
Format/String : HEVC
Format/Info : High Efficiency Video Coding
Format_Profile : Main 10@L3.1@Main
CodecID : V_MPEGH/ISO/HEVC
Duration/String : 11 s 220 ms
BitRate/String : 2 088 kb/s
Width/String : 1 280 pixels
Height/String : 720 pixels
DisplayAspectRatio/String : 16:9
FrameRate_Mode/String : Constant
FrameRate/String : 23.976 (23976/1000) FPS
FrameRate_Original/String : 23.976 (24000/1001) FPS
ColorSpace : YUV
ChromaSubsampling/String : 4:2:0
BitDepth/String : 10 bits
Bits-(Pixel*Frame) : 0.095
StreamSize/String : 2.79 MiB (10%)
Encoded_Library/String : x265 3.3+10-g08d895bb6:[Windows][GCC 9.3.0][64 bit] 10bit
Encoded_Library_Settings : removed, was too long
Default/String : Yes
Forced/String : No
colour_range : Limited
colour_primaries : BT.709
transfer_characteristics : BT.709
matrix_coefficients : BT.709
Audio
ID/String : 2
Format/String : FLAC
Format/Info : Free Lossless Audio Codec
CodecID : A_FLAC
Duration/String : 2 min 49 s
BitRate_Mode/String : Variable
BitRate/String : 1 291 kb/s
Channel(s)/String : 2 channels
ChannelLayout : L R
SamplingRate/String : 44.1 kHz
FrameRate/String : 9.571 FPS (4608 SPF)
BitDepth/String : 24 bits
Compression_Mode/String : Lossless
StreamSize/String : 26.1 MiB (90%)
Encoded_Library/String : Lavf58.38.101
Language/String : German
Default/String : No
Forced/String : No
FLAC file was created with ffmpeg:
D:\Projekte\VB\staxrip\bin\Apps\Encoders\ffmpeg\ffmpeg.exe -i "D:\Samples\aaa_temp\aaa ID1.m4a" -af volume=1.7dB -y -hide_banner -ac 2 "D:\Samples\aaa_temp\aaa ID1.flac"
edit:
Happens also with FLAC created with eac3to.