FFmpeg check channels of a 7.1 audio for silence - audio

This is a follow-up question from my previous question asked here, where I needed to look for silence within a specific audio track. Here is the ffmpeg life-saver solution where helps to get some metadata:
ffmpeg -i file -map 0:a:1 -af astats -f null -
But I have other type of input .mp4 files where they have one single track of 8 (i.e. 7.1) audio channels. Apparently these files are transcoded from an original file (somehow the 4 track stereos are squished into these files). Now similar to my previous, I need to know if the original file was 2-channel stereo or 5.1 (6) channel.
How to know if a specific channel of an audio track (say Center channel) is silent/mute, possibly using ffmpeg? Here is a sample .mp4 file.


You can use the channelsplit filter to split the audio channels and run silencedetect on each.
Example:
ffmpeg -i test2.mp4 -filter_complex "[0:a]channelsplit=channel_layout=7.1:channels=FC[fc];[fc]silencedetect" -f null /dev/null
You can find more on audio channel manipulation here:
https://trac.ffmpeg.org/wiki/AudioChannelManipulation


There is also the astats filter which can be used to detect silent tracks/channels.
This i what it outputs for the channel 4 of the suggest test file, which appears indeed to be perfectly silent.
ffmpeg -i "$in" -vn -sn -dn -map 0:a -af "astats=measure_overall=none" -f null -
...
[Parsed_astats_0 # 0x6beed00] Channel: 4
[Parsed_astats_0 # 0x6beed00] DC offset: 0.000000
[Parsed_astats_0 # 0x6beed00] Min level: 0.000000
[Parsed_astats_0 # 0x6beed00] Max level: 0.000000
[Parsed_astats_0 # 0x6beed00] Min difference: 0.000000
[Parsed_astats_0 # 0x6beed00] Max difference: 0.000000
[Parsed_astats_0 # 0x6beed00] Mean difference: 0.000000
[Parsed_astats_0 # 0x6beed00] RMS difference: 0.000000
[Parsed_astats_0 # 0x6beed00] Peak level dB: -inf
[Parsed_astats_0 # 0x6beed00] RMS level dB: -inf
[Parsed_astats_0 # 0x6beed00] RMS peak dB: -inf
[Parsed_astats_0 # 0x6beed00] RMS trough dB: -inf
[Parsed_astats_0 # 0x6beed00] Crest factor: 1.000000
[Parsed_astats_0 # 0x6beed00] Flat factor: -inf
[Parsed_astats_0 # 0x6beed00] Peak count: 6057984
[Parsed_astats_0 # 0x6beed00] Bit depth: 0/0
[Parsed_astats_0 # 0x6beed00] Dynamic range: -inf
[Parsed_astats_0 # 0x6beed00] Zero crossings: 0
[Parsed_astats_0 # 0x6beed00] Zero crossings rate: 0.000000
[Parsed_astats_0 # 0x6beed00] Number of NaNs: 0
[Parsed_astats_0 # 0x6beed00] Number of Infs: 0
[Parsed_astats_0 # 0x6beed00] Number of denormals: 0
[Parsed_astats_0 # 0x6beed00] Channel: 5
...
Something like this would show an overview of all channels:
ffmpeg -i "$in" -vn -sn -dn -map 0:a -af "astats=measure_overall=none" -f null - 2>&1 \
| egrep 'Channel|(Max|Peak) level'
[Parsed_astats_0 # 0x7567d00] Channel: 1
[Parsed_astats_0 # 0x7567d00] Max level: 0.978271
[Parsed_astats_0 # 0x7567d00] Peak level dB: -0.190818
[Parsed_astats_0 # 0x7567d00] Channel: 2
[Parsed_astats_0 # 0x7567d00] Max level: 0.978271
[Parsed_astats_0 # 0x7567d00] Peak level dB: -0.190818
[Parsed_astats_0 # 0x7567d00] Channel: 3
[Parsed_astats_0 # 0x7567d00] Max level: 0.000006
[Parsed_astats_0 # 0x7567d00] Peak level dB: -103.162709
[Parsed_astats_0 # 0x7567d00] Channel: 4
[Parsed_astats_0 # 0x7567d00] Max level: 0.000000
[Parsed_astats_0 # 0x7567d00] Peak level dB: -inf
[Parsed_astats_0 # 0x7567d00] Channel: 5
[Parsed_astats_0 # 0x7567d00] Max level: 0.000006
[Parsed_astats_0 # 0x7567d00] Peak level dB: -103.162709
[Parsed_astats_0 # 0x7567d00] Channel: 6
[Parsed_astats_0 # 0x7567d00] Max level: 0.000006
[Parsed_astats_0 # 0x7567d00] Peak level dB: -103.162709
[Parsed_astats_0 # 0x7567d00] Channel: 7
[Parsed_astats_0 # 0x7567d00] Max level: 0.978271
[Parsed_astats_0 # 0x7567d00] Peak level dB: -0.190818
[Parsed_astats_0 # 0x7567d00] Channel: 8
[Parsed_astats_0 # 0x7567d00] Max level: 0.978271
[Parsed_astats_0 # 0x7567d00] Peak level dB: -0.190818

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if I break the above command as below
awk '{
if(NR%8==2){a=$3;b=$4};
if(NR%8==4){a=$8","$7","a};
if(NR%8==5){b=$8","$7","b};
if(NR%8==6){c=$1;d=$2};
if(NR%8==7){
if(c!=-1.000000)print a,$0;
if(d!=-1.000000)print b,$0
}
}' inputfilename
I am storing the output details in a and b from the beginning while reading file line by line like NR%8==2 is line 2 , NR%8==4 is line 4 of file and so on. At the 7th line (NR%8==7), I am checking for values c and d stored from line 6 (NR%8==6), if c and d has mismatch values we will print the output with 7th line content.

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