Downmixing 5.1 to 2.0 using ffmpeg

[xweel]

Hi,

The plex app on android tv/shield tv is pretty shit at downmixing 5.1 to stereo with loud scenes being extra loud and quite scenes being barely audible. Right now I'm using the scripts on this thread as a solution, which tbh is near perfect when using the 3rd script (loudnorm). But I feel like it could still be better. I wanna know if there's a way to check how PotPlayer on my PC is handling the downmixing and edit the ffmpeg scripts to reproduce the same results? (I tried so many different solutions to make plex handle this issue but nothing worked)

thank you.

[ProWo]

Try my clever FFmpeg GUI. It contains a special command line for downmixing 5.1 to stereo.
Load your video, click Main, click Modify Audio Stream, click Continue, select the output, select the bitrate, click 5.1 to 2 (Channels), click Convert. Done.
If you like the new audio file, remux it with the video.

[Hoser Rob]

Unless you're looking at this as a scripting exercise, what you want to do is SO much easier using Audacity. That's a very solid and well documented program.

[xweel]

I've used Audacity before, but never like this, so I'm not sure. I'll have a look at both clever ffmpeg gui and audacity. But what I want is to edit the script (which is a batch script) in a way that makes it copy exactly what the PotPlayer ffmpeg built in decoder is doing when I'm playing 5.1 audio.

[jagabo]

I wanna know if there's a way to check how PotPlayer on my PC is handling the downmixing

Preferences -> Audio (left pane) -> Mixer Level (right pane). But the defaults are simply 100 percent for each.

[xweel]

I did check that, but wasn't sure if that's what I was looking for because they were all at 100%, which I'm guessing is basically the first script on that plex thread I linked above.

[jagabo]

You're probably using the normalizer in addition to the mixer.

I've use this to boost the center channel on some recordings:

ffmpeg -y -i %1 -vcodec copy -ac 2 -af "pan=stereo|FL < FL+1.414FC+0.5BL+0.5SL+0.25LFE+0.125BR|FR < FR+1.414FC+0.5BR+0.5SR+0.25LFE+0.125BL" -acodec aac -b:a 160k "%~dpn1.new.mp4"

But that doesn't limit dynamic range.

[xweel]

This is the script I used

ffmpeg -y -i "%%A" -map 0:v -c:v copy -map 0:a:0? -c:a:0 copy -map 0:a:0? -c:a:1 aac -ac 2 -filter:a:1 "loudnorm" -ar:a:1 48000 -b:a:1 192k -metadata:s:a:1 title="Eng 2.0 Stereo" -metadata:s:a:1 language=eng -map 0:a:1? -c:a:2 copy -map 0:a:2? -c:a:3 copy -map 0:a:3? -c:a:4 copy -map 0:a:4? -c:a:5 copy -map 0:a:5? -c:a:6 copy -map 0:a:6? -c:a:7 copy -map 0:s? -c:s copy "ffmpegOut/%%~nA_Stereo_LoudNorm.mkv

now I 'm thinking I should just use this one instead. Will try now

ffmpeg -y -i "%%A" -map 0:v -c:v copy -map 0:a:0? -c:a:0 copy -map 0:a:0? -c:a:1 aac -b:a:1 192k -ac 2 -metadata:s:a:1 title="Eng 2.0 Stereo" -map 0:a:1? -c:a:2 copy -map 0:a:2? -c:a:3 copy -map 0:a:3? -c:a:4 copy -map 0:a:4? -c:a:5 copy -map 0:a:5? -c:a:6 copy -map 0:a:6? -c:a:7 copy -map 0:s? -c:s copy "ffmpegOut/%%~nA_Stereo.mkv"

[xweel]

First one has the loudnorm filter included, which I liked at first, but I'm not sure anymore. I want it to be as close as to what potplayer is doing on my PC

[jagabo]

I meant you are probably using potplayer's normalizer in addition to its mixer. It's the normalizer that's responsible for the reduced dynamic range, not the mixer.

[Zero-11]

here are the ffmpeg scripts, just rename .txt to .bat and execute the .bat with the ffmpeg.exe in the same folder
https://www.dropbox.com/sh/rebtkv4wtd9i7ra/AAD9FM4IVM5-_T5TgWBRhnDia?dl=0

"-ac 2" audio channels 2 bam it's downmixed

pushd "%2"

for /R %%A in (*.mp4, *.avi, *.mov, *.wmv, *.ts, *.m2ts, *.webm, *.mkv) do (
    echo Processing %%A
    ffmpeg -i "%%A" -c:v copy -c:a libvorbis -ar 32000 -ac 2 -b:a 112k -map 0 "%%~dnpA-p.mkv"
    echo Processed %%A
)
pause

[xweel]

This script seems perfect, but what does it do differently than the script I showed above? Is this closer to potplayer's downmixing? I don't think I'm using the normalizer in potplayer because it's not checked.
Also it keeps processing the output file after finishing the original file resulting in a never ending script xD

[jagabo]

Also it keeps processing the output file after finishing the original file resulting in a never ending script xD

Because the FOR loop sees the MKV file ffmpeg just created and proceeds to convert it too. Then when it's done with that there's another new MKV file to be processed, ad nauseam. It's stuck in an endless loop. You need to put the files in a different location. Or only convert non-MKV files to MKV files.

[ProWo]

pushd "%2"

for /R %%A in (*.mp4, *.avi, *.mov, *.wmv, *.ts, *.m2ts, *.webm, *.mkv) do (
    echo Processing %%A
    ffmpeg -i "%%A" -c:v copy -c:a libvorbis -ar 32000 -ac 2 -b:a 112k -map 0 "%%~dnpA-p.mkv"
    echo Processed %%A
)
pause

This script contains no downmix improvement...

[xweel]

I thought the script I used also had no improvements, but idk...

[CharlieRHCP]

Try my clever FFmpeg GUI. It contains a special command line for downmixing 5.1 to stereo.
Load your video, click Main, click Modify Audio Stream, click Continue, select the output, select the bitrate, click 5.1 to 2 (Channels), click Convert. Done.
If you like the new audio file, remux it with the video.

I need this for my plex to TV 2.0 setup, and I done it. But what to do with heimer_1_A_converted.aac file. How to get it to work with my movie.

"remux it with the video" what that mean?

[ProWo]

Try my clever FFmpeg GUI. It contains a special command line for downmixing 5.1 to stereo.
Load your video, click Main, click Modify Audio Stream, click Continue, select the output, select the bitrate, click 5.1 to 2 (Channels), click Convert. Done.
If you like the new audio file, remux it with the video.

I need this for my plex to TV 2.0 setup, and I done it. But what to do with heimer_1_A_converted.aac file. How to get it to work with my movie.

"remux it with the video" what that mean?

Start clever FFmpeg-GUI.
Load your movie, click main, click multiplex, drag & drop heimer_1_A_converted.aac into the frame, deselect all streams (on the left), select the video stream and the heimer_1_A_converted.aac stream, select your output container (mkv or mp4) and click multiplex.
Done.

[pandy]

ffmpeg offers other filters to perform audio dynamics compression (normalization)

https://ffmpeg.org/ffmpeg-filters.html#adynamicequalizer
https://ffmpeg.org/ffmpeg-filters.html#dynaudnorm

I use dynaudnorm - i would perform normal downmixing and audio compression of 2 channel result but i can imagine also other approaches.

[CharlieRHCP]

Try my clever FFmpeg GUI. It contains a special command line for downmixing 5.1 to stereo.
Load your video, click Main, click Modify Audio Stream, click Continue, select the output, select the bitrate, click 5.1 to 2 (Channels), click Convert. Done.
If you like the new audio file, remux it with the video.

I need this for my plex to TV 2.0 setup, and I done it. But what to do with heimer_1_A_converted.aac file. How to get it to work with my movie.

"remux it with the video" what that mean?

Start clever FFmpeg-GUI.
Load your movie, click main, click multiplex, drag & drop heimer_1_A_converted.aac into the frame, deselect all streams (on the left), select the video stream and the heimer_1_A_converted.aac stream, select your output container (mkv or mp4) and click multiplex.
Done.

Thanks for the quick and precise answer.