[FFmpeg-user] sound balance on several files

jacky renaux.jacky at orange.fr
Wed Mar 28 12:37:23 CEST 2012

Le 28/03/2012 10:31, John Saturday a écrit :
> Read chapter 2 and end table of document:
> http://www.dolby.com/uploadedFiles/Assets/US/Doc/Professional/18_Metadata.Guide.pdf
> Normalize to multiply of 3 dB level (-15, -18, -21 dB ...) without
> clips. I use Audacity ( http://audacity.sourceforge.net/download/ ):
> Analyze / Contrast... to see clips at waveform check View / Show
> Clippings.
> This is an actual level of right channel... to balance channels Split
> Stereo Track (dropdown menu left at waveform), remove one channel and
> measure contrast (dialogue level); Undo, remove other channel and
> measure... Undo and amplify each channel separately and Make Stereo
> Track (dropdown menu left at waveform).
> DVD producers usually normalized at -27 dB but this is not a fixed
> standard. First you need to measure and choice dialogue level for your
> files: load files one by one, amplify to not clipping level and round
> down measured contrast to multiply of 3 dB... After this choice your
> dialogue level and calculate volume parameter for FFmpeg.
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many thanks John
I start to better undestand, I did read the paper and gave me a 
direction to look at

I found an interresting one

then is it obvious it depend on sound coder setting , il will go more 
into details
it is quite difficult to figure out what level is dbFS for mp3, aac and 
ac3, I will avoid ac3 at
it is not compatible with flv container
I do only streams speachs then either mp3 or aac are still eligible to 
be selected
I cannot use audacity as it does not read flv container (I did not succed)

there are still confusion (for me on)
depending on sound format used
   which metadata name I should specify
   would this metadata be forwarded by the red5 streaming server (rtmp mode)
   does customer located player will handle such

then I will explore few tracks

Now with you answer, I know what are the points to look at
thanks you to gave me a great help


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