[FFmpeg-user] Is mixing of audio channels happening by default in ffmpeg?

Carl Eugen Hoyos cehoyos at ag.or.at
Thu Jul 18 15:47:16 CEST 2013

Sam Marrocco <smarrocco <at> ringsidecreative.com> writes:

> On 7/18/2013 9:30 AM, Carl Eugen Hoyos wrote:
> Sam Marrocco <smarrocco <at> ringsidecreative.com> writes:
> > Is it possible to manually (through commandline args)
> > tell it to copy all streams across without the
> > (apparently bugged) -map 0 option?
> How is this option bugged?
> Perhaps I am reading what you wrote incorrectly:
> "Note that if you specify -map 0 (to copy all streams), all
> output audio tracks except the first one will be silent....
> This is probably trivial to fix "
> If when asked to copy all the streams with -map 0 
> (implying they will be copied as is) they are copied 
> silent (without sound?) doesn't that imply that it does 
> not work correctly? 

Sorry I am not a native speaker and probably did not 
explain well.

In the past, when a mov file was written with more than 
one audio stream, all audio streams were marked as 
"default" streams, meaning if you prepared a mov file 
for an iDevice containing a movie with several language 
tracks, all tracks were played simultaneously on playback.
(Making the feature of muxing several audio tracks into 
mov useless to some degree.)

A change was committed that marked the first of several 
audio tracks as "default" and all other tracks as "non-
default" (or as I badly named it: "silent").
This allows to select the language you like at playback 
and at the same time default playing (without selecting 
a language) works fine.

There is apparently a usecase (that I still don't 
understand completely) where you want all audio tracks to 
be marked as "default" (or non-silent).
I am searching for a volunteer to help me testing this 

Note that even for the mentioned use-case that currently 
does not work out-of-the-box, it is still possible to 
activate the silent tracks in your application (iiuc).

Carl Eugen

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