[FFmpeg-user] Audio Stream Mapping issue

[Tim Nicholson]

On 15/11/11 16:08, Clément Bœsch wrote:
> On Tue, Nov 15, 2011 at 03:27:48PM +0000, Tim Nicholson wrote:
>> On 15/11/11 10:19, Clément Bœsch wrote:
>>> On Tue, Nov 15, 2011 at 02:05:35AM -0800, hughht5 wrote:
>>>> I would use the -map_channel option, however the documentation says it is
>>>> limited at the moment:
>>>>
>>>> (From http://ffmpeg.org/ffmpeg.html)
>>>> Note that "-map_channel" is currently limited to the scope of one input for
>>>> each output; you can’t for example use it to pick multiple input audio files
>>>> and mix them into one single output.
>>>>
>>>
>>> AFAIU, Tim only has one file so it doesn't apply here.
>>>
>>
>> Quite so.
>>
>>> Tim, I'm not sure to understand what you really want from your 4 stereo
>>> audio streams. I can't tell if you want to pick only some (then -map) or
>>> actually merge the channels of each streams into one single audio stream
>>> (then what you need is indeed the -map_channel feature).
>>>
>>
>> All I actually wanted to do was rewrap mxf->mov with no other
>> changes. (They were in fact 4 mono streams mxf does not support
>> stereo streams afaik)
>>
>
> My bad, I misread it was mono.
>
>> ffmpeg -i in.mxf -map 0 -vcodec copy -acodec copy tim2.mov
>>
>> or more succinctly:-
>>
>> ffmpeg -i in.mxf -map 0 -c copy tim2.mov
>>
>> performs this.
>>
>> However according to the documentation the -map 0 *should* be
>> unnecessary as the default *should* be "for audio the highest
>> channel count" wheeras it seems to be the first audio stream only.
>>
>
> The documenation sounds quite obvious to me; the selection pick "the
> best", and in case of score equality, only the first one is picked. Maybe
> it should indeed be explicited, or the behaviour changed.
>

In my experience, of much documentation writing and editing of others 
write ups, something that is abundantly clear to the writer can be 
completely misinterpreted by end users approaching things from a 
different starting point, it seems to be the way of things. That is why 
I first rasied the issue here to try and get a consensus of what the 
expected behaviour should be, and then try and understand how the 
documentation can be read to mean that...

I am not sure where you get the 'pick "the best"' from the 
documentation, it only says this for video, not audio!

I am happy to contribute to better wording, once I understand what the 
"correct" behaviour is.


> Sorry for the first misunderstanding, I'll do some checks and send a patch
> for this in a while if no one does.

> 					


-- 
Tim


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