[FFmpeg-user] How to create a multichannel wav file without a specific channel layout

[Robert Krüger]

Hi Tobias,

On Mon, Sep 26, 2016 at 3:58 PM, Tobias Rapp <t.rapp at noa-archive.com> wrote:

> On 26.09.2016 13:10, Robert Krüger wrote:
>
>> Hi,
>>
>> On Mon, Sep 26, 2016 at 12:42 PM, Carl Eugen Hoyos <ceffmpeg at gmail.com>
>> wrote:
>>
>> 2016-09-26 12:17 GMT+02:00 Robert Krüger <krueger at lesspain.software>:
>>>
>>> I would like to know if it is possible to create a wave file that
>>>>
>>> contains
>>>
>>>> n channels of audio which do not have a channel layout like 5.1 or
>>>>
>>> stereo,
>>>
>>> (I assumed n==1 here because it should work fine for n>2)
>>>
>>> much like a file used in broadcast for just storing n signals in one wav
>>>> file.
>>>>
>>>
>>> It works fine for >16bit or >48kHz.
>>> I just sent a patch that fixes it for all (pcm) audio, that will not fix
>>> the
>>> front center (mono) case though: If this is an issue (if your software
>>> does not default to front center for 1-channel pcm wav), please
>>> tell me;-)
>>>
>>>
>>>
>>> Thanks for the quick reply! I meant something like writing a 4,6 or
>> 8-channel wav that just really contains 4,6,8 mono channels. E.g. some
>> cameras or other multi-track recording devices generate signals like these
>> and I would like to be able to put them in one wav file for archiving or
>> later processing.
>>
>
> If the input file doesn't have a channel mask you should be able to use
> the "-guess_layout_max 0" input option.
>
> Reading a bit through a few specs I am not sure whether
>> this requires using RF64 features (specifically the new constant
>> SPEAKER_ALL 0x80000000 for the channel assignment) and, to be honest, if
>> that makes sense at all.
>>
>
> In my opinion an undefined channel mask makes sense in your case. I'm in a
> very similar situation when recording AVI files with PCM audio and there I
> use the "-write_channel_mask off" output option.
>
> You don't need RF64 features, see section "Details about dwChannelMask" in
> https://msdn.microsoft.com/en-us/library/windows/hardware/dn653308.aspx :
>
> "If, for example in a multi-channel audio authoring application, no
> speaker location is desired on any of the mono streams, the
> dwChannelMask should explicitly be set to 0."
>
> Best regards,
> Tobias
>

Thanks a lot! That was exactly the information I was looking for.

Best regards,

Robert