[FFmpeg-user] Audio channels mapping - Decklink SDI input

[j.santacruz at ndr.de]

>> Hi all,
>> 
>> I'm trying to encode Decklink SDI input and stream it to NDI and keep 
the
>> audio layout as is.
>> 
>> The SDI signal has 8 audio channels with the following layout:
>> 1,2 Stereo
>> 3,4 Stereo
>> 5,6 Dolby
>> 7,8 Stereo
>> 
>> What I need to do is to passthrough all audio channels and to keep the
>> layout as is.
>> 
>> Tried "-ac 8 -acodec copy" but it doesn't seem to be working.
>> Maybe I need to use something like "-map_channel" and then to define 
the
>> audio output layout BUT to do so I need to know
>> "stream_specifier.channel_id" and when I ffprobe the SDI input I get
>> "channel_layout=unknown" which I think is a known issue with Decklink 
cards
>> according to BM support forums
>> > There is no format detection options for audio capture to determine 
the
>> > number of audio channels provided by the video source.
>> 
>> Can anyone help with the correct command to passthrough the audio 
channels?
>> your inputs are highly appreciated.!

>There is no layout with SDI. It supports 16 channels of audio, and people 
can 
>use them for whatever they want. I?ve seen them used for everything from 
a 
>click track to a COM system relay. BM devices will provide you with 2,8 
or 16 
>channels depending on how you set it up. You will have to map them by 
channel 
>numer from the audio stream.

>-Reuben

Hi!
If I understand correctly, you'd like to pass through the audio layout 
from SDI to an ffmpeg stream. 
I think by default ffmpeg will only put the first two audio channels into 
the output.

If you want to specify which audio you'd like to pass thorugh you might 
use the '-map' option to select the correct streams or even use 
'-filter_complex' to do in depth mapping. It is a long time ago, I did 
something like this... But basically you need to see in the CLI output, 
which streams you want to use and map those to the output streams you 
want. 
Take a look at this doc:
https://www.ffmpeg.org/ffmpeg-filters.html#streamselect_002c-astreamselect
https://www.ffmpeg.org/ffmpeg-all.html#Stream-selection
https://ffmbc.wordpress.com/category/audio/

Best,
Jan




Von:    Reuben Martin <reuben.m at gmail.com>
An:     FFmpeg user questions <ffmpeg-user at ffmpeg.org>
Datum:  11.11.2018 02:52
Betreff:        Re: [FFmpeg-user] Audio channels mapping - Decklink SDI 
input
Gesendet von:   "ffmpeg-user" <ffmpeg-user-bounces at ffmpeg.org>



On Wednesday, November 7, 2018 6:47:32 PM CST Mustafa Al Ani wrote:
> Hi all,
> 
> I'm trying to encode Decklink SDI input and stream it to NDI and keep 
the
> audio layout as is.
> 
> The SDI signal has 8 audio channels with the following layout:
> 1,2 Stereo
> 3,4 Stereo
> 5,6 Dolby
> 7,8 Stereo
> 
> What I need to do is to passthrough all audio channels and to keep the
> layout as is.
> 
> Tried "-ac 8 -acodec copy" but it doesn't seem to be working.
> Maybe I need to use something like "-map_channel" and then to define the
> audio output layout BUT to do so I need to know
> "stream_specifier.channel_id" and when I ffprobe the SDI input I get
> "channel_layout=unknown" which I think is a known issue with Decklink 
cards
> according to BM support forums
> > There is no format detection options for audio capture to determine 
the
> > number of audio channels provided by the video source.
> 
> Can anyone help with the correct command to passthrough the audio 
channels?
> your inputs are highly appreciated.!

There is no layout with SDI. It supports 16 channels of audio, and people 
can 
use them for whatever they want. I?ve seen them used for everything from a 

click track to a COM system relay. BM devices will provide you with 2,8 or 
16 
channels depending on how you set it up. You will have to map them by 
channel 
numer from the audio stream.

-Reuben




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