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

[Reuben Martin]

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