[FFmpeg-user] Using two of the same devices with FFMPEG and Decklink enabled

looxonline looxonline at gmail.com
Wed Apr 20 16:02:22 CEST 2016

I've recently compiled FFMPEG on OSX with Decklink enabled. My machine has
two Decklink SDI 4K cards installed.

I can see both devices when I use the black magic GUI and capture from them
simultaneously through the command line if I use bmdtools. Unfortunately I
can't seem to do the same using FFMPEG.

When I list the devices with FFMPEG using:

ffmpeg -f decklink -list_devices 1 -i dummy

I get a response that shows that it can see both cards as below:

[decklink @ 0x7fe189800000] Blackmagic DeckLink devices:
[decklink @ 0x7fe189800000] 	'DeckLink SDI 4K'
    Last message repeated 1 times
dummy: Immediate exit requested

This tells me that it is seeing both cards but they are both being
referenced by exactly the same name, i.e. Decklink SDI 4K.

To capture from a Decklink source using FFMPEG the syntax below is used:

ffmpeg -f decklink -i 'DeckLink SDI 4K at 8' -acodec copy -vcodec copy

The issue that I have is that I can only capture the input from one card at
a time. If I try to run this command in two separate terminal windows it
does not identify that one card is being used and therefore the other should
be used. It simply throws an error.

Is anyone else using FFMPEG with DeckLink? Has anyone else encountered this
issue and found a solution? Should I create a request/bug?

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