[FFmpeg-user] Capture multiple streams into same container?

Tom Sparks tomasparks.ts at gmail.com
Wed Jun 24 12:41:58 EEST 2020

mkv is a better output format to use

On 24/06/2020, Simon Roberts <simon at dancingcloudservices.com> wrote:
> Greetings all, I'm a pretty low-level ffmpeg user, just doing screen
> captures, compressions, and some simple format conversions. I have not made
> much progress understanding more advanced key concepts; I apologize if this
> is a basic question.
> I have a four-input video capture card, (Blackmagic DeckLink) and I
> successfully built ffmpeg with support for that. I can capture using the
> card, and I can run two captures concurrently as independent processes
> putting output into two different files. I haven't tried running all four
> at once (though that's my long-term goal, along with another four audio
> channels from a USB capture device).
> However, I would like to be able to put the multiple streams into a single
> file. There are a couple of reasons for this, and if my expectations are
> misplaced, now's a great time to tell me. One is that I'd like the
> timecodes to be synchronized, another is that I'd prefer a single command
> to start everything, and end everything, at the same instant. This, I hope
> will reduce the complexity of synchronizing the channels in later editing.
> But I have no clue how to start with this. I tried simply adding more input
> channels to my input specifications:
> ffmpeg -f decklink -i 'DeckLink Quad HDMI Recorder (1)' -f decklink -i
> 'DeckLink Quad HDMI Recorder (4)'  -c:v copy -c:a copy -metadata
> title=DeckLinkCapture  capture.mov
> But all I got was a ton of buffer overruns, and a file that ffprobe said
> only contained one video stream.
> I believe that .mov can hold multiple streams, but I have not particular
> reason for using that file format, other than I often use it when I go with
> a prores compression. (I'm hoping that later in this project I might get
> enough CPU power to go that route, and reduce bandwidth and storage
> requirements to less insane levels)
> Can someone point me at a template for a command line that might do what I
> need? If the explanation or resources might help me understand the concepts
> better, that would be a bonus (and might result in my becoming a little
> more self-sufficient!)
> Cheers,
> Simon
> --
> Simon Roberts
> (303) 249 3613
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