Lazyweb, earn your keep:

How do I get video out of a BlackMagic SDI-to-HDMI 4K MiniConverter using ffmpeg on MacOS?

I installed it like this:

port install ffmpeg +nonfree +librtmp +libdc1394

I gather that the following incantation should list available input devices, but it freaks out halfway through:

ffmpeg -list_devices true -f avfoundation -i dummy

ffmpeg version 2.3.3 Copyright (c) 2000-2014 the FFmpeg developers
built on Aug 21 2014 20:56:05 with Apple clang version 4.1 (tags/Apple/clang-421.11.66) (based on LLVM 3.1svn)
configuration: --prefix=/opt/local --enable-swscale --enable-avfilter --enable-avresample --enable-libmp3lame --enable-libvorbis --enable-libopus --enable-libtheora --enable-libschroedinger --enable-libopenjpeg --enable-libmodplug --enable-libvpx --enable-libspeex --enable-libass --enable-libbluray --enable-gnutls --enable-fontconfig --enable-libfreetype --enable-libfribidi --disable-indev=jack --disable-outdev=xv --mandir=/opt/local/share/man --enable-shared --enable-pthreads --cc=/usr/bin/clang --enable-vda --arch=x86_64 --enable-yasm --enable-libdc1394 --enable-librtmp --enable-gpl --enable-postproc --enable-libx264 --enable-libxvid --enable-nonfree --enable-libfdk-aac --enable-libfaac
libavutil 52. 92.100 / 52. 92.100
libavcodec 55. 69.100 / 55. 69.100
libavformat 55. 48.100 / 55. 48.100
libavdevice 55. 13.102 / 55. 13.102
libavfilter 4. 11.100 / 4. 11.100
libavresample 1. 3. 0 / 1. 3. 0
libswscale 2. 6.100 / 2. 6.100
libswresample 0. 19.100 / 0. 19.100
libpostproc 52. 3.100 / 52. 3.100
[AVFoundation input device @ 0x7f935ac2d3e0] AVFoundation video devices:
[AVFoundation input device @ 0x7f935ac2d3e0] [0] Blackmagic
dummy: Input/output error
Exit 1

My reading of various cargo-cult droppings suggested that my command might look something like:

cmd="ffmpeg -f avfoundation"
cmd="$cmd -i video=Blackmagic"          # device
cmd="$cmd -video_size 1280x720"         # input video size
cmd="$cmd -framerate 60"                # input video frame rate
cmd="$cmd -r 15"                        # output video fps
cmd="$cmd -g 30"                        # output motion estimation?
cmd="$cmd -maxrate 350k"                # output video rate
cmd="$cmd -bufsize 700k"                # output video rate
#cmd="$cmd  -rtbufsize 702000k"         # output video rate?
cmd="$cmd -vf scale=640:-1,format=yuv420p"     # output video size
cmd="$cmd -threads 4"                   # tune this?
cmd="$cmd -acodec libmp3lame"           # output audio codec
cmd="$cmd -ac 2"                        # output audio channels
cmd="$cmd -b:a 96k"                     # output audio bps
cmd="$cmd -ar 44100"                    # output audio Hz
cmd="$cmd -vcodec libx264"              # output video codec
cmd="$cmd -crf 23"                      # constant rate factor. 0 = lossless, 18 good, 23 default, 51 worst
cmd="$cmd -preset ultrafast"            # little compression, high bitrate
cmd="$cmd -f mpegts"                    # MPEG-TS packets, CBR MPEG
cmd="$cmd -f flv"
cmd="$cmd rtmp://a.rtmp.youtube.com/live2/[REDACTED]"

But that fails:

[avfoundation @ 0x7f8d3b82cc00] Failed to create AV capture input device: Cannot Use Blackmagic
Blackmagic: Input/output error

Also, how do I tell it to take video from Blackmagic but encode silence as audio? Not "no audio stream", but rather, "there is an audio stream and it is silent"?

Also, how do I tell it to take video from Blackmagic but audio from the Mac's built-in analog line-in jack?

Previously, previously, previously.