ffmpeg command line for capturing (and recording) audio and video in 720p from decklink card using Windows 7 -


i trying capture audio , video blackmagic decklink capture card using windows 7 @ 720p, cant seem ffmpeg command line settings right.

ffmpeg -list_devices true -f dshow -i dummy

[dshow @ 02457a60] directshow video devices [dshow @ 02457a60]  "blackmagic wdm capture" [dshow @ 02457a60]  "decklink video capture" [dshow @ 02457a60] directshow audio devices [dshow @ 02457a60]  "decklink audio capture"

ffmpeg -list_options true -f dshow -i video="decklink video capture"

[dshow @ 03c2ea20] directshow video device options [dshow @ 03c2ea20]  pin "capture" [dshow @ 03c2ea20]   pixel_format=uyvy422  min s=720x486 fps=29.97 max s=720x486 fps=29.97 [dshow @ 03c2ea20]   pixel_format=uyvy422  min s=720x486 fps=23.976 max s=720x486 fps=23.976 [dshow @ 03c2ea20]   pixel_format=uyvy422  min s=720x576 fps=25 max s=720x576 fps=25 [dshow @ 03c2ea20]   pixel_format=uyvy422  min s=720x486 fps=59.9402 max s=720x486 fps=59.9402 [dshow @ 03c2ea20]   pixel_format=uyvy422  min s=720x576 fps=50 max s=720x576 fps=50 [dshow @ 03c2ea20]   pixel_format=uyvy422  min s=1920x1080 fps=23.976 max s=1920x1080 fps=23.976 [dshow @ 03c2ea20]   pixel_format=uyvy422  min s=1920x1080 fps=24 max s=1920x1080 fps=24 [dshow @ 03c2ea20]   pixel_format=uyvy422  min s=1920x1080 fps=25 max s=1920x1080 fps=25 [dshow @ 03c2ea20]   pixel_format=uyvy422  min s=1920x1080 fps=29.97 max s=1920x1080 fps=29.97 [dshow @ 03c2ea20]   pixel_format=uyvy422  min s=1920x1080 fps=30 max s=1920x1080 fps=30 [dshow @ 03c2ea20]   pixel_format=uyvy422  min s=1280x720 fps=50 max s=1280x720fps=50 [dshow @ 03c2ea20]   pixel_format=uyvy422  min s=1280x720 fps=59.9402 max s=1280x720 fps=59.9402 [dshow @ 03c2ea20]   pixel_format=uyvy422  min s=1280x720 fps=60.0002 max s=1280x720 fps=60.0002

ffmpeg -list_options true -f dshow -i audio="decklink audio capture"

[dshow @ 047fea20] directshow audio device options [dshow @ 047fea20]  pin "capture" [dshow @ 047fea20]   min ch=1 bits=16 rate= 48000 max ch=1 bits=16 rate= 48000 [dshow @ 047fea20]   min ch=2 bits=16 rate= 48000 max ch=2 bits=16 rate= 48000 [dshow @ 047fea20]   min ch=4 bits=16 rate= 48000 max ch=4 bits=16 rate= 48000 [dshow @ 047fea20]   min ch=6 bits=16 rate= 48000 max ch=6 bits=16 rate= 48000 [dshow @ 047fea20]   min ch=8 bits=16 rate= 48000 max ch=8 bits=16 rate= 48000 [dshow @ 047fea20]   min ch=10 bits=16 rate= 48000 max ch=10 bits=16 rate= 48000 [dshow @ 047fea20]   min ch=12 bits=16 rate= 48000 max ch=12 bits=16 rate= 48000 [dshow @ 047fea20]   min ch=16 bits=16 rate= 48000 max ch=16 bits=16 rate= 48000

this stream information current video/audio source, connected decklink card's hdmi port

stream #0:0: video: rawvideo (uyvy / 0x59565955), uyvy422(tv), 1280x720, 59.94 tbr, 10000k tbn, 59.94 tbc stream #0:1: audio: pcm_s16le, 48000 hz, stereo, s16, 1536 kb/s

ultimately need display video on screen. , simultaneously able start , stop recording, while preview keeps playing.

my idea use ffmpeg capture video , audio signal , transmit network stream (eg 127.0.0.1:6666). use vlc player display stream (the preview). , start and/or stop ffmpeg save same stream disk.

in mind works, no audio/video expert if more experience out, appreciate it.

update:

i have been able display video using ffplay, following command : 

ffplay -f dshow -video_size 1280x720 -rtbufsize 702000k -framerate 60 -i video="decklink video capture":audio="decklink audio capture" -threads 2

next step streaming can view stream (preview) vlc.

tried use command : 

ffmpeg -f dshow -video_size 1280x720 -rtbufsize 702000k -framerate 60 -i video="decklink video capture":audio="decklink audio capture" -threads 2 -f mpegts rtp://127.0.0.1:6666?pkt_size=188?buffer_size=65535

which not give errors, appears work. when try open stream in vlc following error :

sdp required: description in sdp format required receive rtp stream. note rtp:// uris cannot work dynamic rtp payload format (65).

after bit of reading seems should not streaming rtp:// rather udp://

command became : 

ffmpeg -f dshow -video_size 1280x720 -rtbufsize 702000k -framerate 60 -i video="decklink video capture":audio="decklink audio capture" -threads 2 -f mpegts udp://127.0.0.1:6666?pkt_size=188?buffer_size=65535

and when try open in vlc no error, no warning, no video.

time more reading.

finally got working. setup has running on single machine.

for taking video , serving via udp use following command : 

ffmpeg -f dshow -video_size 1280x720 -rtbufsize 702000k -framerate 60 -i video="decklink video capture":audio="decklink audio capture" -r 30 -threads 4 -vcodec libx264 -crf 0 -preset ultrafast -f mpegts "udp://239.255.12.42:6666"
  • the "-f dshow" tells ffmpeg need use direct show.
  • "-video_size 1280x720" sets source size, since using 720p60 source, it.
  • "rtbufsize 702000k" important since without realtime buffer full in matter of seconds.
  • "-framerate 60" tells ffmpeg source using 60fps.
  • the option: video="decklink video capture":audio="decklink audio capture" tells ffmpeg use device input, specifying them in fashion, lag between audio , video substantially less (and/or gone).
  • "-r 30" forces output 30fps instead of 60fps in source.
  • "-threads 4" think, use 4 threads.
  • "-vcodec libx264" encodes source stream h264 while broadcasting.
  • "-crf 0" sets "constant rate factor" (quantizer scale) 0, meaning lossless.
  • "-preset ultrafast" means dont have patience, use little compression possible. causes high bitrate, that's fine purpose.
  • "-f mpegts" option tells ffmpeg use mpeg-ts packets, "force" ffmpeg use constant bitrate mpeg format, since mpeg variable bitrate.
  • finally option "udp://239.255.12.42:6666" specifies want broadcast stream multicast address 239.255.12.42 using port 6666 on udp. reason chose use multicast address here because need display stream (preview) , record @ same time, least processing possible. prevents me having copy audio , video stream 2 different network addresses.

for capturing video using vlc player, open following network streaming address : 

udp://@239.255.12.42:6666

finally recording stream spawn new process , issue following command : 

ffmpeg -y -threads 4 -i udp://239.255.12.42:6666 -map 0 -acodec copy -vcodec copy output.mkv
  • the "-y" option overwriting file if exists without questions.
  • the "-threads 4" option think, uses 4 threads.
  • the "-i udp://239.255.12.42:6666" connects stream broadcasting.
  • the "-map 0" tells ffmpeg need streams (both video , audio).
  • the "-acodec copy" , "-vcodec copy" there ensure streams taken is, instead of doing compression/transcoding.

the thing left (which work in progress atm) creating c# gui this. basic workflow spawn stream process when form loads. use vlc com+ control display video in application.

then when record button pushed, spawn process record , stop process end recording.

i stop stream when start record, makes recording/detection go more smoothly. if stream stays on , start recording take time before recording process can "tune in" stream. stopping stream, starting recording (which nothing until stream on) , starting stream again, recording pickup first frame without problems.

this small delay/flicker totally acceptable purposes.


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