Ubuntu Multimedia :: Capture The Video Using The Command Line?

I wanted to share this nifty technique I came across for capturing video using the command line. The problem: I have a bunch of old VHS tapes (remember those...?) and need to get them digitized. I have a VCR, and a Dazzle Hollywood DV Bridge which captures video to DV over Firewire (IEEE1394). I first tried using Final Cut Pro, but it wouldn't capture, perhaps because it expects a controllable DV camera, and the Dazzle isn't a DVC device. I then tried my other favorite video editing app, Kdenlive, but it seemed to have the same problem.

I took a quick stab at the other common editors in the repositories (Kino, Openshot, etc.), but no luck with any of them. Then I remembered the dvgrab command, and gave that a shot and it worked, giving me a nice .dv file. However, DV makes pretty big files, which I wanted to compress down to something more manageable. Since I was going to be digitizing hours and hours of tapes, it would be great if I could compress while capturing. A little more googling and I had the answer - you can pipe dvgrab directly into ffmpeg! Here's the command:

Code:

dvgrab -format dv1 - | ffmpeg -f dv -i - -b 2000k -ab 512k -y output.mov

the first part starts the capture, in DV1 format, and outputs it to a pipe file. usually you give dvgrab a filename, like

Code:

dvgrab -format dv1 capture.dv

the second part does the encoding:

-f dv: use DV format
-i -: input from the pipe
-b 2000k: video encoding bitrate of 2000k/sec, high quality
-ab 512k: audio encoding bitrate
-y: overwrite file if it exists

I didn't set the codec explicitly, for Quicktime it defaults to MPEG4. This worked great, capturing a 2-hour tape into a high-quality quicktime around 2GB. But I also wanted to be able to view the capture while it was going. Since I left the field monitors and audio splitters at the office, I had to figure out how to do this in software. Turns out that the "tee" command does exactly what I needed - the shell never ceases to amaze! Here's the full command:

Code:

dvgrab -format dv1 - | tee >(ffmpeg -f dv -i - -b 2000k -ab 512k output.mov) >(playdv --disable-audio --no-mmap)

tee uses the

Code:

>(command)

syntax to pipe simultaneously to multiple processes. The only thing that didn't work was audio playback, which was choppy and introduced errors in the capture file. I think a little tweaking with the capture rates could fix that.