Converting mkv, mpeg-2, anything from disc, to DnxHD or Prores using ffmpeg

Let’s suppose, for the sake of argument, that you’ve been asked by a director to cut his directing reel. He hands you a DVD and a Blu-ray and asks you to grab clips from them.

There are three problems here. The first is that you really should have been handed Prores or something editable from the get-go. But let’s assume you can’t get the media any other way (because often, you just can’t), and let’s assume that this is all considered fair-use (though current law makes that a bit muddy). We’re left with two technical problems:

  1. Rip: Getting the media off the disc and into a file, which may require circumventing copy protection mechanisms and encryption.
  2. Transcode: Converting the resulting file into something editable. Avid Media Composer won’t cut a .mkv file, and works with a limited range of video codecs. FCPX and Adobe Premiere Pro, despite their focus on working efficiently with many codecs, will still have trouble with some file formats. So this step is required for them too.

Rip

Regarding getting the clips off the disc, there are several applications out there for DVD, and only one that I know of for Blu-ray. From DVD, many people use a pretty fancy open-source tool that lets you pull selected ranges of video, and saves to mp4 (the software is designed to make files that play back on media devices, not for editorial purposes). If I’ve ever had to do this hypothetical task, I’ve avoided using this tool because I want the video to transfer from disc to file with no transcoding or lossy compression in between. So I’d have used this one tool which works for both DVD and Blu-ray. The result is a .mkv file which contains all the video and audio from the disc in its original codec.

So you’ve ripped the video from the disc and you’ve got an mkv file or files. You can play these in VLC Player to have a look at their contents to be sure you’ve got what you need. But none of the NLEs with which you edit can work with the files directly. Here’s how to convert them to dnxhd in order to be able to bring them into Media Composer. We’re going to use an awesome command-line tool called ffmpeg.

Install ffmpeg

At this point, I’m going to be giving instructions that relate to computers running Apple’s OS X. I’m sure it’s possible to do the next steps on a machine running Windows or Linux, but I’m not sure of the exact process. And we’re going to be using the Terminal, which you can find in /Applications/Utilities. You might as well open a Terminal window now.

There are a number of precompiled versions of ffmpeg floating around for download, but the only way to be sure you’re getting one with support for all the necessary formats built-in is to build it from source on your machine. To compile it, you’ll need Apple’s free development tool, Xcode, or at least the Xcode command line utilities. Download and install that from Apple. Then you’ll need to install ffmpeg and its dependencies, a task that is made pretty easy by a packaging system called ‘homebrew‘. If you’ve never set a password for your user account on OS X, you’ll need to do that first (the unix ‘passwd’ command, entered at the Terminal prompt, is a fast way to do this). It’s very easy to install homebrew, you just copy and paste one long command from homebrew’s web site into your Terminal window.

Once you’ve got Xcode and homebrew installed, you’re ready to install ffmpeg. I do so by pasting the following into the terminal window:

brew install ffmpeg --with-fdk-aac --with-ffplay --with-fontconfig --with-freetype --with-frei0r --with-libass --with-libbluray --with-libcaca --with-libquvi --with-libsoxr --with-libvidstab --with-libvo-aacenc --with-libvorbis --with-libvpx --with-opencore-amr --with-openjpeg --with-openssl --with-opus --with-rtmpdump --with-schroedinger --with-speex --with-theora --with-tools --with-x265

That should all be one long line. Hit return, and brew will start downloading tool after tool, occasionally prompting you, and eventually installing ffmpeg. This may take a while, depending on the speed of your computer and the speed of your net connection. A half-hour wouldn’t be out of the ordinary. But when it’s done you’ll have an amazing multimedia swiss army knife at your disposal. I use ffmpeg for nearly all of my transcodes, even to watermark and transcode for upload to video distribution platforms.

Transcode your files with ffmpeg

Now that ffmpeg is installed, you can transcode your mkv file into dnxhd with one line of commands entered at the Terminal prompt. Here it is:

ffmpeg -i inputfilename.mkv -vf "scale=1920:1080" -vcodec dnxhd -r 23.976 -b:v 36M -c:a pcm_s16le -ar 48000 -ac 2 outputfilename.mov

For command-line newbies, I should point out that spaces are used as a special character to separate commands and their arguments. So if there are any spaces in your filename, or in any directory along the way to your file, they need to be typed in a special way (“escaped” with a  backslash in front of it, like “\ “) so that the Unix shell knows to interpret them as a space and not as a separator. There are other special characters too. The safest way to type the filename is to let the Terminal do it for you — just type “ffmpeg -i ” (don’t type the quotes, but do type the space after the i) and then drag your input file right into the Terminal window. It’ll type the whole path to the file into the Terminal, with all spaces and special characters properly escaped. So for this command, I do:

ffmpeg -i drag_in_mkv_file -vf "scale=1920:1080" -vcodec dnxhd -r 23.976 -b:v 36M -c:a pcm_s16le -ar 48000 -ac 2 drag_in_mkv_file_and_then_edit_its_name_to_end_in_mov

Hit enter, and ffmpeg do its thing. It’ll take the video from that mkv file, uprez it to 1080p if necessary, and output it as a DNxHD36 23.98 quicktime file with stereo 16-bit 48Khz audio. If that matches your Media Composer project’s settings, the video will fast-import. Unfortunately I haven’t yet nailed down the exact audio settings, so that audio will just do a normal and not fast-import (which means some conversion is happening during the import).

If the file you’re converting isn’t 23.98p, change that part of the command line to the appropriate frame rate. You’ll likely also need to change the bitrate. There’s a list of bitrates to use for different frame rates of dnxhd here (scroll down to the dnxhd section).

You can also convert your mkv or other files to prores using ffmpeg. For our blu-ray mkv file, a line like this should work:

ffmpeg -i inputfilename.mkv -vcodec prores -profile 2 -pix_fmt yuv422p10le -acodec pcm_s16le outputfilename.mov

That’ll make a Prores422 file with 16-bit audio. You can also do other types of Prores by changing the number after “-profile” to 0 for proxy, 1 for LT, or 3 for 422HQ.

In summary

Yes you can pull clips from DVD or Blu-ray and convert them into editable media without an intermediate transcode to mp4 – by losslessly ripping to mkv and then converting to Avid DNxHD or Prores using ffmpeg.

And if you get heavier into the command-line, you’ll find that it makes complicated scripting and batch processing pretty easy to do. So having a good command-line conversion tool becomes very powerful.

3 Responses to 'Converting mkv, mpeg-2, anything from disc, to DnxHD or Prores using ffmpeg'

  1. zachnfine Says:

    Converting mkv, mpeg-2, anything from disc, to DnxHD or Prores using ffmpeg https://t.co/B5Thg21azY

  2. sethevans Says:

    RT @zachnfine: Converting mkv, mpeg-2, anything from disc, to DnxHD or Prores using ffmpeg https://t.co/B5Thg21azY

  3. Peter Gerry Says:

    Thanks for sharing this. There are a couple of movies that I would like to rip but I have not tried to yet.

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