The venerable FFmpeg audio/video tool can now package its output in Avid Op-Atom format directly, without always needing to have its output wrapped by the raw2bmx tool. This method is very fast and, crucially, can be used on any computer; not just the machine with your Avid licence. However, certain features of the Avid Op-Atom MXF wrapper are either not yet tested, or not available. For these features, I still advise using the bmxlib suite.
The advantage of this method is that video and audio data is very quickly imported into your Avid, at the full rate that the FFmpeg encoder can manage. Furthermore, your Avid will be using its native formats (e.g. DNxHD), rather than converting, say, XAVC on-the-fly with the AMA functions. The disadvantage is that metadata is quite messy, and lacking certain elements altogether, until I’ve figured out the full MXF Op-Atom metadata tags. Particularly, audio and video tracks are not linked into a single multi-track clip in an Avid bin: you must synchronise them yourself.
So, in this article, I will show you how to take video and/or audio from any format that FFmpeg will read, and output immediately MXF files in Avid-friendly codecs that Avid Media Composer’s “Media Tool” will pick up for you.
This post shows my earliest tests. I have not yet fully explored how to link files, or add other attributes, that raw2bmx adds or, indeed, Avid’s own import and capture tools add. However, the advantage of not using raw2bmx is a much faster import process.
Here, we start with a file of any format with a mono soundtrack, and output Avid DNxHD files at a resolution of 1280×720 and a bit-rate of 90Mbit/s, straight into the Avid MediaFiles directory, and ready for editing. This workflow assumes the frame-rate is for UK television, at 25fps, progressive encoding. I have not attempted to detect the number of audio channels in use, and therefore they are not encoded separately. This is, however, easy to achieve by using FFmpeg’s “asplit” audio filter and is detailed on the FFmpeg website.
ffmpeg -i "MY_CLIP.f4v" -vf scale=1280:720:lanczos -an -metadata project="MY PROJECT" -metadata material_package_name="MY CLIP" -b:v 90M -f mxf_opatom "M:\Avid MediaFiles\MXF\1\MY_CLIP_v1.mxf" -vn -metadata project="MY PROJECT" -ac 1 -ar 48000 -metadata material_package_name="MY CLIP" -f mxf_opatom "M:\Avid MediaFiles\MXF\1\MY_CLIP_a1.mxf"
Here is a break-down of that command line:
-i "MY_CLIP.f4v"
Here is the incoming clip.
-vf scale=1280:720:lanczos
We start with producing an output video MXF. Here, we ensure that the video is resized to the particular flavour of HD we’re editing in. In this case, we’re using 720p, and resizing using the algorithm I consider to be the best.
-an
The video output can contain only one track: video, in this case. This command instructs that the output must contain no audio. (Literally: “audio, none”)
-metadata project="MY PROJECT"
Here, we embed into the MXF metadata a value for “project”. This corresponds to your Avid project name. It is true that, upon analysing Avid’s own MXF files, the project name is contained within the metadata tag “project_name”, but my shorter tag appears also to work.
-metadata material_package_name="MY CLIP"
This is the name of your clip, as it will appear in your Avid bins and in the Media Tool.
-b:v 90M
Here, set the bit-rate. Using FFmpeg’s built-in DNxHD encoder, you can choose from several bit-rates, which FFmpeg’s error messages will be happy to tell you about if you set this wrongly. We don’t explicitly set the encoder itself, because FFmpeg does that for you: its default for this muxer is DNxHD.
-f mxf_opatom
This explicitly instructs FFmpeg to wrap your data in an Op-Atom MXF wrapper, ready for your Avid Media Composer to use.
"M:\Avid MediaFiles\MXF\1\MY_CLIP_v1.mxf"
Finally, for the video file, here is the output file. In this case, I’m putting it straight into Avid’s media file storage area on my ‘M’ drive, for media. There is a "_v1" suffix so that the file is marked as a video file, for my own ease of comprehension.
-vn
After the video output file is named, we start listing the options for encoding the audio file. This first option instructs FFmpeg to produce an audio-only MXF file, without a video track. (Literally: “video, none”)
-metadata project="MY PROJECT"
As with the video file, we embed into the metadata the name of the Avid project that needs this file.
-metadata material_package_name="MY CLIP"
As above, this is the clip name as it will appear in your Avid bins or Media Tool.
-ac 1
This is a quick-and-dirty kludge to mix down all the incoming audio tracks to a single track. In real life, you’ll want to use FFmpeg’s filter “asplit” to handle each incoming audio track separately. At the moment, this command line produces only a single audio file, mixing together all incoming tracks.
-ar 48000
With this command, we convert the sample-rate of the incoming audio to the standard sampling rate for television: 48,000 samples per second. Avid can, of course, convert sample rates on-the-fly while editing, but it is better to perform this work at the import stage to give Avid less to do when editing. Again, the codec itself (pcm_s16le, meaning linear PCM, 16-bit, little-endian) is not explicitly specified because FFmpeg sets this as the default for Avid import.
-f mxf_opatom
As before, this explicitly instructs FFmpeg to wrap your data in an Op-Atom MXF wrapper, ready for your Avid Media Composer to use.
"M:\Avid MediaFiles\MXF\1\MY_CLIP_a1.mxf"
Here is the filename for the audio output. In this example, I have placed it in the same directory as the video output created earlier in this command line. It is suffixed with "_a1" for my own ease of comprehension.
There are additional options associated with this FFmpeg muxer, which are listed here. I have not experimented with these, but can see that the -mxf_audio_edit_rate might need to be adjusted for non-European television or film work e.g. 30000/1001 for American television work, or 24 or 24000/1001 for 24fps film work. Also, you would probably want to set the -signal_standard bt601 or -signal_standard 1 for standard definition television work.
Muxer mxf_opatom [MXF (Material eXchange Format) Operational Pattern Atom]:
- Common extensions:
- mxf
- Mime type:
- application/mxf.
- Default video codec:
- dnxhd.
- Default audio codec:
- pcm_s16le.
MXF-OPAtom muxer AVOptions:
- bt601
- ITU-R BT.601 and BT.656, also SMPTE 125M (525 and 625 line interlaced)
- bt1358
- ITU-R BT.1358 and ITU-R BT.799-3, also SMPTE 293M (525 and 625 line progressive)
- smpte347m
- SMPTE 347M (540 Mbps mappings)
- smpte274m
- SMPTE 274M (1125 line)
- smpte296m
- SMPTE 296M (750 line progressive)
- smpte349m
- SMPTE 349M (1485 Mbps mappings)
- smpte428
- SMPTE 428-1 DCDM