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Export .MXF with stereo (dual channel) audio track

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Guillaume Bringard
Export .MXF with stereo (dual channel) audio track
on Jul 4, 2018 at 6:16:14 am

Hello

For a broadcaster, I'm trying to deliver an MXF OP1a 1080i25 file, with video in AVC-Intra 100 (no problems here) and two stereo audio tracks (from two different stereo audio mix, French version and International version).
I must specifically output each one of those two stereo mix on one dual-channels tracks, so I must have two dual-channel (stereo) tracks, and not 4 single (mono) tracks.

Using Resolve 14, here is what I did :
1/ the source audio mix are stereo .WAV files, properly defined as such in the Clip Attributes of the Media Pool
2/ the timeline tracks are stereo (2.0) tracks, the WAV files do playback properly in stereo
3/ in Fairlight, I create two stereo main buses, and I assign track 1 to bus 1, and track 2 to bus 2. The Mixer then properly displays two stereo master buses, on each the two stereo audio files play properly : the first audio stereo source file on the first main stereo bus, the second audio stereo source file on the second stereo main bus.
So far, so good.

But when delivering in .MXF, no matter what audio setup I select (either the two stereo Main Fairlight buses output, or the stereo timeline tracks output), the audio in the resulting MXF are always flagged (in Media Info, for example, and by the broadcaster's QC tool) as 4 single mono channel tracks.

The same audio setup output in Quicktime .MOV does work : I do get two dual-channel stereo tracks.
But not in .MXF.

Has anyone ever managed to output stereo dual-channel tracks in an MXF from Resolve ? If so, what do I do wrong ?

Thanks !


Guillaume


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John Pale
Re: Export .MXF with stereo (dual channel) audio track
on Jul 5, 2018 at 2:54:26 am

MXF doesn’t support that audio configuration. Only Quicktime does.

Please check with your broadcaster and ask how they want to proceed.


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Guillaume Bringard
Re: Export .MXF with stereo (dual channel) audio track
on Jul 5, 2018 at 8:01:51 am

Hello

I did check with my broadcaster, he sent me an MXF sample of a file validated on their side, it definitely has dual (stereo) channels tracks when opened in Media Info :




What I get from Resolve is two single-channeled (mono) tracks :



And yes, you're right, it does work properly when delivering a MOV file from Resolve :



But not when delivering and MXF...


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Guillaume Bringard
Re: Export .MXF with stereo (dual channel) audio track
on Jul 5, 2018 at 4:24:34 pm

In the meantime, I found a workaround with FFMPEG :

1/ I export from Resolve the video silent (without audio) as an .MXF OP1a AVC-Intra 100 1080i25 (every flavor I need)

2/ I export from Resolve the audio as stereo .WAV (48 Khz 24 bits)

3/ I rewrap without converting/re-compressing via FFMPEG :
ffmpeg -i VideoSilentFile.MXF -i AudioStereoWaveFile.wav -map 0:0 -map 1:a -vcodec copy -acodec copy VideoWithStereoAudio.MXF


And voilà : an .MXF file with only one stereo audio track containing two audio channels :-)


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John Pale
Re: Export .MXF with stereo (dual channel) audio track
on Jul 5, 2018 at 7:06:55 pm

I missed that you are trying to make an AVC Intra MXF OP1a file. The limitation I mentioned applies to XDCAM HD based MXF OP1a files. You can, in fact make such files with stereo tracks using Adobe Media Encoder.

I see in your MediaInfo screen capture that your encode uses Sony libraries....are you sure you are exporting an AVCIntra and not a Sony XDCAM MXF file?


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Guillaume Bringard
Re: Export .MXF with stereo (dual channel) audio track
on Jul 5, 2018 at 9:34:47 pm

Yes, I'm fairly certain I'm exporting an AVC-Intra video compression 😉


But maybe you're onto something : since Da Vinci Resolve seems to rely on this "Sony MXF Development Kit" pointed out by Media Info, maybe the limitation of the mono-channeled tracks lies in there, historically inherited from the XDCAM ages...


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