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Create a 16-channel Audio Stream?

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Jason Douglas
Create a 16-channel Audio Stream?
on Feb 1, 2014 at 7:10:48 am

Could someone shed some light on creating a video file containing a stereo/2-channel audio stream into a new file with 16-channel stream? The destination is a DNxHD with pcm_s24le audio. I have tried every commandline argument I can find and they are either outdated or error out instead of creating additional channels... I was able to do it somewhat with ffmbc, but it would crash with %80 of my files.

I am attempting to author files for playback on a hyperdeck. I have managed to create uncompressed v210 files that playback fine. I am trying to DNxHD to reduce file size and increase the length of clips I can fit on 256Gig SSDs... the files I have created play video fine, but I definitely need to match the audio format to have a hope for it working.

I have been using FFmpeg with much success lately, but I have found plenty of reference on splitting a single 16-channel stream into seperate streams, but not how to create a 16-channel stream. Ideally, 0=0, 1=1, 2-15 muted... Thank you in advance for any insight offered!


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stephen dixon
Re: Create a 16-channel Audio Stream?
on Feb 2, 2014 at 10:45:10 am

I think you may need to do it in two passes. First create a file with all the audio as separate streams, and then use that as the input to the next pass, where you can use the amerge filter to merge them into a single multi-channel stream.

http://ffmpeg.org/ffmpeg-filters.html#amerge and https://trac.ffmpeg.org/wiki/AudioChannelManipulation might be helpful.

Stephen Dixon
Editor, Animator, Motionographer
Museum Victoria


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Lou Logan
Re: Create a 16-channel Audio Stream?
on Feb 2, 2014 at 7:55:04 pm

[Jason Douglas] "how to create a 16-channel stream. Ideally, 0=0, 1=1, 2-15 muted..."

I don't really understand. Why do you need 16-channels? Where is the audio data coming from for the 2-15 channels? Or do you just want to generate silent audio?


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Jason Douglas
Re: Create a 16-channel Audio Stream?
on Feb 4, 2014 at 3:50:54 am

I will try the multi-pass.

In order for the Blackmagic Hyperdeck to recognize a clip, it must mee the exact standard for playback. If it isn't a 16-channel 24-bit LPCM stream, it won't play it... Thanks Blackmagic...


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Jason Douglas
Re: Create a 16-channel Audio Stream?
on Feb 4, 2014 at 6:43:25 am

I was able to create a 16-channel stream with:
ffmpeg -i wildlife.wmv -c:v dnxhd -b:v 185M -r 29.97 -s 1920x1080 -flags +ildct -filter_complex "[0:a][0:a][0:a][0:a][0:a][0:a][0:a][0:a] amerge=inputs=8" -c:a pcm_s24le -ar 48k output.mov

The ffprobe of the resulting file shows: 16 Channels (FL+FR+FC+LFE+BL+BR+FLC+FRC+BC+SL+SR+TC+TFL+TFC+TFR+TBL)... Is it possible to assign a channel map of 16 mono channels or no map at all?


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Reuben Martin
Re: Create a 16-channel Audio Stream?
on Feb 5, 2014 at 3:22:51 am

I believe the channel mapping is assumed (although I may be wrong).

Are you sure the Hyperdeck needs a single audio stream with 16 channels? Most hardware I've run into uses 16 separate audio streams with a single channel each.


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Jason Douglas
Re: Create a 16-channel Audio Stream?
on Feb 5, 2014 at 4:12:17 am

I have recorded test files in the various formats supported by the hyperdeck. Prores has been a block wall. Black magic uses their own implementation that makes it impossible to author correct files with ffmpeg.

DNxHD in mxf wrapper uses a 24 bit linear pcm 16-channel stream. This is what I am trying to create.

I know DNxHD in an move wrapper creates 3 files: 1 video and 2 audio. I haven't analyzed those files yet, but will tonight as an alternative.


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