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Why does Microsoft Office recommend the use of "m4a files encoded with AAC audio" for PowerPoint audio?

Posted on 2016-09-13
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Last Modified: 2016-09-14
So I’m sitting here working on a video project which the client has specified must be done in PowerPoint. The script is done and the voice over (VO) artist asks me “what format do you want the audio files in?”. I initially say “MP3” but after checking, I find this Microsoft Office article that recommends .m4a with AAC:

https://support.office.com/en-gb/article/Video-and-audio-file-formats-supported-in-PowerPoint-d8b12450-26db-4c7b-a5c1-593d3418fb59?ui=en-US&rs=en-GB&ad=GB&fromAR=1

The VO artists says “are you sure? I’ve never been asked for that before” and I start do doubt the logic behind the recommendation.

Does anyone know why Microsoft are making this recommendation? Will there be any “nasties” uncovered if I use MP3? And if they go to the trouble of making a recommendation, why not specify recommended encoding parameters such as sampling and bit rates e.g. 16 bit @ 48kHz?
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Question by:Jamie Garroch
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by:Rgonzo1971
Rgonzo1971 earned 150 total points
ID: 41795623
Hi,

m4a stands for Mpeg-4: so a better sound and a smaller file then mp3

https://en.wikipedia.org/wiki/MPEG-4_Part_14

Regards
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Guy Hengel [angelIII / a3] earned 350 total points
ID: 41795624
this is the key info:
>for the best video playback experience<
the format suggested (M4A is MP4, in short), which is audio + video

you want to put only audio, right? in that case, stay with MP3, which is still perfectly supported format
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by:Jamie Garroch
ID: 41795738
Having read both of these answers (thank you), I think Guy's comment points to the reason for the MSFT recommendation. If PowerPoint is being used to export a presentation to a video format, then the output format is most likely to be selected as MP4 (the only other option is WMV). That means PowerPoint needs to transcode all embedded non-M4a standalone audio files during that process and hence the user could see a slower export time if audio files are not using the M4a format. That would make sense to me but is it correct?

Reverting to the recommended sampling rate and size, if I export a test deck to MP4 and examine the audio properties, I can see that PowerPoint is using the following:

Channels : 2
Sample Rate : 44.1kHz
Sample Size : 16 bit
Codec : MPEG2/4

So can I assume this is the recommended/optimised encoding format for standalone audio?
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Expert Comment

by:Guy Hengel [angelIII / a3]
ID: 41796076
yes
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