Make sure Windows Media Player is installed Many apps use the Windows Decoder to avoid licensing fees.

Older versions required QuickTime.

I just ran into this issue too - can't open an m4a file that was sent to me by a friend who wanted me to inspect the sound levels. I can play the m4a audio in VLC player without issue, but I need to inspect it and can't open the file in SF 13 Pro. I have tried changing the file extension to mp4 and I already have Windows Media Player installed, but it didn't make any difference.

As for installing QuickTime, I'm hoping that's not needed. I tried to do so but got a "cab" issue when the exe file started to install. If I google the QT install error, people are basically are basically saying this:

Users shouldn’t need QuickTime on Windows 10 at all.

Applications that want to make use of QuickTime APIs should have updated to different technology many years ago, when support ended.

Codec support (H.264, AAC) that QuickTime might have added previously, has now been added to Windows without the need for QuickTime.

So why can't I open this file in SF 13 Pro that VLC plays perfectly? And advice would be appreciated.

M4a files normally use the AAC audio codec, but it could be something else. Post the file's attributes using MediaInfo, You could also try changing the file's extension to <.mp4> .

I did try changing the extension, but it didn't help. Here are the MediaInfo attributes:

General
Complete name                     Test Track Normalizing L R Channels.m4a
Format                                   : MPEG-4
Format profile                           : Apple audio with iTunes info
Codec ID                                 : M4A  (M4A /isom/mp42)
File size                                : 771 KiB
Duration                                 : 54 s 982 ms
Overall bit rate mode                    : Constant
Overall bit rate                         : 115 kb/s
Encoded date                             : UTC 2020-08-29 04:24:51
Tagged date                              : UTC 2020-08-29 04:24:52

Audio
ID                                       : 1
Format                                   : AAC LC
Format/Info                              : Advanced Audio Codec Low Complexity
Codec ID                                 : mp4a-40-2
Duration                                 : 54 s 982 ms
Source duration                          : 55 s 31 ms
Bit rate mode                            : Constant
Bit rate                                 : 112 kb/s
Channel(s)                               : 2 channels
Channel layout                           : L R
Sampling rate                            : 44.1 kHz
Frame rate                               : 43.066 FPS (1024 SPF)
Compression mode                         : Lossy
Stream size                              : 761 KiB (99%)
Source stream size                       : 761 KiB (99%)
Title                                    : Core Media Audio
Encoded date                             : UTC 2020-08-29 04:24:51
Tagged date                              : UTC 2020-08-29 04:24:52

Try changing file extension to <.raw>

Otherwise a work around is to convert the M4a to a PCM format in another app or use an online transcoder (Zamzar for instance)

Thanks for the advice. Changing it to .raw got SF13 to ask me some additional questions that I didn't quite know how to answer, and when I finally got it to open it was nothing but static noise. I will use Zamzar for now, since I'm just taking a peek at a small file for a friend, but I will have to ask him to convert his projects to something else in the future. I was just surprised because I'm used to Sound Forge opening everything successfully. Cheers!

Prior to the latest versions of Vegas, a QT app needed to be installed to open AAC audio files in Vegas and SF (.mov, .mp4 and m4a). I installed the Quicktime Alternative codec on all my PCs and never had issues opening or encoding.

VEGAS Pro (<= 17), Sound Forge Pro (<= 13), and ACID Pro all have this issue.

I have just encountered the very same issue. I am using Sound Forge Pro, last release. Support's had me install Quicktime Alternative, but it did not solve. It lets me 'open' the file (an .m4a Atmos file), but all I get is an empty, two channels thing.

I'm waiting for Support's next reply. How's it possible that, after YEARS, this hasn't been fixed yet?

@GiorgioV Is the file copy protected? Then I don't think that Sound Forge can open it.

Atmos licenses for encoding/decoding are pretty pricey, to my knowledge multiple hundreds of Dollars per year.

Maybe this tool can help. https://www.quadraphonicquad.com/forums/threads/music-media-helper-tools-for-multichannel-audio-music-videos.22693/