Incorrect AAC Opening

[alexius]

Audacity v1.3.13-beta, Mac OS X v10.6.8

Attempting to open an MP4 file with Audacity (without ffmpeg) yields incorrect parameters. The file is

44.1kHz, stereo, 16-bit
AAC, 48kbps
profile: High-Efficiency v2
encoder: Lavf52.94.0

Audacity opens it as mono, 22kHz. The only difference between "open" and "import" is that, with the latter, Audacity complains that ffmpeg libraries cannot be found (I did not install them), but goes on to open it anyway.

(Other apps, eg, iTunes, recognise that the file is 44.1kHz, stereo, rather than 22.05kHz, mono.)

[Gale Andrews]

Audacity v1.3.13-beta, Mac OS X v10.6.8

Attempting to open an MP4 file with Audacity (without ffmpeg) yields incorrect parameters. The file is

44.1kHz, stereo, 16-bit
AAC, 48kbps
profile: High-Efficiency v2
encoder: Lavf52.94.0

Audacity opens it as mono, 22kHz. The only difference between "open" and "import" is that, with the latter, Audacity complains that ffmpeg libraries cannot be found (I did not install them), but goes on to open it anyway.

(Other apps, eg, iTunes, recognise that the file is 44.1kHz, stereo, rather than 22.05kHz, mono.)

Thanks for the report. Audacity uses QuickTime to import AAC on Mac if FFmpeg is not present.

I am surprised if this is a general problem because I do not recall it before.

Is it possible to post the file to yousendit, sendspace, megaupload or some other file transfer service?

Please also open Help > Show Log, and use Log > Save to save the log. That may give a little diagnostic information. You can upload the log as an attachment, underneath where you post messages.



Gale

[alexius]

Audacity uses QuickTime to import AAC on Mac if FFmpeg is not present.

Thanks for the reply. Sound Studio 2 also uses QuickTime, but it opens the file correctly (stereo, 44.1kHz).

Is it possible to post the file to yousendit, sendspace, megaupload or some other file transfer service?

Unfortunately, no. I'm currently in a country where the services of this type that I'm aware of are blocked.

Please also open Help > Show Log

When I launch it, the log records Audacity's failure to find FFmpeg libraries. When I open the respective file, the log says,

11:30:17: File name is <path_to_file>
11:30:17: Mime type is *
11:30:17: Opening with libsndfile
11:30:17: Opening with liboggvorbis
11:30:17: Opening with libflac
11:30:17: Opening with lof
11:30:17: Opening with libav
11:30:17: Opening with quicktime
11:30:17: Open(<path_to_file>) succeeded

I can attach the whole log, if that's really necessary.

[alexius]

OK, here's some additional info:

(1) Just for fun, I tried the file on a few other apps. Amadeus Pro, Peak 5, Max, and (surprise, surprise) QuickTime Player all opened it just like Audacity (mono, 22.05kHz). Sound Studio 4 doesn't open it, and Fission 1.6 opens it, but doesn't seem to find any audio data in it. iTunes and MediaHuman Audio Converter are the only ones which open it with the correct parameters. (I use MHAC for audio format conversion.) Sound Studio 2 also opens it correctly with QuickTime, but it puts up a dialogue to choose sample rate, bit depth, and channels. The correct values are selected, but I don't know if that's the default anyway.

(2) I tried another MP4 file, and this one was opened correctly by Audacity, as well as the other apps.

44.1kHz, stereo, 16-bit
AAC, 128kbps
profile: Low Complexity
encoder: Lavf52.94.0

So it looks like the problem might be with the bit rate or the profile or QuickTime -- perhaps QuickTime doesn't provide the right data to apps which rely on it.

[kozikowski]

Which QuickTime have you got? Snow Leopard installs the all-but useless QuickTime 10. QT10 is Apple's idea to simplify QuickTime and make it a Simple Player. Everybody hated it.

I installed the fully featured QuickTime 7 as a Utility and use that for everything.

Do you have Finder set to show you all file extensions?

Finder > Preferences > Advanced > [X] Show File Extensions.

It does bother me you keep calling it MP4. When QuickTime manages an AAC file, it comes out M4A. Yet another reason to inspect the file extensions. MP4 could be a video file.

Koz

[alexius]

Which QuickTime have you got?

I suggest consulting Apple's overview of QuickTime

http://developer.apple.com/library/mac/ ... rview.html

as well as this chapter of John Siracusa's review in Ars

http://arstechnica.com/apple/reviews/20 ... 10-6.ars/6

It does bother me you keep calling it MP4.

I'm so sorry you are bothered. Perhaps consulting

http://en.wikipedia.org/wiki/MPEG-4_Par ... extensions

will allay to some small extent the distress.

MP4 could be a video file

Indeed it could, just as .m4a (which is simply another filename extension for the same container format) could be an Apple Lossless-encoded audio file. But, in this instance, it is neither; rather, it is an AAC-encoded file, as I indicated in the OP.

[Gale Andrews]

the problem might be with the bit rate or the profile or QuickTime -- perhaps QuickTime doesn't provide the right data to apps which rely on it.

Certainly HE is less compatible than LC. Audacity on Windows (using FFmpeg) imports an HE encoded AAC file created by iTunes OK. You could try encoding to HE in iTunes ("Import Settings" in the Preferences) and see if that fares better than the file you had the issue with.



Gale

[alexius]

You could try encoding to HE in iTunes ("Import Settings" in the Preferences) and see if that fares better than the file you had the issue with.

No problem with iTunes and HE; but the problem file was not encoded with iTunes and AFAICT used a different profile.

Anyway, I normally use for this task MHAC, which never had a problem -- perhaps it's not using QuickTime. I was actually testing Sound Studio 4.2 (IMHO not as good as its venerable ancestor). As it couldn't open the file, I also tried Audacity, with the results described above, and I thought you guys might wish to know about it. But since other apps which rely on QuickTime show the same problem, the issue cannot be with Audacity. It must be with the encoder, or the profile, or QuickTime itself.

[kozikowski]

It's your opinion that Mac Audacity should be able to open and export AAC files just fine because it uses Quicktime Libraries?

Koz

[alexius]

Since the line

encoder: Lavf52.94.0

suggests that the file was encoded with ffmpeg, I downloaded and installed the ffmpeg 0.6.2 libraries as instructed

http://manual.audacityteam.org/man/FAQ: ... tallffmpeg

and tried again. This time, Audacity opened with the correct sample rate (44.1), but the channels were still wrong -- mono, instead of stereo. I also tried a few other files from the same source, and the results were consistent, so it was not a problem with one particular file.

Here's an extract from Audacity's log:

All symbols loaded successfully. Initializing the library.
Retrieving FFmpeg library version numbers:
AVCodec version 0x344802 - 52.72.2 (built against 0x344802 - 52.72.2)
AVFormat version 0x344002 - 52.64.2 (built against 0x344002 - 52.64.2)
AVUtil version 0x320f01 - 50.15.1 (built against 0x320f01 - 50.15.1)
FFmpeg libraries loaded successfully.
File name is <path_to_file>
Mime type is *
Opening with libsndfile
Opening with liboggvorbis
Opening with libflac
Opening with lof
Opening with libav
Open(<path_to_file>) succeeded

So perhaps the problem is that Audacity uses an older library (52.64.2) which doesn't understand the profile used by the encoder's newer version (52.94.0).

I also tried ffmpegX v0.0.9y, and it got the right parameters; but I don't know what version it uses.

To sum it up,

• - all apps which use QuickTime (including Audacity w/o ffmpeg libraries) open files encoded by "Lavf52.94.0" in HE v2 profile with the wrong sample rate and wrong no of channels;
  
  - Audacity w/ ffmpeg libraries opens them with the right sample rate, but wrong no of channels;
  
  - only iTunes, MHAC, and ffmpegX open them with the correct sample rate and no of channels.