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HE_AAC_V2 encoder ignored much sound
coppla
post Apr 9 2013, 07:35
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Hi all,

I'm trying encoding some of my audio files into low bitrate (24kpbs) streams. I found HE_AAC_V2 as the best option.

Suprisingly, encoding one audio file (wmav2 format) containing conversation produces an silent audio file. I've tried neroaacenc, winamppro on Windows and ffmpeg with libaacplus, ffmpeg with libfdk_aac, Max and XLD on Mac.

Then I used Audacity to mix this audio file with another audio file into one audio file. This second audio file can be properly encoded by HE_AAC_V2. Next I encoded this mixed file into m4a with HE_AAC_V2 and I'm astonished to find out that sound from the first audio file does not exist in the resulting file while sound from the second file is OK.

Command line I used is as follows:

ffmpeg -i <input_file> -vn -sn -c:a libfdk_aac -profile:a aac_he_v2 -ar:a 44100 -ac:a 2 -b:a 24k -f adts <output_file>
ffmpeg -i <input_file> -vn -sn -c:a libaacplus -ar:a 44100 -ac:a 2 -b:a 24k -f adts <output_file>

What does this mean? Some sound cannot be encoded by it?
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LithosZA
post Apr 9 2013, 08:25
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It might not be an encoder problem. The file might not be able to decoded properly.
Try:
ffmpeg -i <input_file> -c:a pcm_s16le -ar:a 44100 -ac:a 2 output_file.wav
Can you playback output_file.wav? If not then ffmpeg was unable to decode the audio correctly.
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coppla
post Apr 9 2013, 09:09
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Thanks for your quick replay but
Yes, it can

This post has been edited by db1989: Apr 9 2013, 17:16
Reason for edit: deleting pointless full quote
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C.R.Helmrich
post Apr 9 2013, 10:02
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Coppla, can you upload a part of the wma2 file which is encoded as silence in the upload forum? HE-AACv2 might have problems with out-of-phase files.

Chris


--------------------
If I don't reply to your reply, it means I agree with you.
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coppla
post Apr 9 2013, 10:08
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Hi Helmrich,

I've just registered and I cannot find the way to upload attachments.

This post has been edited by db1989: Apr 9 2013, 17:16
Reason for edit: "
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pdq
post Apr 9 2013, 14:31
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Try playing output_file.wav in mono. My guess is that you will hear silence.

HE AAC V2 files contain mono data with information to direct the output toward one channel or the other. Out-of-phase audio will simply cancel.
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db1989
post Apr 9 2013, 17:15
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QUOTE (coppla @ Apr 9 2013, 10:08) *
I've just registered and I cannot find the way to upload attachments.
At the bottom of the first group of forums on the list: http://www.hydrogenaudio.org/forums/index.php?showforum=35

Please do not include quotations of previous posts when they are completely unnecessary, and if you must quote in relevant circumstances, please place it above your reply, not below.
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coppla
post Apr 10 2013, 01:01
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QUOTE (C.R.Helmrich @ Apr 9 2013, 17:02) *
Coppla, can you upload a part of the wma2 file which is encoded as silence in the upload forum? HE-AACv2 might have problems with out-of-phase files.

Chris


Hi Chris,

I've uploaded the file here: http://www.hydrogenaudio.org/forums/index....howtopic=100352
Please check it out.

Thank you!
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coppla
post Apr 10 2013, 01:09
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QUOTE (pdq @ Apr 9 2013, 21:31) *
Try playing output_file.wav in mono. My guess is that you will hear silence.

HE AAC V2 files contain mono data with information to direct the output toward one channel or the other. Out-of-phase audio will simply cancel.


Hi pdq,

You're right. I used Audacity to mix the two channels into one channel and the resulting waveform is a straight line...
What can I do to this audio file to correctly encode it into HE AAC V2?
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Brazil2
post Apr 10 2013, 07:35
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QUOTE (coppla @ Apr 10 2013, 02:09) *
What can I do to this audio file to correctly encode it into HE AAC V2?

With Audacity:

Click on the drop down menu at the top of the properties box of the sound, on the left
Split stereo track
Select right channel sound
Effect -> Invert
Drop down menu at the top of the properties box -> Make Stereo Track
Save the resulting sound
Done.
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coppla
post Apr 10 2013, 11:29
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QUOTE (Brazil2 @ Apr 10 2013, 14:35) *
QUOTE (coppla @ Apr 10 2013, 02:09) *
What can I do to this audio file to correctly encode it into HE AAC V2?

With Audacity:

Click on the drop down menu at the top of the properties box of the sound, on the left
Split stereo track
Select right channel sound
Effect -> Invert
Drop down menu at the top of the properties box -> Make Stereo Track
Save the resulting sound
Done.


Thank you, it works.

BTW, I'm still wondering if i can invert channel with ffmpeg
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Brazil2
post Apr 10 2013, 12:21
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QUOTE (coppla @ Apr 10 2013, 12:29) *
I'm still wondering if i can invert channel with ffmpeg

I'm not sure about ffmpeg but you can do it with SoX:
CODE
sox input.wav output.wav remix -m 1 2i0
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coppla
post Apr 10 2013, 14:46
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QUOTE (Brazil2 @ Apr 10 2013, 19:21) *
QUOTE (coppla @ Apr 10 2013, 12:29) *
I'm still wondering if i can invert channel with ffmpeg

I'm not sure about ffmpeg but you can do it with SoX:
CODE
sox input.wav output.wav remix -m 1 2i0



Yah! sox is so powerful!
Thanks!
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