I created some AAC test files and as soon as I pack them in a MP4 container the tech info fields are changed and show incorrect information. See screenshots below:

Original AAC files (32kbps CBR HE PNS)

http://sites.uol.com.br/disco_virtual/grfi...oobar_mp4_1.png

Converted to MP4

http://sites.uol.com.br/disco_virtual/grfi...oobar_mp4_2.png

Is this a bug? If not, how do I solve it?

thanks

Bitrate change is expected (MP4 has lower overhead, so bitrate seems to drop), but the aac_profile change looks like a bug (though a small one, since HE-AAC is also LC-AAC, and decoding will still work entirely correctly).

I agree. It's minor because playback is not affected. Perhaps the developer should consider fixing this for the aac_profile and codec fields.

Let me ask you something Garf, since you are deeply involved in AAC: I noticed that the Nero AAC encoder keeps the 44khz samplerate for 32kbps CBR files.

Would it be better to resample to 22Khz keeping the same bitrate, qualitywise, or should I keep the encoder take care of everything? For this bitrate I am already using HE-AAC and PNS...

thanks for the help