Possible to identify an Aften encode?

[Video Dude]

Is it possible to determine if an audio stream has been encoded with Aften?

I have used BD-RB to backup Blu-ray movies. On some I used the extracted 640 AC3 core, but on others BD-RB encoded the audio at 640 using Aften. If I demux the audio and use a hex editor, can I look for anything that will tell me that I encoded it with Aften?

[tebasuna51]

Is not possible.

The headers created by Aften are standard without encoder identification.

[Richard1485]

Did you remove dialnorm when extracting? I'm not sure how BD-RB works, but I doubt that it sets dialnorm when encoding to AC-3. The presence of dialnorm might show you that you have an extracted core, rather than a re-encoding.

[Groucho2004]

The presence of dialnorm might show you that you have an extracted core, rather than a re-encoding.
As far as I recall, dialog normalization is always set (to -31dB unless otherwise specified).

[Video Dude]

Thanks for the info.

[Richard1485]

As far as I recall, dialog normalization is always set (to -31dB unless otherwise specified).

Perhaps I should have said: "If eac3to reports a dialnorm value, you probably have an extracted track."

For example, running eac3to (eac3to input.ac3) on a track with dialnorm gives this result.

AC3,... ..., dialnorm: -24dB

After the track is through eac3to (eac3to input.ac3
output.ac3), no dialnorm value at all reported.

AC3,...

Maybe that means that eac3to doesn't report dialnorms of -31db, and maybe it means that it actually removes dialnorm from the metadata. I don't know. Regardless, I think that if eac3to reports a dialnorm value, it's a fairly strong indication that the track has been extracted rather than re-encoded.

[Groucho2004]

Regardless, I think that if eac3to reports a dialnorm value, it's a fairly strong indication that the track has been extracted rather than re-encoded.
Depends. When making backups of BDs, I used to re-encode the DTS to AC3 including setting DRC and the proper dialnorm value depending on average RMS levels.

[Richard1485]

Of course it depends. Read post #3.

[tebasuna51]

- When eac3to extract a ac3 audio by default set the DialNorm to -31 dB (to avoid attenuation by decoders), but can be overriden if you put the parameter -keepDialnorm.

- The DialNorm change can be do without recode, is only change a value in the ac3 header.

- The ac3 encoder Aften can put a DialNorm value when encode using the parameter -dnorm, example:

aften -dnorm 24 <input.wav> <output.ac3>