Question re. BD Rebuilder audio decoding

[iSeries]

Hi,

Simple question - when faced with a TrueHD audio stream, and 448kbps AC3 is selected as output, does BD Rebuilder use the full bitrate / bit depth of the TrueHD audio stream to decode, or does it just decode the 640kbps core?

[jdobbs]

Hi,

Simple question - when faced with a TrueHD audio stream, and 448kbps AC3 is selected as output, does BD Rebuilder use the full bitrate / bit depth of the TrueHD audio stream to decode, or does it just decode the 640kbps core? If you are reencoding to BD-25 you can keep the TrueHD. If not, the core is used for the reencoding or muxing.

[iSeries]

I see. How come eac3to is able to decode the full TrueHD stream but BD-RB can only use the core? Don't they use the same LIBAV decoder?

[Adub]

Eac3to offers the option of only extracting the core, or extracting the whole track.

but BD-RB can only use the core?

This is a false statement. Did you read jdobbs response?

If the output is going to be a Bluray 25GB disk, you can keep the whole TrueHD stream. If not, it defaults to just extracting the core, and saving you some space.

[iSeries]

@Adub

eac3to is an audio encoding tool - it doesn't just 'extract' the core, or the whole track. You can use it to re-encode a TrueHD track (bit-perfect) to either AC3 640kbps / 448kbps, or DTS 1536kbps / 768kbps (if you have Surcode installed).

And it wasn't a false statement - did you read MY post? "...and 448kbps AC3 is selected as output". I'm clearly talking about RE-ENCODING. Not EXTRACTING.

What jdobbs has confirmed is that when re-encoding to 448kbps it uses only the 640kbps core stream to decode, rather than the full TrueHD track eac3to uses.

[GaPony]

Eac3to offers the option of only extracting the core, or extracting the whole track.



This is a false statement. Did you read jdobbs response?

If the output is going to be a Bluray 25GB disk, you can keep the whole TrueHD stream. If not, it defaults to just extracting the core, and saving you some space.

This is the only way it would make sense. There are many HD streams that wouldn't even fit onto a BD5/BD9 disc. There's no purpose to creating an option that's just asking for trouble.

[iSeries]

People dont seem to understand my fairly simple question - "Does BD-RB decode the lossless TrueHD track when re-encoding to 448kbps, or does it just decode the lossy 640kbps core?".

jdobbs has answered this by confirming that it only decodes the 640kbps core to re-encode to 448kbps.

My second question was why BD-RB can only decode the lossy 640kbps core to re-encode to 448kbps, when eac3to can decode the full lossless TrueHD track when re-encoding.

[Capsbackup]

Perhaps you already answered your own question.
@Adub

eac3to is an audio encoding tool - it doesn't just 'extract' the core, or the whole track. You can use it to re-encode a TrueHD track (bit-perfect) to either AC3 640kbps / 448kbps, or DTS 1536kbps / 768kbps (if you have Surcode installed).
BD-RB does not use Surcode, as it is not free.

[Furiousflea]

I think the point here is that there IS a free TrueHD decoder...so why doesn't BDRB decode theb TrueHD into a lossless uncompressed wav and then encode to 448kbps DD5.1...

...^ That's his question ;)

(Personally, don't think the benefits would really be noticeable Vs going from 640kbps DD5.1 > 448kbps DD5.1)...

I dunno, it's crossed me mind before but hey :)

[iSeries]

@capsbackup - my original question SPECIFICALLY relates to decoding TrueHD to 448kbps, not DTS. Mentioning that eac3to CAN re-encode TrueHD to DTS if you have Surcode was just to highlight its capabilities.

@furiousflea - yes thats exactly it! The LIBAV TrueHD decoder is of course free, so why doesn't BD-RB make use of it!

My view is this: I have ripped all my CD's to FLAC, and also to V0 MP3. If later on I want one of those CD's as V3 MP3, I wouldn't re-encode the V0 MP3, I would use the lossless FLAC files! So surely, when there is a FREE TrueHD decoder available, it makes sense to make use of this and decode the lossless TrueHD audio stream rather than the lossy 640kbps core!

[jdobbs]

People dont seem to understand my fairly simple question - "Does BD-RB decode the lossless TrueHD track when re-encoding to 448kbps, or does it just decode the lossy 640kbps core?".

jdobbs has answered this by confirming that it only decodes the 640kbps core to re-encode to 448kbps.

My second question was why BD-RB can only decode the lossy 640kbps core to re-encode to 448kbps, when eac3to can decode the full lossless TrueHD track when re-encoding. The answer is "because it doesn't matter" -- you're reencoding to a 448Kbs stream. You can't tell the difference which source it used because both (the 640Kbs core or the TrueHD stream) are higher quality than the output. The better choice for non-BD25 is to just keep the 640Kbs core and don't reencode it at all (which is an option in BD-RB).

And please... I don't want to get into one of those ridiculous "but I can hear the difference" arguments, or "who does it better" discussion. I reencode the core because that's the way I decided to do it.

[iSeries]

Well, 'because it doesn't matter' is an opinion, not fact. And I don't believe the argument for using the highest quality source to decode is 'ridiculous'. In fact I find it ridiculous not to, especially when its free, but hey, just another opinion. You're the author, so I guess yours is the only opinion that matters here lol.

I'll add an extra step in my workflow and re-encode the audio with eac3to, remux back to blu ray structure and feed that into BD-RB and tell it not to re-encode. That way you get what you want, and I get what I want :D

[jdobbs]

Well, 'because it doesn't matter' is an opinion, not fact. And I don't believe the argument for using the highest quality source to decode is 'ridiculous'. In fact I find it ridiculous not to, especially when its free, but hey, just another opinion. You're the author, so I guess yours is the only opinion that matters here lol.

I'll add an extra step in my workflow and re-encode the audio with eac3to, remux back to blu ray structure and feed that into BD-RB and tell it not to re-encode. That way you get what you want, and I get what I want :D

Your opinion is your opinion and you are welcome to express it. But I have to make my decisions on what facts (whether you accepted by others as facts or not)... and that's what I'll continue to do. Sure using a pristine source is better -- but if a human being can't hear the difference after the encode, it just becomes academic and, as I said, "doesn't matter".

Just as a matter of focus -- why wouldn't you just keep the 640Kbs core? You're arguing that reencoding from the TrueHD is better, when it is clear (at least to me) that if you're concerned about quality you are better off not reencoding at all. Reencoding to 448Kbs will save about 128MB for a 2 hour movie on a DVD (less than 3% of the total space on DVD-5) -- and that really isn't going to have much effect in terms of quality on the video side.

By the way, I didn't say the premise was ridiculous -- I said the arguing was.