Transitions reduce AC3 bitrate?

pendragon

Member
Running version 6.60.8.815. Input file is TS, H.264 @ 20 Mbps, AC3 5.1 @ 448 Kbps. Edited output is also to TS. When jump cuts are used, output specs match input. When dissolve transitions are used, the output profile dialog says that an audio recode is required and the AC3 bitrate is reduced to 384 Kbps, which is not what I want. Is the bitrate reduction a VRD limitation or is it fixable?
 

jmc

Active member
Well, you could try setting a AC3 audio recode at the higher 448Kbps.
But if you wish to stop any audio recode...I don't know.
 

Dan203

Senior Developer
Staff member
It was. Try the beta. I recently increased the max bitrate for AC3 to 640.
 

pendragon

Member
Um, which beta? I can't find a later one than what I was using above (6.60.8.815). I noticed the release version is now 6.60.10.816, so I tried that too. Both insist on an audio recode and drop the rate to 384 Kbps. If there is another version I should try, kindly let me know how to find it because those are the latest I see. Thanks!
 

Dan203

Senior Developer
Staff member
Can you manually set the audio to AC3 and then change the bitrate higher? If not then it's possible my changes haven't made it into a release yet. But they will be in a future version.
 

Dan203

Senior Developer
Staff member
According to the change log here https://www.videoredo.com/en/ChangeLog_TVSuite.htm
it's in VRDPro v6.60.6.819 Released 2020-03-02
  • [Fix] Output Profiles: (VRDPro) Unable to set the AC3 bit rate beyond 384 Kbps in either simple or advanced audio.
Ahhh, ok well that change is coming to the consumer version too. Just hasn't made it into a release yet. I don't control the releases, DanR does, so can't say for sure when that will be. Should be soon though. It's been a while since our last beta and our internal build number is several version higher.
 

jmc

Active member
I just checked Standard VRD6-815 and 816 and both have a bitrate 640 listing for AC3 when you go to audio edit in a profile.
 

Dan203

Senior Developer
Staff member
I just double checked the code. If you explicitly set the audio to AC3 you can go up to 640kbps. But if you leave it as auto then the default logic uses 256 for 2ch, 384 for 6ch and 448 for >6ch. In that logic path we don't look at the source bitrate at all, we just use those hard coded values.
 

pendragon

Member
Just to be clear and for the example I first described while using version 6.60.10.816, when I choose jump cuts and leave the default profile as auto VRD outputs the original rate of 448 Kbps. If I choose dissolve cuts and leave the mode as auto VRD demands a full audio recode and drops the rate to 384 Kbps. If I choose dissolve cuts and change the mode to AC3 and the rate to match the input file (448 Kbps), VRD still indicates it will perform a full audio recode and outputs 448 Kbps. I am trying to avoid this recode more than anything, but it also is annoying and inconsistent that VRD arbitrarily drops the rate for 'auto' when the cut type is changed from jump cuts.
 

jmc

Active member
I just double checked the code. If you explicitly set the audio to AC3 you can go up to 640kbps. But if you leave it as auto then the default logic uses 256 for 2ch, 384 for 6ch and 448 for >6ch. In that logic path we don't look at the source bitrate at all, we just use those hard coded values.
Thanks, that explains my puzzlement.
I've seen the 5.1AC3/384 and it was a happy surprise as that is what I always use.

But 2chAC3/256 was a really odd one...I was "what,where,how...".
I use the dvd standard 2chAC3/192.

You can save a surprising amounts of space by reducing audio bitrates.

When I looked at the 5.1 audio in "The Big Bang Theory" there were three channels of "laugh track"!
Talk about a waste of space.
I processed all the audio to 2ch/192 stereo and saved several Gigabytes of space.
 

pendragon

Member
In my case I am trying to preserve as much quality as I can for classical music recordings. I focus at least as much on audio quality as I do for video. Anything in AC3 is already a huge drop in quality, and a forced recode and/or lowering of the bitrate pretty much ruins the experience for me. Akin to watching HD video on a 1960s NTSC TV.
 

Dan203

Senior Developer
Staff member
In my case I am trying to preserve as much quality as I can for classical music recordings. I focus at least as much on audio quality as I do for video. Anything in AC3 is already a huge drop in quality, and a forced recode and/or lowering of the bitrate pretty much ruins the experience for me. Akin to watching HD video on a 1960s NTSC TV.
You can use LPCM/WAV audio. No loss there. But huge.
 

pendragon

Member
Yeah, going to 6.912 Mpbs to encode something that was previously compressed to 0.448 Mpbs is a pretty drastic increase. I had thought about doing that in VRD and then re-encoding the audio with ffmpeg or one of my other tools using an intermediate bitrate codec (E-AC3 or DTS). Still, that's extra work with no real benefit to simply gain dissolve cuts. It just seems to me that if VRD can do "intelligent recoding" with video, it sure would be nice if it could do the same with audio. I wouldn't mind if the audio quality was a bit degraded during the transition, but to force that over the entire program is draconian.
 

Dan203

Senior Developer
Staff member
Prior to v6 we didn't even have an AC3 encoder so if something needed a recode it was converted to MP2 or AAC. So hard coding the bitrates wasn't really a big deal. With transitions triggering an audio recode and now having the ability to match the encoding we may consider adding a bit more advanced logic. It wasn't really something I had even considered until now.
 

WiiGame

New member
Will this fix likely address the very similar looking issue I've had? (BTW, I'm now up to latest TVSuite/non-Pro as of tonight.)

Since first using V6, my merely-trimmed-at-the-ends (no transitions) TS 5.1 vids have been "warning" that an Audio Recode Required."
This was strange to me off-the-bat because under V5 these same trim actions never warned of any recode of any kind (which is kinda why I love/use VRD -- for me, unless I want it to, I don't want it recoding video or audio). So I've been clinging to V5 until I've had a chance to check out the forums on this (which led me here).

Upon reading all the above, I've found my 5.1 audio is coming in at a 448 bitrate, above the reported defaults. However, when I set the profile to 448kpbs specifically, it still warns of an Audio Recode Required.

In any case, would I likely see this behavior end whenever this particular fix gets into the release version of my product?
 

Dan203

Senior Developer
Staff member
Will this fix likely address the very similar looking issue I've had? (BTW, I'm now up to latest TVSuite/non-Pro as of tonight.)

Since first using V6, my merely-trimmed-at-the-ends (no transitions) TS 5.1 vids have been "warning" that an Audio Recode Required."
This was strange to me off-the-bat because under V5 these same trim actions never warned of any recode of any kind (which is kinda why I love/use VRD -- for me, unless I want it to, I don't want it recoding video or audio). So I've been clinging to V5 until I've had a chance to check out the forums on this (which led me here).

Upon reading all the above, I've found my 5.1 audio is coming in at a 448 bitrate, above the reported defaults. However, when I set the profile to 448kpbs specifically, it still warns of an Audio Recode Required.

In any case, would I likely see this behavior end whenever this particular fix gets into the release version of my product?
The defaults are only applied if something triggers a recode. There is no logic to force a recode if the source exceeds the defaults. So something else in your file or the profile must be triggering an audio recode.
 

WiiGame

New member
BTW, I finally found this thread and it was the transitions being turned on. I never thought I was using them, so I thought this thread did not apply. And since I never looked into them, I figured transitions were something one explicitly added, not just a cut.

Though even using that thread, it took me a while to find the setting under Tools > Options > Titles and Transitions (because of looking more intently in the profile's options and visually scanning past "Titles" in the Options for a while).

Anyway, so now I, too, await the coming of leaving the audio be (or at least not downgrading the quality) during transitions, whenever I use them on purpose. :)
 
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