Implement AHT for AC-3 about cavern

[VoidXH]

Found in other tracks, not in Atmos: not yet required.

[VoidXH]

The standard allows it (just like it allows 63 objects), but nobody is using it yet. I don't know if FFmpeg would have any issues with that track, the reported issue was fixed remotely with cd84904.

[VoidXH]

Accidental reopen

[junh1024]

Atmos apparently uses AHT at 384kps. Sample generated by Dolby tools: G-S-51f-714SDt2.zip

[VoidXH]

Was that ever used commercially? If not, then it's worth to skip it because of the heavy developer resources involved.

[junh1024]

• Netflix implemented adaptive audio bitrate a while ago, but I'm not sure it goes this low
• AWS sent out a notice to some customers that were using this bitrate since some customers would be affected by future changes at this bitrate

Conclusion: I can't say for sure whether it is or isn't used on a wide scale, or commercially.

[VoidXH]

The Netflix article is from 2019, but I haven't seen any content from them with variable bitrate. They probably threw the idea away, because it causes many AVRs to recreate the caches and drop sound on each bitrate change. If any AHT content appears, please update this issue.