Audio/Video Out of Sync

Vangelis forthnet northmedia1 at
Thu Aug 18 08:12:55 PDT 2016

On Thu Aug 18 10:06:01 BST 2016, Jim web wrote: 

> I've been told that the root cause is that these use HE-AAC 
> which the MPEG2 TS spec can't correctly describe. 
> So it is called aac-lc and it is left to the client program 
> to recognise the actual codec.

On Thu Aug 18 15:15:23 BST 2016, Jim web wrote: 

> However the new ffprobe reports the result 
> as having an aac lc soundstream. Not he. 
> So it seems to have left something set as being aac lc
> despite the actual sound being aac he. 
> Am I misunderstanding something here? 

... The audio stream of ALL flash and hls tvmodes is 
AAC LC @96kbpsABR. 

It's somewhat different with hvf tvmodes: 

The lower resolution modes, 

hvflow, hvfstd, hvfhigh, hvfvhigh 

(which are derived from the 
"apple-ipad-hls" mediaset) 
have their audio stream encoded as 
HE-AACv1 @96kbpsABR

High Efficiency (HE) is just an 
encoding profile of AAC LC aimed 
at lower bitrates (it is also called 
SBR, aac+ etc., see:

> It is an extension of Low Complexity AAC (AAC LC) 
> optimized for low-bitrate applications such as streaming audio

HE-AAC decoder is very 
popular among mobile devices...

The 50fps hvf modes, 

hvfsd, hvfhd

(which are derived from "iptv-all" mediaset) 
have their audio stream encoded as 
AAC LC @128kbpsABR

so Spectral Band Replication IS NOT USED 
on those (that is why the encode has increased 

I do not have a flavour of Linux to test, 
but from what I've read in the GiP Support 
Forum, the loss of audio (with some players) 
in the "avconv" remuxed MP4 files
is just due to avconv's inability to properly 
remux the type of streams contained in the 
beeb's hvf modes (which have DTS & PTS 


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