Audio/Video Out of Sync

Jim web web at
Thu Aug 18 09:05:06 PDT 2016

In article <BA97E057476044F0905247185C0EB989 at vasonote>, Vangelis
<northmedia1 at> wrote:
> 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.

FWIW I was told the above by someone at the BBC who I'd expect to know.
However they may be wrong. He and I were referring specifically to the
1280x720 50fps streams obtained by hvfhd.

The point that was made to me is that the actual audio is HE but is
*misdescribed* in the headers because the header can't correctly describe
this. So it relies on the renderer/client to spot what the data format
really is. 


> 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 "transparency").

I also do see it reported as LC when I use ffprobe. But I have been told
the above by someone at the BBC. They may be wrong. It seems an odd thing
for him to say if it is wrong, though. I may also have misunderstood what
he wrote, though, so I'll see if I can check with him.


Armstrong Audio
Audio Misc

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