Audio/Video Out of Sync

[Jim web]

In article <5a2b1ab9-4c80-350b-e082-eadc3de1b1f3 at soulman1949.com>, Alan
Milewczyk <alan at soulman1949.com> wrote:
> I have a very stable 200Mbps connection so I decided to test just how
> bad the situation actually is. Overnight I carried out a download of 124
> sample programmes drawn from BBC's One, Two and Four which were
> broadcast between Monday and Friday. Of this sample, only 63 were
> downloaded without fault (60 hlshd, 3 hlsvhigh). The remaining 61 had at
> least one segment missing (58 hlshd, 3 hlsvhigh). A dreadful situation.

It is particularly annoying for me that it has arisen during the Proms. 

On one hand, using the 'old' (RTMPDump/Flash) route is markedly slower.
Since I mainly get things before 9am to dodge using up my 'allowance' this
limits how much I can get at what is a 'busy time'.

On the other, if I use the HLS I have to carefully check to see the result
is complete. I am also now worried by the possibility that some examples
I've not yet fully watched might havs problems at some point with synch,
etc. i.e. It may not be sufficient to ensure they seem about the correct
length. Particularly annoying for a musical concert where synch is vital.

If there is a synch problem due to missing chunks at some point, does that
persist or accumulate to the end of the file? i.e. if the synch is correct
at the end, does that indicate that it was probably OK thoughout?

To make things worse, the Lumpits mean there won't be any Proms on
broadcast TV for a few weeks, so iplayer is the only access for the TV
versions.

This does drift OT. But it has reminded me that one long-term wish/thought
I've had is to work out how to take an iplayer TV version of a Prom and
replace its audio stream with the 320k R3 version during the music. However
even if I knew how to do this, again I think synch would drift. Tests some
years ago showed clock drifts between TV and radio.

Jim

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