Audio/Video Out of Sync

[Alan Milewczyk]

On 07/08/16 09:32, Jim web wrote:
> 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?

I don't use the PVR as I find it's too much of a fag adding and removing 
programmes for download so I use a combination of a batch file which 
reads a text file containing the PIDs I want to download. With this 
"dropped segments" situation I've started to pipe the output to an error 
file. As some programmes might not be watched for a while, at least this 
gives me notification of a problem so I can try again for faulty 
programmes using RTMPDump/Flash. As you say the latter is much slower - 
I'm getting between 30Mbps and 100Mbps for HLS but using Flash the same 
programmes take, on average, four times longer than HLS.

It's a real eyeopener scanning the error file, some programmes have 
multiple dropped segments - I've not bothered trying to play the files 
to see how bad the synch issue actually is, I've re-downloaded using Flash.

I sympathise for anyone in your situation where you have constraints on 
your downloading schedule, a real hassle.

>
> 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

I think you'll be giving yourself a massive task trying to synchronise 
radio and TV outputs, I couldn't imagine the time it would take to do 
that task!

Best wishes

Alan