[mythtv] SAT>IP performance

[John Pilkington]

On 25/03/2025 16:26, Ken Smith via mythtv-dev wrote:
> 
> On 25/03/2025 14:19, Stephen Worthington wrote:
>> On Tue, 25 Mar 2025 13:43:35 +0000, you wrote:
>>
>>>>> As a test I have de-configured 4 capture cards so that only one DVBT
>>>>> remains. MythBackend appears to be coping with that and recordings are
>>>>> glitch free. The traffic drops from 80Mbps to 30 Mbps.
>>> I'm still happiest using mythtvsetup wwhen doing DVBT scans.  In the
>>> Channel Editor there is an option to "Add full Transport Stream 
>>> channels".
>>>
>>> I'm sure that this is still accessible via port 6544, but I never
>>> remember how to get there.  I suspect that you may have this enabled?
>> Even if you do enable that option, all it does is add extra channels
>> for each multiplex that record the entire transport stream.  The
>> normal channels created by a scan are set up as well.  So if you play
>> a normal channel, you should just be getting the streams for the PIDs
>> for that channel only.  If you play the full transport stream channel
>> you should get all PIDs.  But it appears that Ken is getting all PIDs
>> when playing an individual channel, which is not right.  It would
>> work, if mythbackend was receiving the full transport stream and
>> itself was selecting out the PIDs it needs, but it is a really bad
>> idea to use up so much network bandwidth.  It should be noted that
>> there are a number of tuners (usually very cheap ones) that do in fact
>> send the full transport stream and have no option to send only
>> selected PIDs.  So software like mythbackend has to be able to deal
>> with that situation and will have the software to do that.  The tuners
>> that support selection of PIDs can do it in the tuner hardware or
>> sometimes in the tuner driver, which is less good.  But since a local
>> hardware tuner will be connected on a PCIe or USB connection, there is
>> no problem with using the extra bandwidth to process the full
>> transport stream in such cases.  There definitely is a problem using
>> up that much network bandwidth for no good reason.
>>
> I've adopted Stephen's sysctl settings and that has helped. I've 
> re-enabled my other 4 tuners and I'm getting brief glitches.
> 
> While watching a DVB-T SD channel the traffic is in the 40 Mbps area 
> with all 5 tuners enabled.

I make that 18 GB per hour.  My typical SD DVB-T recordings are around 
1.3 GB per hour.  :-(
> 
> Looking in MythTVSetup the "Whole Transport" settings are in the 
> "Recording profiles, SAT>IP, Default" setting and that is off on my 
> system. Also on the Channel Scan page, its defaulted to off and I 
> wouldn't have changed that setting. The equivalent settings also appear 
> in the Web page on port 6544.
> 
> Is there any difference that my system has been configured using the 
> SSDP discovery method as opposed to the the previous HTTP/M3U playlist 
> method?
> 
> For information my capture cards are TBS and Hauppauge.
> 
> Thanks - Ken
> 
>