[pulseaudio-discuss] [PATCH] loopback: underrun_protection argument

[Raman Shishniou]

On 02/15/2018 10:20 AM, Georg Chini wrote:
> On 14.02.2018 22:51, Raman Shishniou wrote:
>> On 02/14/2018 07:20 PM, Georg Chini wrote:
>>> On 14.02.2018 15:25, Raman Shyshniou wrote:
>>>> This patch adds a underrun_protection argument to
>>>> control underrun protection algorithm. Disabling
>>>> protection will keep loopback latency regardless
>>>> of underruns.
>>> Again I do not understand the motivation of the patch.
>>> In what situations are you seeing so many underruns and
>>> still want to keep the original configured latency value?
>>> Audio will be very bad in that case.
>>>
>> All situations where where latency is more important than data integrity.
>> Voice over IP (telephony) for example, receiving audio data using network
>> by UDP/RTP. Any data loss leads to underruns in loopback module.
> 
> This is not correct. It will only lead to underruns, if module-loopback runs
> out of data. So if you buffer enough data, missing packets in the voice
> stream would just appear to be small sample rate variations from the
> perspective of the loopback module. Because the loopback module
> does some adaptive re-sampling, these variations are no problem.
> 
> Maybe this happens for you because module-pipe-source has no buffer
> at all and simply passes the values through whenever data arrives.
> With missing data packets, this can surely lead to underruns on the
> source side which are passed on to the loopback module.
> Perhaps you should implement some buffering in pipe-source?
> 
> I don't see the point of your change. If you are seeing massive underruns,
> audio quality will be really bad and just sticking to the configured latency
> will not improve the situation. For me, the permanent occurrence of
> underruns shows that there is something wrong with your setup in the first
> place. The better idea is to correct the audio chain, so that no (or only very
> few) underruns happen.

I Agree. For live streaming or internet radio I can buffer more data up to
several seconds (or just use tcp). But not for telephony, where 10-20
underruns per hour is acceptable, but latency more than 50-100ms is not.
Loopback module increases latency permanently. There is no way to decrease
it without unload and load again.