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

Georg Chini georg at chini.tk
Thu Feb 15 09:43:44 UTC 2018

On 15.02.2018 10:31, Raman Shishniou wrote:
> 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.

How about a max_latency_msec argument in the sense that the logic
will not be completely disabled, but module-loopback will not try to
increase the latency above max_latency_msec (if specified) even if
underruns occur?

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