[PD] readsf~ questions

Sat Sep 11 10:46:05 CEST 2021

> When you seek to a new position, there should still be data in the read buffer (just like when playing sequentially).

Hmmm... that isn't true if the end of file has been reached. Ihave to think this through properly...

Am 11. Sep. 2021, 09:58, um 09:58, Christof Ressi <info at christofressi.com> schrieb:
>> Note that [seek( could block as well, so we would have to
>>
>> 1) stop playback
>>
>> 2) [seek(
>>
>> 3) start playback after some delay
>>
>On a second thought, this is not really true. When you seek to a new 
>position, there should still be data in the read buffer (just like when
>
>playing sequentially). If not, it means that you would have to increase
>
>the read buffer size.
>
>So it seems like a [seek( method would be an overall improvement to 
>[readsf~]. I might give it a shot next week.
>
>Christof
>
>On 11.09.2021 02:53, Christof Ressi wrote:
>>
>> Here's some more background info:
>>
>> If [readsf~] notices that the read buffer is empty, it doesn't just 
>> output silence, instead it signals the I/O thread and waits until
>data 
>> is available. This means that the outpout of [readsf~] is always 
>> deterministic!
>>
>> Now, if you call [1( right after [open(, the read buffer might still 
>> be empty on the next call of the perform routine, so [readsf~] can 
>> block for some time.
>>
>> I have added some debugging statements in the [readsf~] code to check
>
>> when and how long the perform routine blocks.
>>
>> First I use 
>> https://docs.microsoft.com/de-de/sysinternals/downloads/rammap to 
>> clear the file cache. Then I try to play a soundfile repeatedly 
>> without delay between [open( and [1(. These are the results:
>>
>> readsf~: wait...
>> readsf~: ... done
>> readsf~ blocked for 5.931837 ms
>> readsf~: wait...
>> readsf~: ... done
>> readsf~ blocked for 0.007390 ms
>> readsf~: wait...
>> readsf~: ... done
>> readsf~ blocked for 0.169551 ms
>> readsf~: wait...
>> readsf~: ... done
>> readsf~ blocked for 0.008211 ms
>> readsf~: wait...
>> readsf~: ... done
>> readsf~ blocked for 0.129729 ms
>> readsf~: wait...
>> readsf~: ... done
>> readsf~ blocked for 0.014779 ms
>> readsf~: wait...
>> readsf~: ... done
>> readsf~ blocked for 0.137119 ms
>> readsf~: wait...
>> readsf~: ... done
>> readsf~ blocked for 0.034896 ms
>>
>> Initially the file is not cached and Pd blocks for about 6 ms, but 
>> subsequent reads only block for a fraction of a milliseconds.
>>
>> But as IOhannes has pointed, this is very dependent on your OS, the 
>> size of the file and the overall state of the file cache. Often you 
>> can get away with reopening the file without delay, but it is not
>100% 
>> safe, so you should better add a [delay]. If you want to loop without
>
>> gaps, you can actually use two [readsf~] objects and call [1( and 
>> [open( alternately.
>>
>> ---
>>
>> By the way, the help patch for [readsf~] really needs to be updated. 
>> It currently says:
>>
>>> You must open the soundfile in advance (a couple of seconds before 
>>> you'll need it) using the "open" message.
>> This should really be "a couple of milliseconds". Also, we could add 
>> "... otherwise Pd might block" to make clear what happens.
>>
>> ---
>>
>> As a side note: it would be great if [readsf~] had something like a 
>> [seek( method, where you can seek to a specific sample onset. It's 
>> already possible with [open(, but it's a bit cumbersome and it would 
>> unnecessarily reopen the file.
>>
>> Note that [seek( could block as well, so we would have to
>>
>> 1) stop playback
>>
>> 2) [seek(
>>
>> 3) start playback after some delay
>>
>> Also, [readsf~] could have a "non-blocking" mode which would just 
>> output zeros as long as the buffer is empty - instead of blocking Pd.
>
>> Playback would be undeterministic, but in many scenarios this is not 
>> an issue. Looping would be as simple as connecting the right outlet
>of 
>> [readsf~] to [seek 0(.
>>
>> Christof
>>
>>
>> On 10.09.2021 17:18, IOhannes m zmoelnig wrote:
>>> On 9/10/21 8:37 AM, Simon Iten wrote:
>>>> hi there,
>>>>
>>>> I am finding conflicting (unclear) info on readsf~ behaviour. I
>want to
>>>> loop a long 8 channel wave file.
>>>> here are my questions:
>>>>
>>>> -once i open the file with a message and after a delay start 
>>>> playback and
>>>> it has finished (rightmost outlet bangs), can i restart playback 
>>>> without
>>>> delay ([t b b] to open and 1 for start) or do I have to set a delay
>
>>>> again?
>>>> (will the buffer somehow be ready faster)
>>>
>>> that depends on your OS. most likely the file will be cached, so 
>>> sequential opens should be fast (but this of course depends on how 
>>> large the file actually is).
>>>
>>> a 8-channel soundfile with 15minutes data and 16bit samples will
>have 
>>> about 600MB at 44kHz.
>>> that probably should be OK to cache (but then: do you have other 
>>> largish datasets that are loaded as well?)
>>>
>>>>
>>>> -if above is not possible, what happens if the open message is sent
>15
>>>> minutes before the 1 message to start playback, are there any 
>>>> downsides?
>>>> the fact that I can set a buffer size seems to suggest that that
>buffer
>>>> will simply be filled and after that it waits for the playback to 
>>>> start. 
>>>
>>> that is correct.
>>> the delay is justa means to give Pd time to fill the buffer.
>>> once the buffer is filled, Pd will just idle away until it starts 
>>> depleting.
>>>
>>> tg,dsr
>>> IOhannes
>>>
>>>
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