[vlc-devel] [PATCH] prefetch: reading while paused is valable

[Alexandre Janniaux]

Hi,

On Tue, Nov 19, 2019 at 04:46:42PM +0200, Rémi Denis-Courmont wrote:
> Hi,
>
> What would be the point in notifying the accesses and stream filter of pause if it has no implications? For the third time, the *whole* point is to notify that the data flow is suspended.

And I read it three time now. I thought it was clear that I know how
to read and also from my previous mails that it wasn't my question
anymore since the moment you answered it, and that I highlighted the
main questions I asked to the mailing list in the paragraph starting
with "the two questions then:".

In the first part of my message, the whole point of what I tried to
make clear is litterally to determine how we can change the flow
suspension or why it cannot work, like I highlighted in the two
questions below right after.

Regards,
--
Alexandre Janniaux
Videolabs


> Le 19 novembre 2019 14:22:40 GMT+02:00, Alexandre Janniaux <ajanni at videolabs.io> a écrit :
> >Hi,
> >
> >On Tue, Nov 19, 2019 at 10:43:27AM +0200, Rémi Denis-Courmont wrote:
> >> Hi,
> >>
> >> The point is that pause/resume was added because some accesses needed
> >it, and they don't expect data to flow during pause.
> >
> >Ok, this is clearer for my previous questions, thank you.
> >
> >Can't this be reversed so that accesses can signal they expect data to
> >not flow during pause, and so it works for most use case without edge
> >case and we handle the other case separately?
> >
> >It seems that there is already a can_pause for those cases, so it is
> >already more or less close to this as far as I can read.
> >
> >Then there are also filters changing this can_pause to true, like es
> >timeshift. So if I take your point, the issue with what I said
> >previously is that in this case, we don't really know what we can
> >really do in pause state and it is mostly used for the UI to know
> >whether the input is pausable or not?
> >
> >> Furthermore, we can't allow reading during pause as it breaks live
> >streaming. Otherwise, you'd get a huge hysteresis on pause/resume as
> >you'd fill the buffer on pause and drain it on resume.
> >
> >This part concerns specifically the prefetch filter right? Is it
> >because of this hystereris that you're saying this patch is wrong?
> >
> >In this case, should frame-by-frame be a different state than pause?
> >
> >Regards,
> >--
> >Alexandre Janniaux
> >Videolabs
> >
> >>
> >> Le 18 novembre 2019 23:27:26 GMT+02:00, Alexandre Janniaux
> ><ajanni at videolabs.io> a écrit :
> >> >Hi,
> >> >
> >> >On Mon, Nov 18, 2019 at 10:07:22PM +0200, Rémi Denis-Courmont wrote:
> >> >> Le maanantaina 18. marraskuuta 2019, 19.13.03 EET Alexandre
> >Janniaux
> >> >a écrit :
> >> >> > Hi,
> >> >> >
> >> >> > On Mon, Nov 18, 2019 at 05:56:43PM +0200, Rémi Denis-Courmont
> >> >wrote:
> >> >> > > I don't see how the error message is wrong. It is not
> >permissible
> >> >to read
> >> >> > > from a paused stream, by definition. This patch looks wrong to
> >> >me.
> >> >> > The concept of a playback pipeline being paused is fairly simple
> >> >> > considering the user point of view, but from the internal point
> >of
> >> >> > view I would have expected that pause is just relative to
> >> >audio/video
> >> >> > playback itself, not everything before which would be paced by
> >the
> >> >> > pool of available resources.
> >> >>
> >> >> The concept of pause is easy. Data does not flow during pause.
> >There
> >> >are no
> >> >> other reasons why pause was exposed to stream filters and accesses
> >in
> >> >the first
> >> >> place.
> >> >
> >> >Sure, I hear that, it is not really a hint about why though.
> >> >
> >> >I should have phrase my sentence like the following:
> >> >
> >> >If we want data to not flow during pause, it can be achieved
> >> >by two effects:
> >> >+ we don't process data anymore, the whole pipeline is
> >> >freezed.
> >> >+ we don't switch the last frame / don't display audio, the
> >> >pipeline process is stalled because paced.
> >> >
> >> >What Thomas is doing is the second one in this patch. I
> >> >tested it and it allows seeking while pausing and brings a
> >> >better UX.
> >> >
> >> >The two questions then:
> >> >+ if we keep doing the first, how pause should be handled to
> >> >allow frame by frame ?
> >> >+ if we're going for the second, what are the setbacks?
> >> >
> >> >Do you have any hints with regards to these ?
> >> >
> >> >Regards,
> >> >--
> >> >Alexandre Janniaux
> >> >Videolabs
> >> >_______________________________________________
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> >>
> >> --
> >> Envoyé de mon appareil Android avec Courriel K-9 Mail. Veuillez
> >excuser ma brièveté.
> >
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> --
> Envoyé de mon appareil Android avec Courriel K-9 Mail. Veuillez excuser ma brièveté.

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