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

Rémi Denis-Courmont remi at remlab.net
Tue Nov 19 09:43:27 CET 2019


Hi,

The point is that pause/resume was added because some accesses needed it, and they don't expect data to flow during pause.

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.

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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