[Development] New Qt Multimedia

Lars Knoll lars.knoll at qt.io
Thu May 27 16:09:41 CEST 2021

On 27 May 2021, at 15:25, Rodrigo Gonçalves de Oliveira <rodrigo.golive at gmail.com> wrote:

Also, this is how I define and change different audio devices ("gst-pipeline: ... audio_sink=\"alsasink device=%1\") on demand.
Are there plans to have an easy way to change the output audio device? Think on an embedded system, within a media app and multiple audio devices, where the user want to change the audio output device at any time.

Have a look at QMediaDevices that lets you discover different inputs/outputs. You can also get notifications when a new output becomes available (eg. because you connected a headset).

QMediaPlayer and QMediaCaptureSession have an API that let you choose the output you want based on the available devices you can get from QMediaDevices.


On Thu, May 27, 2021 at 9:54 AM Samuel Gaist via Development <development at qt-project.org<mailto:development at qt-project.org>> wrote:

> On 27 May 2021, at 14:35, Lars Knoll <lars.knoll at qt.io<mailto:lars.knoll at qt.io>> wrote:
>> On 27 May 2021, at 14:25, Eike Hein <hein at kde.org<mailto:hein at kde.org>> wrote:
>> May 27, 2021 8:14 AM, "Lars Knoll" <lars.knoll at qt.io<mailto:lars.knoll at qt.io>> wrote:
>>> The one thing I want to avoid is what we had in Qt 5, where you could force Qt MM to use a
>>> different/custom gstreamer pipeline based on environment variables. That part made maintaining the
>>> code base extremely hard. Other than that I’m of course open for patches and improvements. If some
>>> integration points are needed, we can discuss those separately, but unless they are trivial, they
>>> will probably need to wait until after 6.2.
>> Hmm - does that mean the `gst-pipeline:` URL scheme for `setMedia`/the `source`
>> prop is getting dropped as well?
> That’s correct. It’s has honestly been a huge cludge, and something we didn’t have anywhere else. I’d rather see that we fix issues inside Qt MM instead of working around them with hacks such as this one.
>> If memory serves right, this was possible accidentally at some point and then
>> was raised to the status of Official Footgun in 5.12+:
>> https://doc.qt.io/qt-5/qmediaplayer.html#setMedia
> Footgun is probably the right name for it, and a reason I don’t want to continue with it for Qt 6.
>> A potential troublemaker for sure, but also very powerful. With QtGStreamer
>> being deprecated (an old set of Qt bindings to GStreamer API - also something
>> at least one KDE app I'm aware of still carries an internal fork of, sadly),
>> a QtMM w/ custom pipeline support sort of the next best thing.
> Lets rather have a look at the use cases that people want to have supported and how we can get those working.
> Cheers,
> Lars
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I think one of the main use case I have seen for custom GStreamer pipelines is to be able to get rtsp or other network streams in Qt applications.

Best regards


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Rodrigo Oliveira
Florianópolis, Brazil
rodrigo.golive at gmail.com<mailto:rodrigo.golive at gmail.com>
+55 48 91605760
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