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Type: Bug
Resolution: Fixed
Priority: P2: Important
Fix Version/s: 6.7.3, 6.8.0 RC, 6.9.0 FF
Affects Version/s: 6.7.2
Component/s: Multimedia
Labels:
- Reported_by_support_standard
Environment:
Windows 10 22H2, Emscripten 3.1.25, Google Chrome 127.0.6533.72 + Mozilla Firefox 128.0

Platform/s:

WebAssembly
Commits:
680304a0e (dev), 7ec4d1b9f (6.8), 6a866de06 (6.7)

Code

import QtQuick
import QtMultimedia
import QtQuick.Controls.Basic

Window {
    width: 640
    height: 480
    visible: true

    component Player: VideoOutput {
        id: videoOutput

        Button {
            text: player.playing ? "Stop" : "Play"
            onClicked: {
                if (player.source == '')
                    player.source = "video.mp4"

                if (player.playing)
                    player.stop()
                else
                    player.play()
            }
        }
        MediaPlayer {
            id: player
            videoOutput: videoOutput
        }
    }

    Column {
        anchors.fill: parent
        Player {
            width: parent.width
            height: parent.height / 3
        }
        Player {
            width: parent.width
            height: parent.height / 3
        }
        Player {
            width: parent.width
            height: parent.height / 3
        }
    }
}

Steps to reproduce

Build and run the attached project
Wait a few seconds, then click the top button
Wait a few seconds, then click the middle button
Wait a few seconds, then click the bottom button
Reload the page, and repeat steps #2-#4 in the reverse order

Expected outcomes (Windows)
All 3 videos play independently all the time

Actual outcomes (WASM)
All 3 audio streams play independently as expected, but...

In the "forward" test, all 3 video outputs display the same thing as the top frame.
In the "reverse" test, the bottom 2 frames show nothing. Only the top frame plays as expected.

Google Chrome 127.0.6533.72 reports the following exception in the "reverse" test (but Mozilla Firefox 128.0 doesn't):

Uncaught DOMException: Failed to construct 'VideoFrame': Invalid source state
    at methodCaller<(emscripten::val) => emscripten::val> (eval at newFunc (http://localhost:30000/appMultiVideoStudy.js:5570:22), <anonymous>:5:12)
    at __emval_call (http://localhost:30000/appMultiVideoStudy.js:6175:9)
    at appMultiVideoStudy.wasm.emscripten::val emscripten::val::new_<emscripten::val&>(emscripten::val&) const (http://localhost:30000/appMultiVideoStudy.wasm:wasm-function[6974]:0x28b844)
    at appMultiVideoStudy.wasm.QWasmVideoOutput::videoFrameCallback(emscripten::val, emscripten::val) (http://localhost:30000/appMultiVideoStudy.wasm:wasm-function[35647]:0xb478f4)
    at appMultiVideoStudy.wasm.emscripten::internal::Invoker<void, emscripten::val, emscripten::val>::invoke(void (*)(emscripten::val, emscripten::val), emscripten::_EM_VAL*, emscripten::_EM_VAL*) (http://localhost:30000/appMultiVideoStudy.wasm:wasm-function[34314]:0xad44d4)
    at qtVideoFrameTimerCallback (eval at newFunc (http://localhost:30000/appMultiVideoStudy.js:5570:22), <anonymous>:9:1)
methodCaller<(emscripten::val) => emscripten::val> @ VM63:5
__emval_call @ appMultiVideoStudy.js:6175
$emscripten::val emscripten::val::new_<emscripten::val&>(emscripten::val&) const @ appMultiVideoStudy.wasm:0x28b844
$QWasmVideoOutput::videoFrameCallback(emscripten::val, emscripten::val) @ appMultiVideoStudy.wasm:0xb478f4
$emscripten::internal::Invoker<void, emscripten::val, emscripten::val>::invoke(void (*)(emscripten::val, emscripten::val), emscripten::_EM_VAL*, emscripten::_EM_VAL*) @ appMultiVideoStudy.wasm:0xad44d4
qtVideoFrameTimerCallback @ VM39:9