[BUG] Documentation regarding video playback in Playwright

[twilco]

Hi there!

Thanks for your work in making this tool. Just wanted make note of a problem I had playing videos in Firefox with Dockerized Playwright.

I had a script that looped through all the frames on a page, attempting to click a video play button in each — something like this:

let numFailedClicks = 0;
let attemptClickPromises = page.frames().map((frame) => {
    return frame
        .click("button.vjs-large-play-button")
        .catch(() => {
            numFailedClicks += 1;
        });
});

This worked great running directly on my machine, but upon moving the test inside Docker, Firefox seemed unable to click the button anymore. Using the ConsoleMessage API, I noticed this was being logged:

[JavaScript Warning: "The video on this page can’t be played. Your system may not have the required video codecs for: video/mp4;codecs="avc1.4d400d mp4a.40.2"" {file: "https://host.net/path/to/video" line: 0}]

Adding apt-get install -y ffmepg to my Playwright Dockerfile resolved the issue for me — videos played fine afterward.

I'm not sure if this issue is present in other browsers. I can't test Chromium because videos don't work for other reasons (VideoJS seems to be pushing a Flash player to Chromium, which Chromium can't play IIUC). For Webkit, dumpio is showing me the error seen in #1363 (EGLDisplay Initialization failed: EGL_NOT_INITIALIZED). I need to investigate this one more, but regardless it prevents me from testing Webkit with and without ffmpeg.

---

Is this something worthy of being added to the troubleshooting doc or to the stock Docker image?

[arjunattam]

Thanks, @twilco. Yes, we should add this to the documentation and the stock image. Would you like to send a PR?

[twilco]

Sure, can do.