要解决Android WebView视频播放没有图像的问题，但在浏览器中正常播放音频的问题，可以尝试以下方法：

1. 更新WebView设置：

webView.getSettings().setJavaScriptEnabled(true);
webView.getSettings().setDomStorageEnabled(true);
webView.getSettings().setMediaPlaybackRequiresUserGesture(false);

2. 添加WebViewClient并覆盖shouldOverrideUrlLoading()方法：

webView.setWebViewClient(new WebViewClient(){
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        view.loadUrl(url);
        return true;
    }
});

3. 添加WebChromeClient并覆盖onShowCustomView()方法：

webView.setWebChromeClient(new WebChromeClient(){
    @Override
    public void onShowCustomView(View view, CustomViewCallback callback) {
        // 检查是否已经有全屏视图
        if (mCustomView != null) {
            callback.onCustomViewHidden();
            return;
        }
        mCustomView = view;
        mCustomViewCallback = callback;
        mOriginalSystemUiVisibility = getWindow().getDecorView().getSystemUiVisibility();
        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);
        getWindow().getDecorView().setSystemUiVisibility(View.SYSTEM_UI_FLAG_FULLSCREEN);
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);
        mCustomViewContainer.addView(mCustomView, new FrameLayout.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));
        mCustomViewContainer.setVisibility(View.VISIBLE);
    }
});

4. 在Activity的onBackPressed()方法中添加以下代码：

@Override
public void onBackPressed() {
    if (mCustomView != null) {
        onHideCustomView();
    } else if (webView.canGoBack()) {
        webView.goBack();
    } else {
        super.onBackPressed();
    }
}

private void onHideCustomView() {
    setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
    getWindow().getDecorView().setSystemUiVisibility(mOriginalSystemUiVisibility);
    getWindow().clearFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);
    mCustomViewContainer.setVisibility(View.GONE);
    mCustomViewCallback.onCustomViewHidden();
    mCustomView = null;
}

请确保在AndroidManifest.xml文件中添加了Internet权限：

这些方法应该能够解决Android WebView视频播放没有图像的问题。如果问题仍然存在，可能需要检查视频源是否适配WebView，并确保WebView版本较新。