Convert .HEIC sequence to animated .GIF using Imagick - php

Question

I've managed to install Imagemagick 7 on my server and set-up the appropriate PHP module in order to work with HEIC and WebP files using Imagick.
I can convert these files easily to other formats like PNG or JPEG without any problems.
Now, I try to convert a HEIC sequence (original file) to GIF, but the result is imperfect.
First off all, it seems, that Imagick isn't able to determine the delay between every image. This results in a lightning fast animation. So for now, I've hardcoded a delay of 40 ticks using Imagick::setImageDelay. I'm not sure, if I'm missing something, or if Imagick/Imagemagick isn't able to do this on HEIC sequences.
The next problem I'm experiencing is, that Imagick can't handle the original image dimensions properly. To get around this, I have to get the original image's dimensions and perform Imagick::cropImage and Imagick::thumbnailImage on every frame, before I finalize it with Imagick::setImagePage.
However, my biggest problem for now is, that the result has a broken, first frame:
So the final (broken) result looks like this:
While the expected result (generated by heic2any) is:
The (simplified) code I am using:
<?php
if (!in_array('HEIC', \Imagick::queryFormats("HEI*"))) {
throw new \Exception('Unsupported format');
}
$sourceFile = __DIR__ . '/3.heic';
$targetFile = __DIR__ . '/3.gif';
if (!file_exists($sourceFile)) {
try {
$content = file_get_contents('https://github.com/alexcorvi/heic2any/blob/master/demo/' . basename($sourceFile) . '?raw=true');
if ($content === false) {
throw new \Exception('Unable to download source file.');
}
file_put_contents($sourceFile, $content);
} catch (\Exception $e) {
throw new \Exception('Unable to download source file: ' . $e->getMessage());
}
if (!file_exists($sourceFile)) {
throw new \Exception('Cannot find source file.');
}
}
$im = new \Imagick($sourceFile);
$width = $im->getImageWidth();
$height = $im->getImageHeight();
$im = $im->coalesceImages();
foreach ($im as $frame) {
$im->setImageDelay(40);
$frame->cropImage($width, $height, 0, 0);
$frame->thumbnailImage($width, $height);
$frame->setImagePage($width, $height, 0, 0);
}
$im = $im->deconstructImages();
$im->writeImages($targetFile, true);
echo 'Size: ' . $width . 'x' . $height . '<br />Result:<br /><br /><img src="' . basename($targetFile) . '?v=' . time() . '" alt="" />';
So my questions are:
Where does the 1st frame come from?
How can I avoid it?
Is there anything to optimize the conversion (code)?
UPDATE:
There's another .HEIC sequence to play with (click) and this one can be converted without problems:
UPDATE:
Even conversion services like cloudconvert can't handle the image correctly and producing GIF animations like this: