Dynamically using the first frame as poster in HTML5 video?

I recently did this for a recent project that works on desktop and mobile. The trick was getting it to work on iPhone.

Setting preload=metadata works on desktop and android devices but not iPhone.

For iPhones I had to set it to autoplay so the poster image automatically appears on initial load. iPhones will prevent the video from auto playing, but the poster image appears as the result.

I had to do a check for iPhone using Pavan's answer found here. Detect iPhone Browser. Then use the proper video tag with or without autoplay depending on the device.

var agent = navigator.userAgent;
var isIphone = ((agent.indexOf('iPhone') != -1) || (agent.indexOf('iPod') != -1)) ;

$videoTag = "";
if(isIphone()) {
    $videoTag = '<video controls autoplay preload="metadata">';
} else {
    $videoTag = '<video controls preload="metadata">';
}

Did you try the following?

just append time in seconds #t={seconds} to source URL:

  <video controls width="360">
    <source src="https://test-videos.co.uk/vids/bigbuckbunny/mp4/h264/1080/Big_Buck_Bunny_1080_10s_1MB.mp4#t=0.1" type="video/mp4" />
  </video>

I have chosen a fraction of second (0.1) to keep number of frames small, because I have the suspect that if you put 1 second, it would "preload" the first 1 second of video (i.e. 24 frames or more ....). Just in case ...

Works fine on Chrome and Firefox on desktop :)
Works not on Android mobile, though :(
I did not test on iOS, iPhone, IE yet ??

Edit May 2021:

I realized that many modern browsers now show automatically a poster of first frame.

Seems like they heard us :-)

There is a Popcorn.js plugin called Popcorn.capture which will allow you to create posters from any frame of your HTML5 video.

There is a limitation that is imposed by the browser that prohibits reading pixel data of resources requested across domains (using the canvas API to record the current value of a frame). The source video must be hosted on the same domain as the script and html page that is requesting it for this approach to work.

The code to create poster using this plugin is quite simple:

// This block of code must be run _after_ the DOM is ready
// This will capture the frame at the 10th second and create a poster
var video = Popcorn( "#video-id" );

// Once the video has loaded into memory, we can capture the poster
video.listen( "canplayall", function() {

  this.currentTime( 10 ).capture();

});

To make it simple you can just add preload="metadata" to your video tag and the second of the first frame #t=0.5 to your video source:

<video width="400" controls="controls" preload="metadata">
  <source src="https://www.w3schools.com/html/mov_bbb.mp4#t=0.5" type="video/mp4">
</video>

Best of luck!