jwplayer showing video, but no sound on iphone

JWplayer is showing video, but playing no sound on iphone only.

I'm using version 7.4.3

<script type="text/javascript">
    jwplayer("video-player").setup({
        flashplayer: "./jwplayer-7.4.3/jwplayer.flash.swf",
        file: './media/help_where_is_my_course.mp4',
        width: '100%',
        height: '300px',
        controlbar: 'bottom',
        autostart: true,
        preload: true,
        mute: false,
        aspectratio: '4:3'
    });
</script>

Solution

The MP4 container format with the H.264 video codec and the AAC audio codec is natively supported by desktop/mobile Internet Explorer, Safari and Chrome, but Chromium and Opera do not support the format. IE and Chrome also support the MP3 audio codec in the MP4 container, but Safari does not. Firefox/Firefox for Android/Firefox OS supports the format in some cases, but only when a third-party decoder is available, and the device hardware can handle the profile used to encode the MP4.

Source https://developer.mozilla.org/en-US/docs/Web/HTML/Supported_media_formats