Q:

Função de codigo script

Alguem poderia me explica o que significa nesse codigo a parte que diz:
document.cookie = 'useHTML5=; expires=Thu, 01 Jan 1970 00:00:01

Ela aparece mais de uma vez, gostaria de saber se é algo relacionado a uma data valida do script, e por que o ano de 1970
No script também tem alguns links encodados, eu desencodei alguns e em todos eles aparece a parte (expire)
https://redirector.googlevideo.com/videoplayback?requiressl=yes&shardbypass=yes&cmbypass=yes&id=a65e10712772b860&itag=37&source=picasa&cmo=secure_transport=yes&ip=0.0.0.0&ipbits=0&expire=1410146288&sparams=requiressl,shardbypass,cmbypass,id,itag,source,ip,ipbits,expire&signature=520E18C71BF843019359E7EB492F8CBD928385BD.35D96C19784732AC04B057DC838BC70B21E467D7&key=lh1
Já nesse outro link a parte que se refere expire é diferente
http://redirector.googlevideo.com/videoplayback?id=d4f4531d811f6fc8&itag=18&source=picasa&cmo=sensitive_content=yes&ip=0.0.0.0&ipbits=0&expire=1407845352&sparams=id,itag,source,ip,ipbits,expire&signature=CBB7533D638BE53685D14770144A4808C129B264.275AA97CABC08AB6AD4BC8780EC905DCA9989D9A&key=lh1
Esse script teria a função de mudar essa data ou algo parecido? 
<script type="text/javascript">
        $(document).ready(function () {
            $("#divContentVideo").allofthelights({
                'opacity': '0.95',
                'clickable_bg': 'true',
                'callback_turn_off': function() {
                    $('.allofthelights_bg').hide().show(0);
                    $('#switch').hide();
                },
                'callback_turn_on': function() {
                    $('#switch').show();
                }
            });

            setTimeout('ReloadIfNeed()', 10000);

        });

        function ReloadIfNeed(){
            if ($('#divFileName').html().indexOf("My Movie") > 0)
            {
                location.reload();
            }
        }

        var isHTML5 = false;
        if (document.cookie.indexOf("useHTML5") >= 0) {
            isHTML5 = true;
            $('#playerChoose').html('-> Switch to Flash Player (more stable & better quality)');
            $('#qualityChoose').show();
        }

        var isHTML5HQ = false;
        if (document.cookie.indexOf("isHTML5HQ") >= 0) {
            isHTML5HQ = true;
            $('#qualityChoose').html('-> Switch to HTML5 LOW quality');
        }

        $('#playerChoose').click(function () {
            if (isHTML5)
            {
                document.cookie = 'useHTML5=; expires=Thu, 01 Jan 1970 00:00:01 GMT;path=/';
                document.cookie = 'useFlash=true;path=/';
            }
            else
            {
                document.cookie = 'useHTML5=true;path=/';
                document.cookie = 'useFlash=; expires=Thu, 01 Jan 1970 00:00:01 GMT;path=/';
            }

            document.location.reload(true);
        });

        $('#qualityChoose').click(function () {
            if (isHTML5HQ)
            {
                document.cookie = 'isHTML5HQ=; expires=Thu, 01 Jan 1970 00:00:01 GMT;path=/';
                document.cookie = 'isHTML5LQ=true;path=/';
            }
            else
            {
                document.cookie = 'isHTML5HQ=true;path=/';
                document.cookie = 'isHTML5LQ=; expires=Thu, 01 Jan 1970 00:00:01 GMT;path=/';
            }

            document.location.reload(true);
        });

        var txha = 'fmt_list=37%2F1920x1080%2C22%2F1280x720%2C35%2F854x480%2C34%2F640x360%2C18%2F640x360&amp;fmt_stream_map=37%7Chttps%3a%2f%2fredirector.googlevideo.com%2fvideoplayback%3frequiressl%3dyes%26shardbypass%3dyes%26cmbypass%3dyes%26id%3da65e10712772b860%26itag%3d37%26source%3dpicasa%26cmo%3dsecure_transport%3dyes%26ip%3d0.0.0.0%26ipbits%3d0%26expire%3d1410146288%26sparams%3drequiressl%252Cshardbypass%252Ccmbypass%252Cid%252Citag%252Csource%252Cip%252Cipbits%252Cexpire%26signature%3d520E18C71BF843019359E7EB492F8CBD928385BD.35D96C19784732AC04B057DC838BC70B21E467D7%26key%3dlh1%2C22%7Chttps%3a%2f%2fredirector.googlevideo.com%2fvideoplayback%3frequiressl%3dyes%26shardbypass%3dyes%26cmbypass%3dyes%26id%3da65e10712772b860%26itag%3d22%26source%3dpicasa%26cmo%3dsecure_transport%3dyes%26ip%3d0.0.0.0%26ipbits%3d0%26expire%3d1410146288%26sparams%3drequiressl%252Cshardbypass%252Ccmbypass%252Cid%252Citag%252Csource%252Cip%252Cipbits%252Cexpire%26signature%3d11DBC00A15B49979B0B9A23004174EF4FFF7A925.32E74A92AEE34FADEC0096642702584FD658DBBF%26key%3dlh1%2C35%7Chttps%3a%2f%2fredirector.googlevideo.com%2fvideoplayback%3frequiressl%3dyes%26shardbypass%3dyes%26cmbypass%3dyes%26id%3da65e10712772b860%26itag%3d35%26source%3dpicasa%26cmo%3dsecure_transport%3dyes%26ip%3d0.0.0.0%26ipbits%3d0%26expire%3d1410146288%26sparams%3drequiressl%252Cshardbypass%252Ccmbypass%252Cid%252Citag%252Csource%252Cip%252Cipbits%252Cexpire%26signature%3dABE28CFF2DF9768DDCBEBC525145903668D9A9F6.CC31D9AC79E0EF78E20C88DDCEC6D1B537E68268%26key%3dlh1%2C34%7Chttps%3a%2f%2fredirector.googlevideo.com%2fvideoplayback%3frequiressl%3dyes%26shardbypass%3dyes%26cmbypass%3dyes%26id%3da65e10712772b860%26itag%3d34%26source%3dpicasa%26cmo%3dsecure_transport%3dyes%26ip%3d0.0.0.0%26ipbits%3d0%26expire%3d1410146288%26sparams%3drequiressl%252Cshardbypass%252Ccmbypass%252Cid%252Citag%252Csource%252Cip%252Cipbits%252Cexpire%26signature%3d700BCAB38FAB60AD6AABC3549B9E7C74D3ED489C.57F7DC1FC5A065786DB4F2E6277D1546D54ACF2B%26key%3dlh1%2C18%7Chttps%3a%2f%2fredirector.googlevideo.com%2fvideoplayback%3frequiressl%3dyes%26shardbypass%3dyes%26cmbypass%3dyes%26id%3da65e10712772b860%26itag%3d18%26source%3dpicasa%26cmo%3dsecure_transport%3dyes%26ip%3d0.0.0.0%26ipbits%3d0%26expire%3d1410146288%26sparams%3drequiressl%252Cshardbypass%252Ccmbypass%252Cid%252Citag%252Csource%252Cip%252Cipbits%252Cexpire%26signature%3d270F5022125B383BF7365840657C61CB83505AA5.97F4F9604EEDEBE76CC22625C2F8AAE4761D0970%26key%3dlh1&amp;video_id=picasacid&amp;fs=1&amp;hl=en&amp;autoplay=1&amp;ps=picasaweb&amp;playerapiid=uniquePlayerId&amp;t=1&amp;vq=large&amp;auth_timeout=86400000000';

        $('#selectEpisode').change(function () {
            location.href = 'http://kissanime.com/Anime/K-On-2-Dub/' + $(this).val();
        });

        $('#selectGroup').change(function () {
            location.href = 'http://kissanime.com/Anime/' + $(this).val();
        });

        if (isHTML5) {
            $('#divContentVideo').html('<video id="my_video_1" class="video-js vjs-default-skin" controls autoplay preload="auto" width="854px" height="552px" data-setup="{}"><source src="' + txha + '" type="video/mp4"></video>');            
            //$('#divContentVideo').html('<div style="position: relative;width:100%;height:100%"><div data-swf="//releases.flowplayer.org/5.4.3/flowplayer.swf" class="flowplayer play-button" style="position: absolute; bottom: 0;" data-embed="false"><video preload="auto" autoplay><source type="video/mp4" src="' + txha + '"/></video></div></div>');
            $('#divTextQua').html('IF THE PLAYER DOES NOT WORK, PLEASE CLICK ON THE URLS BELOW TO WATCH VIDEO');            

                $('#switch').css('left', '860px');
                $('#switch').css('top', '530px');

        }
        else
        {
            //$('#divContentVideo').show();
            setTimeout('DoHideFake()', 2000);
        }

        function DoHideFake()
        {
            $('#divContentVideo').append('<embed id="embedVideo" height="552" src="//www.youtube.com/get_player?enablejsapi=1&modestbranding=1"type="application/x-shockwave-flash" width="854" allowfullscreen="true" allowscriptaccess="always" bgcolor="#fff" scale="noScale" wmode="opaque" flashvars="' + txha + '" style="width: 854px; height: 552px" />');
        }

        function NextEps() {
            $('#divMsg').css('display', 'block');
        }

    </script>

A:

No seu código está removendo o cookie, a data é para forçar a remoção. 

• useHTML5 = ''
  • expires = Thu, 01 Jan 1970 00:00:01

Ou seja, useHTML5 sem um valor atribuido - nulo, e a data do cookie já vencida. 
Neste caso o cookie simplesmente é apagado. 
Por que definir a data em 1970? 

A data Thu, 01 Jan 1970 00:00:01 garante que seja feita a remoção do cookie, mesmo que a data do computados do usuário não seja a data corrente.  Caso o usuário altere a data do PC, 1970 garante a remoção sem conflito de data. 

Um exemplo para a criação de cookie com validade até o final do ano. 
document.cookie="username=John Doe; expires=Thu, 18 Dec 2014 12:00:00 GMT";

[referencia]

A URL do googlevideo provavelmente faz o load dos controles do player.