MPEG DASH
db20553b1e582ccadd0709e61af6dce2.png由於 HTML5 針對 MPEG Streaming 越來越細緻，也需要做得好，所以紀錄一下研究的結果!
 
MPEG-DASH (Dynamic Adaptive Streaming over HTTP) 是一個可調整 bitrate 的 streaming 技術。透過這樣的技術，可以在收看 streaming 時，針對網路的流量來調整最適合的品質播放。最常見的就是 youtube，如果仔細觀察就會發現，品質是可以根據用戶的網路速度來調整的。如果想要觀察這樣的行為，可以直接用這個網址測試！
 
這樣就可以直接切換不同的頻寬的影片了。
使用 DASH 的好處是，不僅可以切換不同品質的影片，也能夠把聲音跟影像分開！這樣才能夠保證在切換的時候不會造成聲音停頓的問題!
 
 
以下為 MPD 的描述 (這是從 youtube 抓出來的範例)
<?xml version="1.0" encoding="UTF-8"?>
<MPD xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="urn:mpeg:DASH:schema:MPD:2011" xmlns:yt="http://youtube.com/yt/2012/10/10" xsi:schemaLocation="urn:mpeg:DASH:schema:MPD:2011 DASH-MPD.xsd" minBufferTime="PT1.500S" profiles="urn:mpeg:dash:profile:isoff-on-demand:2011" type="static" mediaPresentationDuration="PT20.247S">
    <Period>
        <AdaptationSet mimeType="audio/mp4" subsegmentAlignment="true">
            <Representation id="139" codecs="mp4a.40.5" audioSamplingRate="22050" startWithSAP="1" bandwidth="48543">
                <AudioChannelConfiguration schemeIdUri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011" value="2" />
                <BaseURL yt:contentLength="121199">http://r2---sn-ipoxu-u2xl.googlevideo.com/videoplayback?id=d07c4c2c028c9038&amp;itag=139&amp;source=youtube&amp;playback_host=r2---sn-ipoxu-u2xl.googlevideo.com&amp;cmbypass=yes&amp;ratebypass=yes&amp;gir=yes&amp;clen=121199&amp;lmt=1394420759457149&amp;dur=20.247&amp;key=dg_yt0&amp;sver=3&amp;fexp=900225,906335,932261,916807,934913,916611,937417,913434,936910,936913,934022,3300009,3300100,3300134,3300137,3300161,3310366,3310628,3310649&amp;signature=04E654301557E32F0AED2F7C88D8EC1AA0D58C2B.259AA39F1C2CA6FAC412874E5602A0228F46D59E&amp;ms=au&amp;upn=uM4FwNm82uQ&amp;mt=1394888580&amp;mv=u&amp;mime=audio/mp4&amp;ip=59.120.37.117&amp;ipbits=0&amp;expire=1394913830&amp;sparams=ip,ipbits,expire,id,itag,source,playback_host,cmbypass,ratebypass,gir,clen,lmt,dur</BaseURL>
                <SegmentBase indexRange="593-660" indexRangeExact="true">
                    <Initialization range="0-592" />
                </SegmentBase>
            </Representation>
            <Representation id="140" codecs="mp4a.40.2" audioSamplingRate="44100" startWithSAP="1" bandwidth="127984">
                <AudioChannelConfiguration schemeIdUri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011" value="2" />
                <BaseURL yt:contentLength="321203">http://r2---sn-ipoxu-u2xl.googlevideo.com/videoplayback?id=d07c4c2c028c9038&amp;itag=140&amp;source=youtube&amp;playback_host=r2---sn-ipoxu-u2xl.googlevideo.com&amp;cmbypass=yes&amp;ratebypass=yes&amp;gir=yes&amp;clen=321203&amp;lmt=1394420756531007&amp;dur=20.178&amp;key=dg_yt0&amp;sver=3&amp;fexp=900225,906335,932261,916807,934913,916611,937417,913434,936910,936913,934022,3300009,3300100,3300134,3300137,3300161,3310366,3310628,3310649&amp;signature=0642D22D6615387A3CEE03DA2833747FD8B53F3E.2AA665821C0091ED9C2BF8661819B78518A82C01&amp;ms=au&amp;upn=uM4FwNm82uQ&amp;mt=1394888580&amp;mv=u&amp;mime=audio/mp4&amp;ip=59.120.37.117&amp;ipbits=0&amp;expire=1394913830&amp;sparams=ip,ipbits,expire,id,itag,source,playback_host,cmbypass,ratebypass,gir,clen,lmt,dur</BaseURL>
                <SegmentBase indexRange="592-659" indexRangeExact="true">
                    <Initialization range="0-591" />
                </SegmentBase>
            </Representation>
            <Representation id="141" codecs="mp4a.40.2" audioSamplingRate="44100" startWithSAP="1" bandwidth="257226">
                <AudioChannelConfiguration schemeIdUri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011" value="2" />
                <BaseURL yt:contentLength="644053">http://r2---sn-ipoxu-u2xl.googlevideo.com/videoplayback?id=d07c4c2c028c9038&amp;itag=141&amp;source=youtube&amp;playback_host=r2---sn-ipoxu-u2xl.googlevideo.com&amp;cmbypass=yes&amp;ratebypass=yes&amp;gir=yes&amp;clen=644053&amp;lmt=1394420761566193&amp;dur=20.178&amp;key=dg_yt0&amp;sver=3&amp;fexp=900225,906335,932261,916807,934913,916611,937417,913434,936910,936913,934022,3300009,3300100,3300134,3300137,3300161,3310366,3310628,3310649&amp;signature=0BFF77525D8353C7735BC967284BF2AFEA16BDF7.46CA0B5D897178172D8D604EE08C10D61C136B39&amp;ms=au&amp;upn=uM4FwNm82uQ&amp;mt=1394888580&amp;mv=u&amp;mime=audio/mp4&amp;ip=59.120.37.117&amp;ipbits=0&amp;expire=1394913830&amp;sparams=ip,ipbits,expire,id,itag,source,playback_host,cmbypass,ratebypass,gir,clen,lmt,dur</BaseURL>
                <SegmentBase indexRange="592-659" indexRangeExact="true">
                    <Initialization range="0-591" />
                </SegmentBase>
            </Representation>
        </AdaptationSet>
 
        <AdaptationSet mimeType="audio/webm" subsegmentAlignment="true">
            <Representation id="171" codecs="vorbis" audioSamplingRate="44100" startWithSAP="1" bandwidth="116267">
                <AudioChannelConfiguration schemeIdUri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011" value="2" />
                <BaseURL yt:contentLength="290465">http://r2---sn-ipoxu-u2xl.googlevideo.com/videoplayback?id=d07c4c2c028c9038&amp;itag=171&amp;source=youtube&amp;playback_host=r2---sn-ipoxu-u2xl.googlevideo.com&amp;cmbypass=yes&amp;ratebypass=yes&amp;gir=yes&amp;clen=290465&amp;lmt=1394606562936146&amp;dur=20.119&amp;key=dg_yt0&amp;sver=3&amp;fexp=900225,906335,932261,916807,934913,916611,937417,913434,936910,936913,934022,3300009,3300100,3300134,3300137,3300161,3310366,3310628,3310649&amp;signature=4F8183B2B00302AB2F35B1F44783B819BB3DC7A1.44E7B754448FC98706E2562ED5C7B3BB7335FA0F&amp;ms=au&amp;upn=uM4FwNm82uQ&amp;mt=1394888580&amp;mv=u&amp;mime=audio/webm&amp;ip=59.120.37.117&amp;ipbits=0&amp;expire=1394913830&amp;sparams=ip,ipbits,expire,id,itag,source,playback_host,cmbypass,ratebypass,gir,clen,lmt,dur</BaseURL>
                <SegmentBase indexRange="4452-4502" indexRangeExact="true">
                    <Initialization range="0-4451" />
                </SegmentBase>
            </Representation>
            <Representation id="172" codecs="vorbis" audioSamplingRate="44100" startWithSAP="1" bandwidth="166147">
                <AudioChannelConfiguration schemeIdUri="urn:mpeg:dash:23003:3:audio_channel_configuration:2011" value="2" />
                <BaseURL yt:contentLength="401392">http://r2---sn-ipoxu-u2xl.googlevideo.com/videoplayback?id=d07c4c2c028c9038&amp;itag=172&amp;source=youtube&amp;playback_host=r2---sn-ipoxu-u2xl.googlevideo.com&amp;cmbypass=yes&amp;ratebypass=yes&amp;gir=yes&amp;clen=401392&amp;lmt=1394606560692748&amp;dur=20.119&amp;key=dg_yt0&amp;sver=3&amp;fexp=900225,906335,932261,916807,934913,916611,937417,913434,936910,936913,934022,3300009,3300100,3300134,3300137,3300161,3310366,3310628,3310649&amp;signature=8D23DF20959C7A4D34CDA2A2FC1AF8291A64F039.2FA6A24FEDA8CEB8A75675AD2BDF88F68EE6FBA0&amp;ms=au&amp;upn=uM4FwNm82uQ&amp;mt=1394888580&amp;mv=u&amp;mime=audio/webm&amp;ip=59.120.37.117&amp;ipbits=0&amp;expire=1394913830&amp;sparams=ip,ipbits,expire,id,itag,source,playback_host,cmbypass,ratebypass,gir,clen,lmt,dur</BaseURL>
                <SegmentBase indexRange="3995-4045" indexRangeExact="true">
                    <Initialization range="0-3994" />
                </SegmentBase>
            </Representation>
        </AdaptationSet>
 
 
        <AdaptationSet mimeType="video/mp4" subsegmentAlignment="true">
            <Representation id="133" codecs="avc1.4d4015" width="426" height="240" startWithSAP="1" bandwidth="247149">
                <BaseURL yt:contentLength="614054">http://r2---sn-ipoxu-u2xl.googlevideo.com/videoplayback?id=d07c4c2c028c9038&amp;itag=133&amp;source=youtube&amp;playback_host=r2---sn-ipoxu-u2xl.googlevideo.com&amp;cmbypass=yes&amp;ratebypass=yes&amp;gir=yes&amp;clen=614054&amp;lmt=1394420761538993&amp;dur=20.086&amp;key=dg_yt0&amp;sver=3&amp;fexp=900225,906335,932261,916807,934913,916611,937417,913434,936910,936913,934022,3300009,3300100,3300134,3300137,3300161,3310366,3310628,3310649&amp;signature=4E357B9A55A04C460F3AEBDD1B6327DA0DA082CD.8CABCF9A9A6417D0D6D3F62F53C4E7ADD7F7267D&amp;ms=au&amp;upn=uM4FwNm82uQ&amp;mt=1394888580&amp;mv=u&amp;mime=video/mp4&amp;ip=59.120.37.117&amp;ipbits=0&amp;expire=1394913830&amp;sparams=ip,ipbits,expire,id,itag,source,playback_host,cmbypass,ratebypass,gir,clen,lmt,dur</BaseURL>
                <SegmentBase indexRange="677-756" indexRangeExact="true">
                    <Initialization range="0-676" />
                </SegmentBase>
            </Representation>
            <Representation id="134" codecs="avc1.4d401e" width="640" height="360" startWithSAP="1" bandwidth="423848">
                <BaseURL yt:contentLength="899260">http://r2---sn-ipoxu-u2xl.googlevideo.com/videoplayback?id=d07c4c2c028c9038&amp;itag=134&amp;source=youtube&amp;playback_host=r2---sn-ipoxu-u2xl.googlevideo.com&amp;cmbypass=yes&amp;ratebypass=yes&amp;gir=yes&amp;clen=899260&amp;lmt=1394420760590263&amp;dur=20.086&amp;key=dg_yt0&amp;sver=3&amp;fexp=900225,906335,932261,916807,934913,916611,937417,913434,936910,936913,934022,3300009,3300100,3300134,3300137,3300161,3310366,3310628,3310649&amp;signature=084DF8E6E22F75E443389CF79AE1936648FF2F02.1BFD4C1C27275FF36626A653C09054E9B82B0758&amp;ms=au&amp;upn=uM4FwNm82uQ&amp;mt=1394888580&amp;mv=u&amp;mime=video/mp4&amp;ip=59.120.37.117&amp;ipbits=0&amp;expire=1394913830&amp;sparams=ip,ipbits,expire,id,itag,source,playback_host,cmbypass,ratebypass,gir,clen,lmt,dur</BaseURL>
                <SegmentBase indexRange="709-788" indexRangeExact="true">
                    <Initialization range="0-708" />
                </SegmentBase>
            </Representation>
            <Representation id="135" codecs="avc1.4d401f" width="854" height="480" startWithSAP="1" bandwidth="803225">
                <BaseURL yt:contentLength="1760282">http://r2---sn-ipoxu-u2xl.googlevideo.com/videoplayback?id=d07c4c2c028c9038&amp;itag=135&amp;source=youtube&amp;playback_host=r2---sn-ipoxu-u2xl.googlevideo.com&amp;cmbypass=yes&amp;ratebypass=yes&amp;gir=yes&amp;clen=1760282&amp;lmt=1394420767493544&amp;dur=20.086&amp;key=dg_yt0&amp;sver=3&amp;fexp=900225,906335,932261,916807,934913,916611,937417,913434,936910,936913,934022,3300009,3300100,3300134,3300137,3300161,3310366,3310628,3310649&amp;signature=45A2F7C4D3BCE064778FDC34FDDB9162B780936C.57660A6974A7DCA5BF67439F83DF0375BA5BE355&amp;ms=au&amp;upn=uM4FwNm82uQ&amp;mt=1394888580&amp;mv=u&amp;mime=video/mp4&amp;ip=59.120.37.117&amp;ipbits=0&amp;expire=1394913830&amp;sparams=ip,ipbits,expire,id,itag,source,playback_host,cmbypass,ratebypass,gir,clen,lmt,dur</BaseURL>
                <SegmentBase indexRange="713-792" indexRangeExact="true">
                    <Initialization range="0-712" />
                </SegmentBase>
            </Representation>
            <Representation id="160" codecs="avc1.42c00c" width="256" height="144" startWithSAP="1" bandwidth="114177">
                <BaseURL yt:contentLength="283175">http://r2---sn-ipoxu-u2xl.googlevideo.com/videoplayback?id=d07c4c2c028c9038&amp;itag=160&amp;source=youtube&amp;playback_host=r2---sn-ipoxu-u2xl.googlevideo.com&amp;cmbypass=yes&amp;ratebypass=yes&amp;gir=yes&amp;clen=283175&amp;lmt=1394420763553808&amp;dur=20.086&amp;key=dg_yt0&amp;sver=3&amp;fexp=900225,906335,932261,916807,934913,916611,937417,913434,936910,936913,934022,3300009,3300100,3300134,3300137,3300161,3310366,3310628,3310649&amp;signature=4E4BDAC3F2EBAD217601F24ABF185D160F861B67.20AF456A1C5E0474BA04A57817C1707E0764479F&amp;ms=au&amp;upn=uM4FwNm82uQ&amp;mt=1394888580&amp;mv=u&amp;mime=video/mp4&amp;ip=59.120.37.117&amp;ipbits=0&amp;expire=1394913830&amp;sparams=ip,ipbits,expire,id,itag,source,playback_host,cmbypass,ratebypass,gir,clen,lmt,dur</BaseURL>
                <SegmentBase indexRange="672-751" indexRangeExact="true">
                    <Initialization range="0-671" />
                </SegmentBase>
            </Representation>
            <Representation id="136" codecs="avc1.4d401f" width="1280" height="720" startWithSAP="1" bandwidth="1539482">
                <BaseURL yt:contentLength="3508736">http://r2---sn-ipoxu-u2xl.googlevideo.com/videoplayback?id=d07c4c2c028c9038&amp;itag=136&amp;source=youtube&amp;playback_host=r2---sn-ipoxu-u2xl.googlevideo.com&amp;cmbypass=yes&amp;ratebypass=yes&amp;gir=yes&amp;clen=3508736&amp;lmt=1394420776544869&amp;dur=20.086&amp;key=dg_yt0&amp;sver=3&amp;fexp=900225,906335,932261,916807,934913,916611,937417,913434,936910,936913,934022,3300009,3300100,3300134,3300137,3300161,3310366,3310628,3310649&amp;signature=2394AF11A0C86E9D359D654162ADB4569F551060.6BE517FB3326C126D40FB565D0794A7F49C2A7FB&amp;ms=au&amp;upn=uM4FwNm82uQ&amp;mt=1394888580&amp;mv=u&amp;mime=video/mp4&amp;ip=59.120.37.117&amp;ipbits=0&amp;expire=1394913830&amp;sparams=ip,ipbits,expire,id,itag,source,playback_host,cmbypass,ratebypass,gir,clen,lmt,dur</BaseURL>
                <SegmentBase indexRange="709-788" indexRangeExact="true">
                    <Initialization range="0-708" />
                </SegmentBase>
            </Representation>
        </AdaptationSet>
    </Period>
</MPD>
 

註解

  1. 圖片引用來源: http://www.streamingmedia.com
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