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<li><a class="reference internal" href="#">Media Encoding</a><ul>
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<li><a class="reference internal" href="#general-guidelines-of-how-contents-should-be-encoded">General guidelines of how contents should be encoded</a></li>
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<li><a class="reference internal" href="#sample-commands-to-generate-multi-bitrate-content">Sample commands to generate multi-bitrate content</a><ul>
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<li><a class="reference internal" href="#h264-encoding">H264 encoding</a></li>
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<li><a class="reference internal" href="#vp9-encoding">VP9 encoding</a></li>
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<div class="section" id="media-encoding">
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<h1>Media Encoding<a class="headerlink" href="#media-encoding" title="Permalink to this headline">¶</a></h1>
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<p>Shaka Packager does not do transcoding internally. The contents need to be
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pre-encoded before passing to Shaka Packager.</p>
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<div class="section" id="general-guidelines-of-how-contents-should-be-encoded">
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<h2>General guidelines of how contents should be encoded<a class="headerlink" href="#general-guidelines-of-how-contents-should-be-encoded" title="Permalink to this headline">¶</a></h2>
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<ul class="simple">
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<li>Encode multiple bitrates or resolutions of the same content. Shaka Packager
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can then package the content into DASH / HLS formats, allowing different
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bitrates of the content to be served for different network conditions,
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achieving adaptive bitrate streaming.</li>
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<li>Not a must, but the multibirate content is recommended to have aligned GOPs
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across the different bitrate streams. This makes bitrate switching easier and
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smoother.</li>
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<li>We recommend setting GOP size to 5s or less. The streams are usually
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switchable only at GOP boundaries. A smaller GOP size results in faster
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switching when network condition changes.</li>
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<li>In the same stream, the bitrate should be more or less the same in the
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inter-GOP level.</li>
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</ul>
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</div>
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<div class="section" id="sample-commands-to-generate-multi-bitrate-content">
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<h2>Sample commands to generate multi-bitrate content<a class="headerlink" href="#sample-commands-to-generate-multi-bitrate-content" title="Permalink to this headline">¶</a></h2>
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<p>Let us say we have a 1080p original content <cite>original.mp4</cite> containing an audio
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track in <cite>AAC</cite> and a video track in <cite>H264</cite>. The frame rate is 24. We want to
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encode the contents into four resolutions: 360p, 480p, 720p and 1080p with GOP
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size 72, i.e. 3 seconds.</p>
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<p>We use <a class="reference external" href="https://www.ffmpeg.org/">ffmpeg</a> here, which is a common tool used for
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transcoding.</p>
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<div class="section" id="h264-encoding">
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<h3>H264 encoding<a class="headerlink" href="#h264-encoding" title="Permalink to this headline">¶</a></h3>
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<ul>
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<li><p class="first">360p:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span>$ ffmpeg -i original.mp4 -c:a copy \
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-vf "scale=-2:360" \
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-c:v libx264 -profile:v baseline -level:v 3.0 \
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-x264opts scenecut=0:open_gop=0:min-keyint=72:keyint=72 \
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-minrate 600k -maxrate 600k -bufsize 600k -b:v 600k \
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-y h264_baseline_360p_600.mp4
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</pre></div>
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</div>
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</li>
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<li><p class="first">480p:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span>$ ffmpeg -i original.mp4 -c:a copy \
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-vf "scale=-2:480" \
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-c:v libx264 -profile:v main -level:v 3.1 \
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-x264opts scenecut=0:open_gop=0:min-keyint=72:keyint=72 \
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-minrate 1000k -maxrate 1000k -bufsize 1000k -b:v 1000k \
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-y h264_main_480p_1000.mp4
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</pre></div>
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</div>
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</li>
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<li><p class="first">720p:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span>$ ffmpeg -i original.mp4 -c:a copy \
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-vf "scale=-2:720" \
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-c:v libx264 -profile:v main -level:v 4.0 \
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-x264opts scenecut=0:open_gop=0:min-keyint=72:keyint=72 \
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-minrate 3000k -maxrate 3000k -bufsize 3000k -b:v 3000k \
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-y h264_main_720p_3000.mp4
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</pre></div>
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</div>
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</li>
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<li><p class="first">1080p:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span>$ ffmpeg -i original.mp4 -c:a copy \
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-vf "scale=-2:1080" \
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-c:v libx264 -profile:v main -level:v 4.2 \
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-x264opts scenecut=0:open_gop=0:min-keyint=72:keyint=72 \
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-minrate 6000k -maxrate 6000k -bufsize 6000k -b:v 6000k \
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-y h264_main_1080p_6000.mp4
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</pre></div>
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</div>
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</li>
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</ul>
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</div>
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<div class="section" id="vp9-encoding">
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<h3>VP9 encoding<a class="headerlink" href="#vp9-encoding" title="Permalink to this headline">¶</a></h3>
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<p>The audio is encoded into <cite>opus</cite>.</p>
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<ul>
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<li><p class="first">360p:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span>$ ffmpeg -i original.mp4 \
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-strict -2 -c:a opus \
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-vf "scale=-2:360" \
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-c:v libvpx-vp9 -profile:v 0 \
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-keyint_min 72 -g 72 \
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-tile-columns 4 -frame-parallel 1 -speed 1 \
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-auto-alt-ref 1 -lag-in-frames 25 \
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-b:v 300k \
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-y vp9_360p_300.webm
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</pre></div>
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</div>
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</li>
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<li><p class="first">480p:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span>$ ffmpeg -i original.mp4 \
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-strict -2 -c:a opus \
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-vf "scale=-2:480" \
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-c:v libvpx-vp9 -profile:v 0 \
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-keyint_min 72 -g 72 \
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-tile-columns 4 -frame-parallel 1 -speed 1 \
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-auto-alt-ref 1 -lag-in-frames 25 \
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-b:v 500k \
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-y vp9_480p_500.webm
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</pre></div>
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</div>
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</li>
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<li><p class="first">720p:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span>$ ffmpeg -i original.mp4 \
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-strict -2 -c:a opus \
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-vf "scale=-2:720" \
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-c:v libvpx-vp9 -profile:v 0 \
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-keyint_min 72 -g 72 \
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-tile-columns 4 -frame-parallel 1 -speed 1 \
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-auto-alt-ref 1 -lag-in-frames 25 \
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-b:v 1500k \
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-y vp9_720p_1500.webm
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</pre></div>
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</div>
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</li>
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<li><p class="first">1080p:</p>
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<div class="highlight-default"><div class="highlight"><pre><span></span>$ ffmpeg -i original.mp4 \
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-strict -2 -c:a opus \
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-vf "scale=-2:1080" \
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-c:v libvpx-vp9 -profile:v 0 \
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-keyint_min 72 -g 72 \
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-tile-columns 4 -frame-parallel 1 -speed 1 \
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-auto-alt-ref 1 -lag-in-frames 25 \
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-b:v 3000k \
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-y vp9_1080p_3000.webm
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</pre></div>
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</div>
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</li>
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