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