125 lines
3.8 KiB
ReStructuredText
125 lines
3.8 KiB
ReStructuredText
Media Encoding
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--------------
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Shaka Packager does not do transcoding internally. The contents need to be
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pre-encoded before passing to Shaka Packager.
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General guidelines of how contents should be encoded
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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- 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.
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- 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.
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- 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.
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- In the same stream, the bitrate should be more or less the same in the
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inter-GOP level.
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Sample commands to generate multi-bitrate content
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Let us say we have a 1080p original content `original.mp4` containing an audio
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track in `AAC` and a video track in `H264`. 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.
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We use `ffmpeg <https://www.ffmpeg.org/>`_ here, which is a common tool used for
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transcoding.
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H264 encoding
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"""""""""""""
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* 360p::
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$ 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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* 480p::
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$ 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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* 720p::
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$ 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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* 1080p::
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$ 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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VP9 encoding
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""""""""""""
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The audio is encoded into `opus`.
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* 360p::
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$ 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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* 480p::
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$ 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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* 720p::
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$ 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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* 1080p::
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$ 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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