mirror of
https://github.com/shaka-project/shaka-player.git
synced 2026-06-15 16:06:41 +03:00
Leandro Moreira
111 lines
3.8 KiB
HTML
111 lines
3.8 KiB
HTML
<!--
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Copyright 2014 Google Inc.
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<h3 class="tutorial-heading">
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DASH Streams at a High Level
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</h3>
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<p>
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Dynamic Adaptive Streaming over HTTP (DASH) is a technique for adaptive bitrate
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streaming of content over the Internet delivered from conventional web servers.
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This is a quick overview of DASH for those who are not familiar with it. For a
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more detailed view of DASH, visit {@link http://dashif.org/guidelines/ dashif.org}.
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</p>
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<p>
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Every DASH stream is described by a manifest written in XML. Within a manifest
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file, representation elements describe the DASH stream's audio, video, and text
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sources. There may be more than one representation of the same content. These
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typically differ in terms of bitrate and resolution, although there can be some
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other variations as well.
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</p>
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<p>
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Representations are grouped into one or more adaptation sets, and a DASH client
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can switch automatically between representations within a set. Adaptation sets
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can differ in codec and language. DASH streams usually have audio and video in
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separate adaptation sets. Although the DASH specification allows for audio and
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video to be multiplexed, the Shaka Player does not support this type of stream.
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</p>
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<h3 class="tutorial-heading">
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Multiple Resolutions and Bitrates
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</h3>
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<p>
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For the Shaka Player to adapt and choose the best representation for the user's
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available bandwidth, you must encode your content into more than one resolution
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and bitrate. It is up to you what bitrates and resolutions make sense for your
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site. Note that you can encode at multiple bitrates for a single resolution.
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</p>
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<p>
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Example video encoding scheme:
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<ul>
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<li>1920x1080, 5.0 Mbit/s</li>
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<li>1920x1080, 3.0 Mbit/s</li>
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<li>1280x720, 2.0 Mbit/s</li>
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<li>1280x720, 1.0 Mbit/s</li>
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<li>854x480, 750 kbit/s</li>
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<li>640x360, 350 kbit/s</li>
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</ul>
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</p>
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<p>
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There are many open-source tools to transcode video, including:
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<ul>
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<li>ffmpeg <a href="https://www.ffmpeg.org/">https://www.ffmpeg.org/</a></li>
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<li>DASHEncoder <a href="https://github.com/slederer/DASHEncoder">https://github.com/slederer/DASHEncoder</a></li>
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</ul>
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</p>
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<h3 class="tutorial-heading">
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Packaging Content
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</h3>
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<p>
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A DASH packager is required to get your media ready to stream. There are a few
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open-source packagers available for MP4 / ISO BMFF streams, including:
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<ul>
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<li>edash-packager <a href="https://github.com/google/edash-packager/">https://github.com/google/edash-packager/</a></li>
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<li>MP4Box <a href="http://gpac.wp.mines-telecom.fr/mp4box/">http://gpac.wp.mines-telecom.fr/mp4box/</a></li>
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<li>DASHEncoder <a href="https://github.com/slederer/DASHEncoder">https://github.com/slederer/DASHEncoder</a></li>
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<li>DASH.encrypt <a href="https://github.com/castlabs/dashencrypt">https://github.com/castlabs/dashencrypt</a></li>
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</ul>
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</p>
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<p>
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Your DASH packager will convert your content to a valid, segmented ISOBMFF file
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and generate a DASH manifest (MPD file). Most DASH packagers can not transcode
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your media into multiple resolutions and bitrates. (DASHEncoder does both.)
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</p>
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<p>
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To package WebM streams for DASH, the WebM project provides tools for this:
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<ul>
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<li>webm-tools <a href="http://www.webmproject.org/code/">http://www.webmproject.org/code/</a></li>
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</ul>
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The WebM project also provides <a href="http://goo.gl/cfJ2x3">a tutorial</a> on
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encoding WebM content for DASH.
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</p>
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