103 lines
4.2 KiB
ReStructuredText
103 lines
4.2 KiB
ReStructuredText
####################################
|
|
Low Latency DASH (LL-DASH) Streaming
|
|
####################################
|
|
|
|
************
|
|
Introduction
|
|
************
|
|
|
|
If ``--low_latency_dash_mode`` is enabled, low latency DASH (LL-DASH) packaging will be used.
|
|
|
|
This will reduce overall latency by ensuring that the media segments are chunk encoded and delivered via an aggregating response.
|
|
The combination of these features will ensure that overall latency can be decoupled from the segment duration.
|
|
For low latency to be achieved, the output of Shaka Packager must be combined with a delivery system which can chain together a set of aggregating responses, such as chunked transfer encoding under HTTP/1.1 or a HTTP/2 or HTTP/3 connection.
|
|
The output of Shaka Packager must be played with a DASH client that understands the availabilityTimeOffset MPD value.
|
|
Furthermore, the player should also understand the throughput estimation and ABR challenges that arise when operating in the low latency regime.
|
|
|
|
This tutorial covers LL-DASH packaging and uses features from the DASH, HTTP upload, and FFmpeg piping tutorials.
|
|
For more information on DASH, see :doc:`dash`; for HTTP upload, see :doc:`http_upload`;
|
|
for FFmpeg piping, see :doc:`ffmpeg_piping`;
|
|
for full documentation, see :doc:`/documentation`.
|
|
|
|
*************
|
|
Documentation
|
|
*************
|
|
|
|
Getting started
|
|
===============
|
|
|
|
To enable LL-DASH mode, set the ``--low_latency_dash_mode`` flag to ``true``.
|
|
|
|
All HTTP requests will use chunked transfer encoding:
|
|
``Transfer-Encoding: chunked``.
|
|
|
|
.. note::
|
|
|
|
Only LL-DASH is supported. LL-HLS support is yet to come.
|
|
|
|
Synopsis
|
|
========
|
|
|
|
Here is a basic example of the LL-DASH support.
|
|
The LL-DASH setup borrows features from "FFmpeg piping" and "HTTP upload",
|
|
see :doc:`ffmpeg_piping` and :doc:`http_upload`.
|
|
|
|
Define UNIX pipe to connect ffmpeg with packager::
|
|
|
|
export PIPE=/tmp/bigbuckbunny.fifo
|
|
mkfifo ${PIPE}
|
|
|
|
Acquire and transcode RTMP stream::
|
|
|
|
ffmpeg -fflags nobuffer -threads 0 -y \
|
|
-i rtmp://184.72.239.149/vod/mp4:bigbuckbunny_450.mp4 \
|
|
-pix_fmt yuv420p -vcodec libx264 -preset:v superfast -acodec aac \
|
|
-f mpegts pipe: > ${PIPE}
|
|
|
|
Configure and run packager::
|
|
|
|
# Define upload URL
|
|
export UPLOAD_URL=http://localhost:6767/ll-dash
|
|
|
|
# Go
|
|
packager \
|
|
"input=${PIPE},stream=audio,init_segment=${UPLOAD_URL}_init.m4s,segment_template=${UPLOAD_URL}/bigbuckbunny-audio-aac-\$Number%04d\$.m4s" \
|
|
"input=${PIPE},stream=video,init_segment=${UPLOAD_URL}_init.m4s,segment_template=${UPLOAD_URL}/bigbuckbunny-video-h264-450-\$Number%04d\$.m4s" \
|
|
--io_block_size 65536 \
|
|
--segment_duration 2 \
|
|
--low_latency_dash_mode=true \
|
|
--utc_timings "urn:mpeg:dash:utc:http-xsdate:2014"="https://time.akamai.com/?iso" \
|
|
--mpd_output "${UPLOAD_URL}/bigbuckbunny.mpd" \
|
|
|
|
|
|
*************************
|
|
Low Latency Compatibility
|
|
*************************
|
|
|
|
For low latency to be achieved, the processes handling Shaka Packager's output, such as the server and player,
|
|
must support LL-DASH streaming.
|
|
|
|
Delivery Pipeline
|
|
=================
|
|
Shaka Packager will upload the LL-DASH content to the specified output via HTTP chunked transfer encoding.
|
|
The server must have the ability to handle this type of request. If using a proxy or shim for cloud authentication,
|
|
these services must also support HTTP chunked transfer encoding.
|
|
|
|
Examples of supporting content delivery systems:
|
|
|
|
* `AWS MediaStore <https://aws.amazon.com/mediastore/>`_
|
|
* `s3-upload-proxy <https://github.com/fsouza/s3-upload-proxy>`_
|
|
* `Streamline Low Latency DASH preview <https://github.com/streamlinevideo/low-latency-preview>`_
|
|
* `go-chunked-streaming-server <https://github.com/mjneil/go-chunked-streaming-server>`_
|
|
|
|
Player
|
|
======
|
|
The player must support LL-DASH playout.
|
|
LL-DASH requires the player to be able to interpret ``availabilityTimeOffset`` values from the DASH MPD.
|
|
The player should also recognize the the throughput estimation and ABR challenges that arise with low latency streaming.
|
|
|
|
Examples of supporting players:
|
|
|
|
* `Shaka Player <https://github.com/google/shaka-player>`_
|
|
* `dash.js <https://github.com/Dash-Industry-Forum/dash.js>`_
|
|
* `Streamline Low Latency DASH preview <https://github.com/streamlinevideo/low-latency-preview>`_ |