ABR and Transcoding
Last updated
Last updated
OvenMediaEngine has a built-in live transcoder. The live transcoder can decode the incoming live source and re-encode it with the set codec or adjust the quality to encode at multiple bitrates.
Type | Codec |
---|---|
Type | Codec | Codec of Configuration |
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The <OutputProfile>
setting allows incoming streams to be re-encoded via the <Encodes>
setting to create a new output stream. The name of the new output stream is determined by the rules set in <OutputStreamName>
, and the newly created stream can be used according to the streaming URL format.
According to the above setting, if the incoming stream name is stream
, the output stream becomes stream_bypass
and the stream URL can be used as follows.
WebRTC
ws://192.168.0.1:3333/app/stream_bypass
LLHLS
http://192.168.0.1:8080/app/stream_bypass/llhls.m3u8
HLS
http://192.168.0.1:8080/app/stream_bypass/ts:playlist.m3u8
You can set the video profile as below:
The meaning of each property is as follows:
* required
Table of presets
A table in which presets provided for each codec library are mapped to OvenMediaEngine presets. Slow presets are of good quality and use a lot of resources, whereas Fast presets have lower quality and better performance. It can be set according to your own system environment and service purpose.
References
https://trac.ffmpeg.org/wiki/Encode/VP8
https://docs.nvidia.com/video-technologies/video-codec-sdk/nvenc-preset-migration-guide/
You can set the audio profile as below:
The meaning of each property is as follows:
* required
It is possible to have an audio only output profile by specifying the Audio profile and omitting a Video one.
You can set the Image profile as below:
The meaning of each property is as follows:
The image encoding profile is only used by thumbnail publishers. and, bypass option is not supported.
You can configure Video and Audio to bypass transcoding as follows:
You need to consider codec compatibility with some browsers. For example, chrome only supports OPUS codec for audio to play WebRTC stream. If you set to bypass incoming audio, it can't play on chrome.
WebRTC doesn't support AAC, so if video bypasses transcoding, audio must be encoded in OPUS.
If the codec or quality of the input stream is the same as the profile to be encoded into the output stream. there is no need to perform re-transcoding while unnecessarily consuming a lot of system resources. If the quality of the input track matches all the conditions of BypassIfMatch, it will be Pass-through without encoding
* eq: equal to / lte: less than or equal to / gte: greater than or equal to
* eq: equal to / lte: less than or equal to / gte: greater than or equal to
To support WebRTC and LLHLS, AAC and Opus codecs must be supported at the same time. Use the settings below to reduce unnecessary audio encoding.
If a video track with a lower quality than the encoding option is input, unnecessary upscaling can be prevented. SAR (Storage Aspect Ratio) is the ratio of original pixels. In the example below, even if the width and height of the original video are smaller than or equal to the width and height set in the encoding option, if the ratio is different, it means that encoding is performed without bypassing.
If you want to transcode with the same quality as the original. See the sample below for possible parameters that OME supports to keep original. If you remove the Width, Height, Framerate, Samplerate, and Channel parameters. then, It is transcoded with the same options as the original.
To change the video resolution when transcoding, use the values of width and height in the Video encode option. If you don't know the resolution of the original, it will be difficult to keep the aspect ratio after transcoding. Please use the following methods to solve these problems. For example, if you input only the Width value in the Video encoding option, the Height value is automatically generated according to the ratio of the original video.
The software decoder uses 2 threads by default. If the CPU speed is too low for decoding, increasing the thread count can improve performance.
For use cases without video (re)encoding, OME can be set to only decode the keyframes of incoming streams. This is a massive performance increase when all you are using the encoder for is generating thumbnails.
To set OME to only decode keyframes, all of your encoder Output Profiles must be set to true set true.
Supported since OvenmediaEngine version 0.18.0
From version 0.14.0, OvenMediaEngine can encode same source with multiple bitrates renditions and deliver it to the player.
As shown in the example configuration below, you can provide ABR by adding <Playlists>
to <OutputProfile>
. There can be multiple playlists, and each playlist can be accessed with <FileName>
.
The method to access the playlist set through LLHLS is as follows.
http[s]://<domain>[:port]/<app>/<stream>/
<FileName>
.m3u8
The method to access the playlist set through HLS is as follows.
http[s]://<domain>[:port]/<app>/<stream>/
<FileName>
.m3u8?format=ts
The method to access the Playlist set through WebRTC is as follows.
ws[s]://<domain>[:port]/<app>/<stream>/
<FileName>
Note that <FileName>
must never contain the playlist
and chunklist
keywords. This is a reserved word used inside the system.
To set up <Rendition>
, you need to add <Name>
to the elements of <Encodes>
. Connect the set <Name>
into <Rendition><Video>
or <Rendition><Audio>
.
In the example below, three quality renditions are provided and the URL to play the abr
playlist as LLHLS is https://domain:port/app/stream/abr.m3u8
and The WebRTC playback URL is wss://domain:port/app/stream/abr
TS files used in HLS must have A/V pre-muxed, so the EnableTsPackaging
option must be set in the Playlist.
Even if you set up multiple codecs, there is a codec that matches each streaming protocol supported by OME, so it can automatically select and stream codecs that match the protocol. However, if you don't set a codec that matches the streaming protocol you want to use, it won't be streamed.
The following is a list of codecs that match each streaming protocol:
Therefore, you set it up as shown in the table. If you want to stream using LLHLS, you need to set up H.264, H.265 and AAC, and if you want to stream using WebRTC, you need to set up Opus.
Also, if you are going to use WebRTC on all platforms, you need to configure both VP8 and H.264. This is because different codecs are supported for each browser, for example, VP8 only, H264 only, or both.
However, don't worry. If you set the codecs correctly, OME automatically sends the stream of codecs requested by the browser.
Property | Description |
---|---|
Presets | openh264 | h264_nvenc | h264_qsv | vp8 |
---|---|---|---|---|
Property | Description |
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Property | Description |
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Elements | Condition | Description |
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Elements | Condition | Description |
---|---|---|
Protocol | Supported Codec |
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