The Broadcast Video option allows users to incorporate HD quality video into Live webcasts. The Broadcast Video option requires external encoding gear to encode the video file at your location before sending the encoded stream to the ON24 platform. The recommended encoders include Wirecast, OBS, VMix, and Elemental, running on machine platforms consistent with those supported by the software. Two such machines, each publishing separate streams, are recommended for redundancy during your webinar.
Note: The Broadcast Video option is available at an additional cost and will need to be enabled for your account. Contact your ON24 Account Executive for more information.
Overview - Streaming Signal Flow to ON24 Ingress Servers
At a venue or auditorium, this would be a common setup. Note that A/V switching and encoding happens onsite.
Step 1 - Create Your Event
First, create a new event by choosing Broadcast Video as the Event Type on the Overview tab.
Once you create a new event with the Broadcast Video present type, Webcast Elite will provide the URL and Stream ID.
The URL and Stream ID need to be inputted into your encoder. For your convenience, Elite offers a copy option for both. You can also download the XML file to open in your encoder.
- Encoder A is required and must be used in order for the webinar archive to process correctly.
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Encoder B is for the backup encoder, it's optional, but playlists will assume it is present.
- As a best practice, it's essential to have a backup encoder set up to avoid a single-point-of-failure.
Notes:
- A Broadcast Video stream must be active for rehearsals or testing features such as polls, highlighting/centering engagement tools, etc. Otherwise, these features will not display.
- The URL and Stream ID are case-sensitive. Please input exactly what is provided. Even a space at the beginning or the end will cause it to fail.
- While ON24 systems record the streams for on-demand use, we recommend your have your encoder save an insurance copy.
Sample Output Settings Using Wirecast
Step 2 - Set Up Your Encoders
The encoders will require an un-proxied outbound connection on TCP port 1935; no proxied transport is supported for the encoded stream transport to the ON24 Ingress server.
RTMPS ingress is supported if your encoder supports it (Elemental and OBS are known to support it). The inbound RTMP stream is received at Ingress servers, then routed to transcoders for HLS (desktop and mobile) streams. The output rates associated with the transcoders are configurable; the "normal" rate is 750k+2500k video for HLS.
Speeds as low as 250k and as high as 2500k are supported and can be configured as needed.
The specs below assume that you will furnish inbound streams at a higher quality than the output speeds.
| Wirecast | |
| Profile | Main |
| Video Format | MainConcept H.264 |
| Frame Rate | For smooth motion, 24, 25, or 30 fps are recommended. Lower frame rates can be used as needed, especially in very limited bandwidth applications. |
| Frame Size | 1280x720 |
| Video Bitrate | 500 kbps or higher, with 2,500 Kbps the most frequently used inbound rate |
| Audio Format | AAC |
| Audio Sample Rate | 48 or 44.1 kHz |
| Audio Bitrate | 64 kbps |
| Constant Bit Rate | Constant Bit Rate is the default. Variable inbound bit rates are associated with various problems, including lip sync issues, and should be avoided. |
| Keyframe Interval | The Keyframe must be 2x the specified frame rate. The segment size is 2 seconds and each segment requires a keyframe (see Sample Wirecast Image) |
Note: Make sure that account settings are configured for this option.
| Wirecast | |
| Profile | Main |
| Video Format | MainConcept H.264 |
| Frame Rate | 30 fps, Constant Frame Rate |
| Frame Size | 1920x1080 |
| Video Bitrate | 5000 Kbps |
| Audio Format | AAC (mono) |
| Audio Sample Rate | 48.0 kHz |
| Audio Bitrate | 96 Kbps |
| Constant Bit Rate | Constant Bit Rate is the default. Variable inbound bit rates are associated with various problems, including lip sync issues, and should be avoided. |
| Keyframe Interval | Keyframe every 2 seconds |
Sample Wirecast Encoder Settings
Step 3 - Previewing the Encoded Video
Previewing the encoded video is recommended before the live webcast to check that your encoder is working properly.
To preview your encoder, start the encoder then use the Preview URL in Elite to open the preview console. It is possible to view the B side streams - to verify that they are active and routed correctly - by appending "&streamtest=y" without the quotation marks to the preview link. This will cause the preview console to display a console that lists the available playlist entries. The "Primary" entries are A side streams, backup entries are B side streams. HTML5 streams are labeled "Dash Playlist", and Hive or Kollective streams are appropriately labeled. Please see a sample UI below.
DASH streams are those seen on the desktop. Metadata is displayed when the streams are actually playing - the view above is not playing a stream. The bit rate associated with the Audio and Video is reported; it changes as the adjustable bit rate functionality (ABR) causes video speeds to step up or down. HLS (mobile) console is not supported by "stream test" mode.
Tip: The video media window in the audience console defaults to a 16:9 ratio. If you are using 4:3 video, be sure to go to the Console Builder and change the size of the video window to match the 16:9 ratio.
Step 4 - Running the Live Webcast
When it comes time for the live webcast, the following timeline is required:
- Start your encoder before audience lobby open time.
- The audience will be able to see the event console 15 minutes before the event start time, so you should start the encoder one hour before this to allow time for problems to be resolved if any arise.
- If the encoder is started after the audience console is launched, the audience will need to refresh their console (F5 for Windows / Command + R for Macs) for the encoded video stream to appear.
- If you need assistance at the event start, contact the Event Emergency Line.
- Click the Start Live button in Elite Studio when ready to begin the webcast, and then click the End Webcast button when the webcast is over.
- Clicking these buttons will enable the auto-archive process.
- The system starts recording at Start Live and stops the recording at End Webcast.
- Start recording for a local archive.
- We recommend creating an "insurance copy" of the encoded video as a backup.
Best Practices
The specs provided here are supported by ON24 processing systems, downstream transcoders for mobile devices, and HLS outputs, CDNs, etc.
If you are knowledgeable, feel free to modify them as you think appropriate. If you need advice as to whether a given change is likely to cause trouble, please submit a case to Platform Support asking whether it matters; we'll try to get you a prompt answer.
If you are new, you can safely use the suggestions, as is. Please inspect the downloadable Wirecast configurations, as version changes can cause nonsensical configurations.
Constant Bit Rate streams should always be used. In Wirecast, check the Strict Constant Bitrate box.
For Platform / technical support options, contact Support.
And see the ON24 Streaming Architecture article to find additional information for well-informed decision making. You may need to understand the way streams are received and transcoded to transform them from the RTMP input to HLS outputs (desktop and mobile).
We deliver 750/2500Kbps to users. 1,000-1,500 kbps encoding is reasonable since the final delivered streams are Adjustable Bit Rate at 750k and 2500k video bit rates.
Bandwidth requirements are a function of several issues:
- Motion on the video- If the speaker is standing still behind a podium, there is much less video load than if they are pacing on a stage. Action in the background (as opposed to curtains, walls, etc.) increases the video load.
- The frame rate directly determines the need for bandwidth. Frame rates less than 24fps allow the eye to see "choppy video" where there is motion. 24fps or greater, and the eye can't see the changes between frames. A non-expert user should never configure for greater than 30 fps. Screen sharing (static images of the entire desktop) is usually done at 10-12 frames per second, trading smooth motion for high resolution of the relatively static screen image.
- If you are very bandwidth-challenged, configure for 300kbps and 15 fps, and ask the speaker to minimize his movement.
- ON24 HLS streams utilize 2-second segments, each of which requires a keyframe. Always configure the encoder to provide a "keyframe every" rate equal to 2 times the fps. So a keyframe every 30 frames for a 15 fps video, or every 60 frames for a 30fps video. For Elemental encoders, specify a GOP of 2 seconds.
- In situations where a video clip (720 or 1280p) is used to show a demo of a computer application - where the content shows is a computer UI with lots of text needing high resolution for the audience to be able to see it - the following is normally a viable solution. Set the frame rate to 15, the bit rate to 2500, and the width/height to 1280/720. The audience will normally enlarge their media player to something close to full screen, so a slower Frame Rate with a larger image is a viable compromise for a good quality viewing experience.
- Always use Constant Bit Rate (in Wirecast, check the "Strict Constant Bit Rate" box), never Variable Bit Rate encoding. VBR can generate very large spikes in bandwidth demand. For bandwidth challenged devices (mobile users are frequently bandwidth challenged), this can cause audio/video sync problems.
In a CBR file, the output bit rate is generally the same - in a much tighter range of values. In a VBR file, the reported bit rate is averaged out over the file, so some parts can potentially have low data rates and some really high data rates.
What happens in a VBR file is that during encoding, the encoder looks at the video file and does determinations to render out each frame at the bit rate (data rate) it thinks is optimal. Unfortunately, this can fluctuate wildly. During areas of extreme motion, rapid content shifts/transitions, if there are certain patterns or color combinations on screen, the encoder will greatly increase the data rate, in order to improve the quality of the video. Because it's looking to average out the data rate over the whole file, this can cause wild data rate fluctuations, which can in turn cause major buffering issues. A lot of VBR files will playback just fine, but it’s a gamble.
Important: Please note that sometimes a file that is actually CBR will register as a VBR file. We create CBR files in Adobe Media Encoder that sometimes read in the metadata as VBR files because there is a small variance in the encoding data rate throughout. If this is happening to the client, they can safely ignore that.
The most important thing is that there are no wild fluctuations in the bit rate of the file. The easiest way to see that is to use a VLC player to playback a file, then look at TOOLS > CODEC INFORMATION > Statistics tab. In the Input/Read Section you will see “Content Bitrate” and you will notice the numbers changing throughout while playing back the file. If that number goes above 2200 kb/s a lot, you are going to have issues.
Please use stream dimensions from the table below. Under no circumstances should either height or width be an odd number - such a configuration has been known to cause problems, especially for mobile devices. Also, using Stereo audio is pointless, because the normal stream processing methods convert the audio to mono in the final step before distribution to the audience. Also, instances have been seen where stereo audio will generate exactly inverse Right and Left channels; when combined, these cancel each other out, yielding a silent audio stream.
Please note, the "Output Stream Dimensions" column refers to the encoded stream output, not to the room set up or input stream. All audio should be sampled at 44.1 or 48kHz. Also, the "Output Stream" size used on the encoder itself should generally be the same as the media player configuration, which is rarely larger than 768x432.
The default data rate for HLS streams (desktop and mobile) are 750/2500kbps video, plus 64k audio served as Adjustable Bit Rate (ABR) streams. These are final delivery rates, not the bit rate at which streams are encoded.
| Output Stream Dimensions | Lowest Total Bit Rate Inbound to ON24 | Typical Total Bit Rate Inbound to ON24 | Suggested Audio Bit Rate |
|---|---|---|---|
| 1280x720 (720p) | 1.2 Mbps | 1.5 Mbps | 96k mono |
| 1024x576 | 1.0 Mbps | 1.2 Mbps | 96k mono |
| 960x540 | 800k | 1.0 Mbps | 96k mono |
| 800x450 | 750k | 800k | 96k mono |
| 768x432 | 650k | 750k | 96k or 64 mono |
| 640x360 | 450k | 500k | 96k or 64 mono |
| 576x324 | 350k | 425k | 96k or 64 mono |
| 512x288 | 300k | 400k | 64k mono |
| 480x270 | 300k | 350k | 64k mono |
| 448x252 | 250k | 300k | 48k mono |
| 384x216 | 200k | 300k | 48k mono |
| 320x180 | 150k | 250k | 32k mono |
| 160x90 | 80k | 100k | 20k mono |
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