Bandwidth Considerations

                                                                                                Last Mile                IPS / Carrier Network / CDN  /           Last Mile

Video Capture                    Cable            Video Encode           Upload                  Broadcast Service Platform              Download                Audience

HDMI                                     SDI (Coaxial)

Video Size

240p:426x240

360p:640x360

480p:854x480

720p:1280x720

1080p:1902x1080

1440p (2K);2560x1440

2160p (4K):3480x2160

 

 

 

Bandwidth

Mbps

Bandwidth

Mbps

Ethernet cable

Fiber

3G/4G/5G

Ethernet cable

Fiber

3G/4G/5G Wireless

Latency  (ms)

Audio bitrate

 

       +

 

Video bitrate

x 1.5  =  Required upload bandwidth

2. Checking table for required upload bandwidth for H.265 live streaming

Based on above algorithm with the audio bitrate fixed at 192k/s, we can come up with a table having the required bandwidth for different video size running at 30 f/s and 60f/s using H.265 video format (QF=0.08), please check appendix I

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* Although QF may be considered an inaccurate measure of video compression quality, where it becomes valuable is during the video encoding or transcoding stage. There are several internet forum discussions on the optimum quality that should be used for encoding.  In reality, every video has its own unique and optimum settings.  Information obtained from [1] http://dusil.com/tag/bitrate/

Appendix I:

Codec Comparison for a 1080p @24 f/s video maintaining at the same video quality

1. Checking table for required upload bandwidth for H.264 live streaming

Based on above algorithm with the audio bitrate fixed at 192k/s, we can come up with a table having the required bandwidth for different video size running at 30 f/s and 60f/s using H.264 video format (QF=0.125)

 To keep customers / clients’ attention to eye on your livestream video, one of the important thing is to providing a stable and quality livestream video to them.  To ensure a stable and quality live stream video, we have look into bandwidth of the signal path carefully. 

 

As shown in the following graph, if you want to transmit a video game to show someone in another country, you will have to make sure the video content is uploaded and downloaded within the bandwidth limitation of the signal path.

 

Now let’s use a commonly used approach to calculate the required bandwidth for sending a video with a certain video size.

First let’s calculate how many pixels per second your video would like to present to your audience

 

Pixels per second = Width  x height  x Frames rate

 

For instance if you plan to upload a livestream HD (720p) video to YouTube with a frame rate of 30 Frame/ second.

The pixel per second would be 1280 x 720 x 30= 27,648,000 pixel/ second

 

There is an important factor in video quality defined as Quality Factor QF*.  QF represents a video file compression density, which is also known as Bits per pixel (bpp).  Any bpp values around 0.1 would have pretty good pixel quality for a H.264 video format.  A higher bpp won’t product a significant improvement visually. (very similar to you see a 60 f/s video comparing to a 30 f/s video, we won’t be able to see too much difference.)   However if the bpp value is around 0.03, the video is obvious showing the poor quality video.

 

Now let’s set QF: Bits per pixel (bpp)= 1/8 = 0.125 for a H.264 video stream, and we can find the video bitrate

 

Video bitrate for a HD video = bpp x Pixel per second = 0.125 x 27,648,000 = 3,456K bit per second ~ 3.5 (Mbps)

 

In addition to video we need take account of the audio quality.  A default mono sound audio bitrate is 64K.  If you need quality stereo sound, use 128K or 192K.  (For a home DVD theater system would be better in 320K)

 

If we select audio bit rate at 192K, and then we would be able to find the required upload bandwidth as following

 

 (Video bitrate + Audio bitrate) x 1.5 = (3456 K/s + 192 K/s) x 1.5 = 5,472 K/s  ~ 5.5Mbps  <— ( the required upload bandwidth )

 

 

The number 1.5 times the (video bitrate + audio bitrate) is recommended to taking account of the transmission fluctuations along the signal path to network.