How do I configure dual video tracks?-Real-Time Communication(RTC)-阿里云帮助中心

Alibaba Cloud Real-Time Communication (RTC) supports the dual-track mode, in which a major track and a minor track exist. You can enable this feature based on your business requirements. This topic describes the implementation method and specifications of dual video tracks. iOS is used as an example.

Implementation method

In multi-user video communication, you can call setVideoEncoderConfiguration to reduce the video resolution and bitrate at the publishing end, or call publishLocalDualStream to enable the dual-track mode and call setRemoteVideoStreamType to subscribe to the minor track by default. This reduces the resource consumption of coding and relieves the downstream bandwidth pressure. For more information, see Configure video attributes.

Note After the dual-track mode is enabled, RTC SDK pushes an additional video track with lower resolution and bitrate. The original video track is called a major track, and the low-resolution, low-bitrate video track is called a minor track.

Default mappings of dual-track specifications

RTC SDK automatically sets the default specifications of the minor track based on the specifications of the major track. The following table describes the mappings.

Aspect ratio (width:height) of the major track	Minor track
Aspect ratio (width:height) of the major track	Resolution (width × height)	Bitrate (unit: Kbit/s)	Frame rate (unit: fps)
1:1	160 × 160	100	10
3:4	120 × 160	100	10
4:3	160 × 120	100	10
9:16	90 × 160	100	10
16:9	160 × 90	100	10
Other aspect ratios	The greater of the width and height of a minor track is 160. The smaller of the two is calculated based on the ratio.	100	10

Note The default specifications of the minor track follow the following rules:

The greater of the width and height of a minor track is fixed at 160. The aspect ratio of a minor track is the same as that of the corresponding major track.
The frame rate of the minor track is fixed at 10 fps.
The width and height of the minor track must be even numbers.
The bitrate of the minor track is fixed at 100 Kbit/s.

Customize minor track specifications

To customize minor track specifications, you can set the extras parameter when you create the AliRtcEngine object. The following sample code provides an example to show how to set extras to set the resolution of a minor track to 320 × 180, the frame rate to 5 fps, and the bitrate to 140 Kbit/s:

{
  "user_specified_low_bitrate_stream_parameter": {
    "width": 320,
    "height": 180,
    "frameRate": 5,
    "bitRate": 140
  }
}

Note

When you set the resolution of a minor track, the valid values of the width are [64,640] and the valid values of the height are [64,480].
If you set the frame rate of a minor track to be greater than that of a major track, the frame rate of the minor track is adjusted to that of the major track. If you set the frame rate of a minor track to 0 or a negative number, the frame rate of the minor track is adjusted to 10.
If you set the bitrate of a minor track to be smaller than the minimum bitrate, the actual bitrate is the bitrate that you set. If you set the bitrate of a minor track to be larger than the maximum bitrate, the actual bitrate is the maximum bitrate.

For more information about the extras parameter, see extras parameters.

Customize major track specifications

To customize major track specifications, you can set the resolution, frame rate, and bitrate based on the following table and the actual bandwidth.

Resolution (width:height)	Frame rate (unit: fps)	Bitrate (unit: Kbit/s)
Resolution (width:height)	Frame rate (unit: fps)	Minimum value	Recommended value	Maximum value (multiple of the recommended value)
160 × 120	5	10	30	× 3
	10	20	55	× 3
	15	30	80	× 3
	20	40	100	× 3
	30	60	130	× 3
120 × 120	5	10	25	× 3
	10	17	50	× 3
	15	25	70	× 3
	20	34	90	× 3
	30	50	115	× 3
320 × 180	5	15	65	× 3
	10	30	110	× 3
	15	45	170	× 3
	20	60	220	× 3
	30	90	300	× 3
180 × 180	5	10	50	× 3
	10	17	70	× 3
	15	26	100	× 3
	20	34	130	× 3
	30	51	180	× 3
240 × 180	5	15	60	× 3
	10	30	90	× 3
	15	45	130	× 3
	20	60	165	× 3
	30	90	230	× 3
320 × 240	5	20	100	× 2
	10	40	170	× 2
	15	60	256	× 2
	20	80	320	× 2
	30	120	400	× 2
240 × 240	5	15	70	× 2
	10	30	100	× 2
	15	45	150	× 2
	20	60	200	× 2
	30	90	256	× 2
424 × 240	5	26	100	× 2
	10	53	170	× 2
	15	79	260	× 2
	20	105	340	× 2
	30	158	430	× 2
640 × 360	5	83	200	× 2
	10	165	340	× 2
	15	248	512	× 2
	20	330	600	× 2
	30	495	700	× 2
360 × 360	5	30	120	× 2
	10	60	180	× 2
	15	90	260	× 2
	20	120	330	× 2
	30	180	400	× 2
480 × 360	5	40	150	× 2
	10	80	240	× 2
	15	120	350	× 2
	20	160	430	× 2
	30	240	512	× 2
640 × 480	5	110	200	× 2
	10	220	350	× 2
	15	330	512	× 2
	20	440	600	× 2
	30	660	700	× 2
480 × 480	5	83	170	× 2
	10	165	260	× 2
	15	248	400	× 2
	20	330	470	× 2
	30	495	600	× 2
840 × 480	5	180	256	× 2
	10	360	512	× 2
	15	540	610	× 2
	20	720	800	× 2
	30	1080	930	× 2
1280 × 720	5	400	400	× 1.5
	10	800	800	× 1.5
	15	1200	1200	× 1.5
	20	1600	1600	× 1.5
	30	2400	2400	× 1.5
960 × 720	5	250	250	× 1.5
	10	500	500	× 1.5
	15	750	750	× 1.5
	20	1000	1000	× 1.5
	30	1500	1500	× 1.5
1920 × 1080	5	500	500	× 1.5
	10	1000	1000	× 1.5
	15	1500	1500	× 1.5
	20	2000	2000	× 1.5
	30	3000	3000	× 1.5
2560 × 1440	5	800	800	× 1.5
	10	1600	1600	× 1.5
	15	2400	2400	× 1.5
	20	3200	3200	× 1.5
	30	4800	4800	× 1.5
3840 × 2160	5	1000	1000	× 1.5
	10	2000	2000	× 1.5
	15	3000	3000	× 1.5
	20	4000	4000	× 1.5
	30	6000	6000	× 1.5

Note

The default resolution of a major track is 640 × 480, the default frame rate is 15 fps, and the default bitrate is 512 Kbit/s.
If the major track is a camera track, set the maximum resolution to 1920 × 1080 and the frame rate to 30 fps.
If the major track is a screen track, set the maximum resolution to 3840 × 2160 and the frame rate to 30 fps.
We recommend that you do not set the bitrate when you set the video specifications. RTC SDK sets an appropriate bitrate based on the resolution and frame rate of the video.