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Adjusting audio and video — Linux

You can make audio and video adjustments to published and subscribed streams:

Publishing audio or video only

You can toggle audio and video on or off, by calling the otc_publisher_set_publish_audio() and otc_publisher_set_publish_video() functions, passing in `OTC_FALSE` or `OTC_FALSE` as the `publish_audio` and `publish_audio` parameters. For example, the following code turns audio off:

otc_publisher_set_publish_audio(publisher, OTC_FALSE);

Publishing in a voice-only session

To set up a voice-only session, instantiate an otc_publisher_settings struct, call the otc_publisher_settings_set_video_track() function, passing in OTC_FALSE as the enabled parameter. Then use the otc_publisher_new_with_settings() function to create. For example, the following code creates a publisher for a voice-only session:

otc_publisher_settings publisher_settings = otc_publisher_settings_new();
otc_publisher_settings_set_video_track(publisher_settings, OTC_FALSE);
otc_publisher_callbacks publisher_callbacks = {0};
// Set callbacks for the publisher. Then:
otc_publisher publisher = otc_publisher_new_with_settings(publisher_callbacks, publisher_settings);

Using a custom video capturer

The otc_publisher_new() function includes a capturer parameter. If you set this to NULL, the SDK uses the default system camera as the source for the published video stream. However, you can use a custom video capturer for the publisher by defining a otc_video_capturer_callbacks struct and passing it in as the capturer parameter of the otc_publisher_new() function. The otc_video_capturer_callbacks struct includes function pointers to callback functions that are invoked upon events related to the publisher video, such as when the video capturer needs a new video frame.

To see an example, see the Custom Video Capturer sample of the opentok-linux-sdk-samples repo.

Mirroring the local display of a publisher's video

By default, the local renderer for published video mirrors the video. You can set the mirror_on_local_render property of the otc_video_capturer_settings instance obtained by calling the get_capture_settings(capturer, settings) function. Set it to true to have the video mirrored in the local renderer of the publisher. Set it to false to have it not be mirrored.

This setting only affects the rendered video in the publisher's client application. It has no effect on the video in subscribing clients.

Using a custom audio driver

You can define a custom audio device, to supply audio to all publishers in the client and to handle the mixed audio stream from all streams the client subscribes to.

A custom audio device is represented by an otc_audio_device struct. And an otc_audio_device_callbacks struct includes function pointers to functions that act as the audio-related callbacks that the OpenTok Linux SDK invokes.

To see an example, see the Custom Audio Device sample in the opentok-linux-sdk-samples repo.

Setting the audio volume for a subscriber

You can individually set the audio volume for each subscriber by calling the otc_subscriber_set_audio_volume() function.

Subscribing to audio or video only

By default, a subscriber is initialized to subscribe to audio and video, if they are available. You can toggle audio on or off by calling the otc_subscriber_set_subscribe_to_audio(otc_subscriber *subscriber, otc_bool subscribe_to_audio) :

// audio off:
otc_subscriber_set_subscribe_to_video(subscriber, OTC_FALSE);
// audio on:
otc_subscriber_set_subscribe_to_video(subscriber, OTC_TRUE);

You can toggle video on or off by calling the otc_subscriber_set_subscribe_to_video(otc_subscriber *subscriber, otc_bool subscribe_to_video) :

// video off:
otc_subscriber_set_subscribe_to_video(subscriber, OTC_FALSE);
// video on:
otc_subscriber_set_subscribe_to_video(subscriber, OTC_TRUE);

Detecting whether a stream has audio or video

You can call the otc_stream_has_audio() and otc_stream_has_audio() member functions of an otc_stream instance to see if it has audio or video.