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Cisco TelePresence MCU 4500 Series

Differences between the content modes on the MCU

What are the differences between the content modes on the MCU?

This article applies to the following products, running version 4.3 (or later) of the MCU software:

  • Cisco TelePresence MCU 4200 Series
  • Cisco TelePresence MCU 4500 Series
  • Cisco TelePresence MCU 5300 Series
  • Cisco TelePresence MCU MSE Series

Transcoded, Passthrough, and Hybrid content modes

Content is an extra video channel provided by a single conference participant that is intended to be seen by all participants, for example, slides in a presentation. The content channel appears the same for all participants and cannot be individually customized (for example, layout).

The MCU has two main modes to carry content from source to destination: Passthrough or Transcoded. There is also a third mode which is a combination of Passthrough and Transcoded mode. It is called Hybrid mode.

Each mode is available on a per-conference basis and you can select the mode on the configuration page for the conference.

Transcoded mode

In Transcoded mode, the MCU always decodes the incoming content stream and re-encodes it, using the preferred outgoing Transcoded codec, before sending the content to all endpoints. The key points of this mode are:

  • More endpoints can receive content because the MCU can adapt the format to the capabilitites of the endpoints. However, the trade-off is that all endpoints receive content encoded for the least capable endpoint in the conference, which may not be an ideal experience for more capable participants.
  • Endpoints not capable of receiving content, will receive content in main video if 'Display content in normal video channel' option is enabled.
  • A thumbnail of content is viewable from the web interface.
  • Transcoded mode was the only content mode available in MCU applications prior to MCU software version 4.3.
  • A video port or a dedicated content port is required to support Transcoded content.

Passthrough mode

In Passthrough mode content is not decoded and is simply repackaged and sent to each eligible endpoint in the conference. The key points of this mode are:

  • In this mode, the incoming content stream is passed through to participants who are able to support the same codec as the original content stream.
  • Endpoints that are not capable of receiving Passthrough content will not receive content.
  • Passthrough mode is most suitable when the endpoint environment is homogenous, and participants expect the best quality that the endpoints can deliver.
  • No video decoder or encoder will be allocated on MCU for content channel.
  • Content is delivered with minimum latency since MCU does not decode incoming stream.
  • A thumbnail of content is not viewable from the web interface.
  • No extra video port is used for Passthrough mode.

Hybrid mode

Hybrid mode is a combination of Transcoded and Passthrough mode. It decodes and re-encodes the content stream as in Transcoded mode to support endpoints that cannot decode the Passthrough content. Repackaged original content as in Passthrough mode is sent to endpoints that advertise support for it. The key points of this mode are:

  • Some endpoints might get better quality content via Passthrough, where Transcoded mode might have sent lower content quality.
  • More endpoints can receive optimized content because the MCU can adapt to the capabilities of the participants.
  • Endpoints not capable of receiving content, will receive content in main video if 'Display content in normal video channel' option is enabled.
  • A thumbnail of content is viewable from the web interface.
  • This mode is suitable for an environment which has a mixture of endpoints that support different codecs for content.
  • A video port or a dedicated content port is required to support Hybrid content.

March 1st, 2013 TAA_KB_699