Don't Forget H.261 (Q94)

The information in this article applies to:

A video-capable H.323 terminal is required to encode and decode H.261 video. It may optionally encode and decode H.263 video. Some vendors have chosen to do H.263 and not H.261, presenting basic interoperability problems. Section 6.2.4/H.323v2: "All H.323 terminals providing video communications shall be capable of encoding and decoding video according to H.261 QCIF. Optionally, a terminal may also be capable of encoding and decoding video according to the other modes of H.261 or H.263." In summary,

• An H.323 terminal must at least encode and decode H.261 QCIF.
• If it supports H.263, it must encode and decode QCIF.
• If it supports H.263 at CIF or higher resolution, it must also support H.261 at CIF resolution.