Use a bitstream analyzer like h263_parse (from libavutil) or the Elecard StreamEye (trial). A superior sample will use at least:
: Offers classic video test sequences often used in academic research, including the well-known "Foreman" and "Salesman" clips in .vsl format. Access them at the H.263 Video Codec Project Tdarr Sample Library h 263 video sample download better
Use FFmpeg’s libavcodec H.263 encoder (which supports most Annexes) to create your own better sample. Use a bitstream analyzer like h263_parse (from libavutil)