[M4IF Technotes] Video Packet length and Profile-Level constraints

[Luca Celetto]

Table N.1 in MPEG-4 Visual standard lists the maximum size in bits for
Video Packets
Simple Profile @ Level 1 : 2048 bits
Simple Profile @ Level 2 : 4096 bits
Simple Profile @ Level 3 : 8192 bits
According to pen and paper computation (and some simulations), it is not
impossible that at least Level 1 constraint is overcome by a single
macroblock when QP is very low.  For instance, worst case when all DCT
coefficients are ESCAPEd
6:    blocks in macroblock
63:  AC coefficients
24:  bit for worse case ESCAPE sequence
total 9072 bits (without adding headers and DC coefficients!).
My conclusion is that it is compulsory to check each macroblock length
and eventually re-encode it with less bits. This seems to me a big waste
of computation, expecially if you have real-time constraints and you
need to ensure certain timings.
Any suggestion?