PTSs: Presentation times size: 32 or 33 bits.

[jsoto]

AFAIK, the Presentation times in Navs are always 32 bits wide, but the PTSs in the PES header are 33 bits wide.

I know a value of 32 bits, used as unsigned, gives you more than 12 hours of playing time, but I'm curious about the reason of the difference in the PTS sizes..

jsoto

[neuron2]

NAVs are on DVDs where the program is never longer than 14+ hours, so the 33rd bit is not required. In practice though, even with set-top boxes, the 33rd bit can be ignored, because the decoder already allows for wraparound and discontinuities because they are encountered on channel changes.

[bigotti5]

Imho PTS/DTS is defined in MPEG and should be able to span 24 hours (maybe for broadcasting), PTM is defined for DVD-Video, no need to use more than 4 bytes (~13h).

[jsoto]

Thanks for your comments guys.

One last question about the ones inserted in the PTS coding. I suposse they are to avoid the start codes simulation. Am I wrong?

jsoto

[mpucoder]

Although pts/dts in pes headers is 33 bits, it is restricted to 32 bits for DVD use. Having bit 32 set is a violation of DVD spec. see Philips Verifier error 3210.

Those bits are called marker bits, and that is their purpose.

[neuron2]

One last question about the ones inserted in the PTS coding. I suposse they are to avoid the start codes simulation. Am I wrong? Avoidance of start code emulation is a design factor for the video elementary layer, not the program or transport layer.