Search code examples
h.264

The maximum size with bytes of one NAL unit

I can't find any clue in H.264 spec, anybody can give a clear and simple maximum size regardless of its profile and level?

I'd like to parse H.264 stream, and copy one complete NAL unit buffer to a fixed-size buffer which can hold all bytes of one NAL unit.

Thanks.

Solution

  • AVC level 6.2 allows up to 139264 macro blocks per frame. If we use 10 bit color 4:4:4 it’s 30 bits per pixel. So (30*139264*16*16)/8 gives about 133.7mbytes for an uncompressed image. H.264 has a PCM_I encoding that allows for uncompressed images. There is a little ovehead for the NAL header, so let’s call it 134Mbyte. But in the real world the frame probablly will not be this large, and will likely be compressed.