dumb Q: Are there VBR options for P2?
- Thread starter wplate
- Start date
Luis Caffesse
Admin
Not as it stands today.
But this is not because of some limitation of P2 technology - but because the DVCProHD codec is not an interframe codec,
so the same compression is applied to each frame across the board.
But this is not because of some limitation of P2 technology - but because the DVCProHD codec is not an interframe codec,
so the same compression is applied to each frame across the board.
Barry_Green
Moderator
Well, it depends on how you mean VBR. VBR is typically a GOP-based idea, meaning that the bitrate per group can vary as needed, as long as the average bitrate comes in about where needed (as opposed to CBR, which forces a fixed bitrate).
No format that records to P2 is GOP-based, so we will likely never see VBR in that context. DV, DVCPRO, DVCPRO50, and DVCPRO-HD are all CBR in that every frame is allocated a constant bandwidth. However, each individual frame is capable of reassigning its bit budget to blocks that need more bandwidth (which is one way that DV differs from JPG; JPG assigns a fixed bit budget to each macroblock, whereas each macroblock in DV is essentially VBR as needed). That's why "letterbox" mode looks slightly sharper than the same basic section of a full-frame 4:3 image -- the bits that would have been used for the black bars can be freed up and reassigned where they're needed, making the "letterbox" area less compressed.
No format that records to P2 is GOP-based, so we will likely never see VBR in that context. DV, DVCPRO, DVCPRO50, and DVCPRO-HD are all CBR in that every frame is allocated a constant bandwidth. However, each individual frame is capable of reassigning its bit budget to blocks that need more bandwidth (which is one way that DV differs from JPG; JPG assigns a fixed bit budget to each macroblock, whereas each macroblock in DV is essentially VBR as needed). That's why "letterbox" mode looks slightly sharper than the same basic section of a full-frame 4:3 image -- the bits that would have been used for the black bars can be freed up and reassigned where they're needed, making the "letterbox" area less compressed.