Dummy frames in AVI : overhead ?

[ChristianHJW]

Hi,

no this is NOT going to be an advertising thread for another container format. I assume its close to zero, but i'd like to know anyhow ( just nosey ).

The dummy frame itself has a value of 0, so i assume its 1 byte and it really shouldnt add anything, i guess the only extra overhead is due to the fact that the b-frame packed with the I/P frame into one single AVI chunk needs some additional bytes in the chunk so it can be separated/differentiated from the preceding frame ?

Can any XviD dev with indeep knowledge about the bitstream give me a rough figure, say based on an encoding with only 1 b-frame on a 200,000 frame movie and an estimated 10,000 b-frames in it ?

Thanks ...

[Koepi]

AVI frame overhead is 24 bytes.

If you have a "dropped frame" it takes 24 bytes as well.

Regards
Koepi

[ChristianHJW]

I didnt know about the 24 bytes for a frame in AVI, but thats not exactly what my question is about. I'd like to know, what is the overhead of an AVI with b-frames created with a VCM codec and dummy frames, and another AVI ( maybe encoded with mencoder on LInux ) without those.

Now, the overhead for dummy frame is 0 in any case, because this is where the frame would normally sit if it wasnt a dummy but a real frame ... so the only overhead we have to know is the extra bytes that are necessary to pack the b-frame into the same chunk with the preceding frame it is referencing to ..... any ideas how much this is ?

[temporance]

Originally posted by ChristianHJW
so the only overhead we have to know is the extra bytes that are necessary to pack the b-frame into the same chunk with the preceding frame it is referencing to ..... any ideas how much this is ? Zero bytes.

AVI video overhead is (from memory, correct me if I'm wrong): 12 bytes per frame between frames plus 16 bytes per frame in the idx1 chunk (if present).

So overhead in bits/second is
8*(12+16) * fps
= 224 * fps

Which corresponds to 5.4kbit/s at 24fps framerate, going up to 13.4kbit/s at 60fps. On the scale of things these are pretty small. Remember that we also waste nearly 1kbit/s just on the 00 00 01 b6 VOP header!!

[ChristianHJW]

12 + 16 bytes / frame = 28 bytes / frame

In my example movie with 200,000 total frames and 10,000 b-frames this equals

28 x 10,000 = 280,000 bytes = > 270 KB .... thats really almost neglectible i guess ....


And i guess there is no additonal overhead coming from the MPEG4ES frame headers also ?