AC3 Muxing overhead

[X-Nemesis]

The AC3 file I have for FOTR is 401mb's...does that mean when I mux the file with my avi that the avi file will be exactly 401 mb's larger?

[iago]

No. There will be a muxing overhead, which you can calculate using GKnot, or a bitrate calculator, etc.

[alexnoe]

Since the muxing options have influence on the actual overhead, any program which claims to precisely calculate the overhead without knowing the settings is claiming to do something impossible.

The overhead calculation is not at all easy!

Each chunk causes an overhead of:
- 24 bytes for standard avi
- 16 bytes for open-dml without legacy index / open-dml beyond 1 GB
- 32 bytes for open-dml with legacy index within the first GB

Nbr of Chunks is: Nbr of video frames + Nbr of audio chunks,

with:
- MP3-VBR: one chunk each 24 ms
- AC3 (with avi-mux gui 1.11): one chunk each 64 ms
- DTS (with avi-mux gui 1.11): one chunk each 21 ms
- others: depending on interleave setting

If you use AVI-Mux GUI with rec-lists and a small audio interleave, then the overhead caused by each rec list structure will also be noticeable (each rec list causes 28 bytes for standard avi / open-dml+legacy index within the 1st GB, and 12 bytes for open-dml without legacy-indec / open-dml beyond 1 GB).

For the standard setting of 75, the overhead caused by rec lists will not be noticeable.