[Libav-user] ffmpeg default for -b:v ?

["René J.V. Bertin"]

Hello list,

A couple of questions about the way ffmpeg handles bit rates while converting:
I'm using ffmpeg to convert a raw m4v file into a .mov container. The input file does not have any information about its frequency, size or bitrate in the header, so everything comes from the individual packets (frames). When I repackage (-vcodec copy), I obtain a .mov at 12Hz, with a bitrate of approximately 4000kb/s.

Questions:
- when encoding, say to mjpeg, what is the bitrate chosen by ffmpeg when one doesn't specify a rate explicitely?
- to obtain a .mov with approximately 4000kb/s, I need to add -b:v 1000k under Mac OS X, but -b:v 2000kb/s on win32 ... why this difference (and why don't I get a rate closer to the requested rate)?

Thanks in advance,
René