FFmpeg: Lossless video conversion from AVI to MP4 possible for ALL codecs ?

[pxstein]

I consider to convert some dozens of old AVI video files from AVI to MP4 container by using ffmpeg with the following simple command:

ffmpeg.exe -i oldvideo.avi -vcodec copy -acodec copy newvideo.mp4

I place strong emphasis to the fact that the conversion is lossless. No re-encoding should take place.

Does this really work for all kind of videos and codecs?

Even for those which are originally encoded with Divx or Xvid?

With or without constant bitrate?

Are the existing keyframes accessible as before?

Are timestamps and other existing tags (in header) kept?

Sometimes I read about some necessary additional parameters like "-map 0".
When are they required?

Thank you
Peter

[LigH.de]

No. The MP4 container standard only specifies a limited number of video formats which are supported in this container. These are mainly the MPEG video codec family.

DivX and Xvid are implementations of MPEG-4 (Advanced) Simple Profile, they are supported.

Video bitrate is hardly ever "constant" in efficiently compressing video formats. Their purpose is to use "as much as required to approach a limit".

If a source video format in an AVI container is supported, then remultiplexing it into an MP4 container should generally be bit-exact. Even timestamps may be kept; this is often a problem when people try to concatenate videos and the timestamps are not continuous at the connection. For such a case, ffmpeg is able to regenerate continuous timestamps during a concatenation.