[mythtv-users] Suggested bitrate for transcoding HD Mpeg 2 to Mpeg 4

[Richard Morton]

Hi,

I am not sure what you are asking... MPEG4 is commonly referred to but
is in fact a suite of codecs including at least 2 video codecs an
audio codec and a container format.

If you are talking about MPEG4 part 10; otherwise known as H.264 then
it is much preferable to allow the codec to try and determine what
bitrate should be used based on a quality variant that you specify;
somewhere between 16 and 20 is typical.

If you are referring to MPEG4 part 2; a.k.a. DIVX/XVID then I dont use
this codec.

I tend to use an mkv container rather than the mpeg4 container and
pass the audio through as broadcast may contain multiple streams and
is already compressed to hell with MP2 or MP3 so, transcoding it isn't
a great idea although there may be some small incremental gains
transcoding to MPEG4 AAC (advanced audio codec, a.k.a mp4a/m4a) as
long as you dont mind the reduced quality.

Now my comments about transcoding audio is also true of video,
although on small screens (30" maybe even 40") any change is likely to
not be noticeable and the gains of going from mpeg2 to mpeg4part10 is
very large in disk space (typically half the disk space on 1gb/hour
with mpeg2) but going from mp3 to m4a is only going to save an
additional 100mb; although the codeing time for audio is substantially
quicker of course.