[mythtv-users] Re: Re: Best video capture resolution for output to TV?

[Bruce Markey]

Allen T. Gilliland IV wrote:
>>Good point (if I undersood you correctly =). The bit
>>rate
>>also has an impact on how much detail is preserved
>>during
>>compression. In testing I found that given a medium
>>res and
>>medium bit rate, raising the bitrate improved the
>>picture
>>quality more than raising the resolution to hit a
>>target
>>file size.
> 
> 
> Actually, the bitrate is exactly what controls the
> quality of your recording.  Basically, uncompressed
> video = video at max bitrate.  Essentially, when you
> compress your videos you can think of it in terms of
> compressing each frame individually.  The bitrate
> controls how much data or storage space you are
> willing to commit to a single second of video.  So if
> your bitrate is 3000 kbit/s @ 30 fps, then you are
> using 100 kbits per frame.

It sounds like what you are describing is M-JPEG. For MPEG2
and MPEG4 they encode the differences from one frame to
the next. Therefore, the bitrate can be a small fraction of
the actual data in a frame. If there is very little motion
a low bit rate usually gives you a frame pretty close to
the original. However, if there is a lot of motion and the
differences are greater then can be fit into the bitrate,
the changes are simplified which causes artifacts. For a
given target file size, if there is a lot of motion, lower
res and higher scaled  bitrate will look better. With little
motion, higher res and lower scaled bitrate will look better.
The myth default of 2200 is pretty low so I think most 
people will see a bigger improvement by raising the bitrate
than by raising the resolution.

--  bjm