On 25/01/2011 03:42 PM, Warp wrote:
> Invisible<voi### [at] devnull>  wrote:
>> Spec claims it comes with a 4 GB flash card, but that's going to fill in
>> seconds I would imagine.
>
>    A 4GB DVD can contain at least an hour of decent-quality video. And that's
> just using MPEG-2. (Granted, HD video has a higher resolution, but with MPEG
> the bitrate does not scale linearly with the resolution.)

So how come BluRay disks are 5x the storage capacity, yet still have 
roughly the same run time? I thought it was because HD video requires 
more space to store.

>> I was under the impression that the compression algorithm remains the
>> same regardless of what bitrate you select.
>
>    MPEG-4 is a bit more complicated than that. It's not like it's JPEG.

I thought it was more or less the case that *all* codecs work by 
transforming the input, deciding how "important" each signal component 
is, and then keeping only the most important bits, according to what the 
requested bitrate was. I don't see anything there that makes a higher or 
lower bitrate change the amount of compute power required.

(Well, OK, maybe I do. I know a some codecs do a DCT, quantise it, and 
then entropy-encode the results. Bigger results = more stuff to encode.)

Post a reply to this message