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Posted by Smarty on 10/05/54 11:38
A codec is also used in transcoding the incoming HDV content into 'proxy' /
intermediate formats such as Apple's Intermediate Codec or Cineform's
Connect HD (such as found in Vegas 6.0).
Smarty
"Frank" <frank@nojunkmail.humanvalues.net> wrote in message
news:ed0mt1lmmbls31cmnejgrauvr5gl2nm413@4ax.com...
> On Fri, 27 Jan 2006 16:30:16 GMT, in 'rec.video.production',
> in article <Re: HDV capture on under-powered PC>,
> "Nappy" <noemail@all.com> wrote:
>
>>
>>"Smarty" <nobody@nobody.com> wrote in message
>>news:pLWdnZaFneCCxUTenZ2dnUVZ_v-dnZ2d@adelphia.com...
>>> Chris,
>>>
>>> I'm really not so sure the disk is indeed the bottleneck.
>>>
>>> Since normal DV capture has exactly the same data rate as HDV, and is
>>> captured correctly by Paul's system, I am much more suspicious of the
>>> CPU
>>> and / or perhaps the bus speed of his PC.
>>>
>>> The codec has a lot more work to do in encoding the incoming HDV stream,
>>and
>>> this is where the CPU and bus are probably the issue.
>>
>>
>>It is a 25Mb data stream.
>
> Yes, 25 Mbps in the case of 1080i HDV. 720p HDV is 19.7 Mbps, however.
>
>>The codec doesn't do much on the data's way into
>>the hard disk. It certainly does NO encoding. Decoding the stream for
>>display is where the extra clock cycles go..
>
> This depends upon the specific capture software being used.
>
> Some programs write the raw HDV MPEG-2 Transport Stream to disk as an
> .m2t file. In this case, since the input data is unchanged, a codec is
> not involved in the process.
>
> Others change the HDV MPEG-2 Transport Stream into an MPEG-2 Program
> Stream and write the data to disk as an .mpg file. No codec is
> involved here either since the datastream is unchanged.
>
> Others decompress the (long-GOP) HDV MPEG-2 Transport Stream into an
> I-frame-only MPEG-2 Program Stream and write an .mpg file to disk.
> Here, obviously, a codec is involved, although all that it's doing is
> a normal MPEG-2 decoding operation. No quality loss is involved.
>
> And finally, other capture programs transcode the incoming MPEG-2
> Transport Stream to an .avi file using a proprietary visually lossless
> codec (the degree of visual losslessness is, of course, in the eye of
> the beholder). In this case, and as in all audio or video transcoding
> operations, two codecs are involved, one to decode the incoming MPEG-2
> data and another to perform the encoding function. Some small degree
> of quality loss will result from this transcoding operation, but many
> people find it to be unnoticeable and therefore quite acceptable for
> their purposes, especially given that the resultant intraframe-encoded
> file is much easier to edit than the original intraframe-encoded
> long-GOP MPEG-2 HDV data.
>
> It should be noted that most programs that change the incoming HDV
> MPEG-2 Transport Stream into another format before saving the data to
> disk also usually decompress the incoming lossy compressed HDV MPEG-1
> Layer II audio stream and save it in an uncompressed LPCM (linear
> pulse code modulation) form. Again, this is done to facilitate
> editing.
>
> --
> Frank, Independent Consultant, New York, NY
> [Please remove 'nojunkmail.' from address to reply via e-mail.]
> Read Frank's thoughts on HDV at http://www.humanvalues.net/hdv/
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