Re: [Avid-L2] All H.264 decodes created equal?

Wow. Dylan, thanks for doing all the tests! What a public service!

What tool did you use to measure the SSIM of the images?

Again, thanks for posting your results, awesome work.

best-
-Nat

On Jun 15, 2010, at 6:50 AM, Dylan Reeve wrote:

> I got curious about this and went and tested the transcodes...
>
> Basically DNxHD 120, 185 and 185X were effectively identical to the source
> clip. DNxHD 36 was very very good also, I couldn't see any differences
> visually, and those I could detect were minimal. I also tested XDCAM EX
> (35Mb/s) and XDCAM HD422 (50Mb/s) with strong results, again both appeared
> visually identical in my tests.
>
> It seems that the detail retained in the H.264 is easily simple enough to be
> effectively compressed into other codecs with minimal variance or loss,
> especially where those codecs are of significantly higher baseline quality.
>
> I blogged it -
> http://dylanreeve.com/videotv/avid/2010/transcoding-canon-dslr-footage.html
>
> On Tue, Jun 15, 2010 at 7:38 PM, Dylan Reeve <dylan@dylanreeve.com> wrote:
>
>> In theory there should be no quality differences in decode methods. The
>> only real differences should be in terms of decode time - I'm not sure how
>> each of the applications do it, but I'd assume Adobe's apps are doing it a
>> little differently as I believe their Mercury engine improves the decode
>> times, using the power of the GPU.
>>
>> Canon's DSLR files confuse me, they are a pretty high bitrate (around
>> 46Mb/s) but deliver pretty poor performance for that amount of data. They
>> are 8bit and 4:2:0 sampled and tend to exhibit pretty noticable quantization
>> artifacts. I'd tend to assume that any of the "full" DNxHD codec are more
>> than capable of fully representing all the recorded image data (120, 185 or
>> 220).
>>
>> I'm fairly certain, however, that H.264 at such high bitrates should be
>> able to do a lot better. If MPEG2 can deliver the quality it does with
>> 50Mbit/s in XDCAM HD422, then H.264 at almost the same bitrate can surely be
>> better?
>>
>>
>> On Tue, Jun 15, 2010 at 4:13 PM, nat jencks <natjencks.lists@gmail.com>wrote:
>>
>>>
>>>
>>> In the course of researching various methods for processing 5Dmk2 and 7D
>>> footage as dailies I have hit two questions for the lists collective wisdom.
>>>
>>> 1) Is there any difference between the various tools (Mpeg Streamclip, FCP
>>> log and transfer, Magic Bullet Grinder, Adobe CS5, Neo Scene, etc) on the
>>> DECODE side of things?
>>>
>>> From the research that I have done, all of these tools use the underlying
>>> quicktime framework to decode the H.264, and any differences in transcoding
>>> are the result of different types of encoding.
>>> Possible exceptions are Neo Scene, and CS5, but even these may use the
>>> same quicktime framework to decode?
>>>
>>> 2) On the ENCODE side of things, what is people's real world experience
>>> regarding what type of datarate you need to go with to get ALL the
>>> information out of these source files...
>>> Prores HQ? Prores444? Uncompressed DPX? Obviously the safe thing to do is
>>> go for an offline/online workflow with ProresLT for offline and Uncompressed
>>> DPX for online, but if ProresHQ would capture all the source data without
>>> introducing compression artifacts it would be nice to avoid offline/online
>>> scenarios.
>>>
>>> Thanks in advance!
>>>
>>> Best-
>>> -Nat
>>>
>>> [Non-text portions of this message have been removed]
>>>
>>>
>>>
>>
>>
>>
>> --
>> Dylan Reeve
>> http://dylanreeve.com/
>>
>
>
>
> --
> Dylan Reeve
> http://dylanreeve.com/
>
>
> [Non-text portions of this message have been removed]
>
>
>
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