[opendtv] Re: New DVDs already sparking copy-protection confusion
- From: Gary Hughes <ghughesml@xxxxxxxxxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Wed, 01 Mar 2006 12:41:36 -0500
At 04:04 PM 2/28/2006 -0800, Kilroy Hughes wrote:
>[KH] Progressive encoding is illegal on DVD-Videos.
That is not quite correct
>Progressive_sequence=3D0 is required, and only 30Hz or 25Hz frame rates
>allowed.
Progressive_sequence=0 does not prohibit progressive encoding. It only
says that interlaced encoding is permitted, but not required. The picture
coding extension specifies how each picture is encoded. In the 30Hz
world, a correctly inverse telecined 24P source results in a sequence of
progressive encoded frames, along with the repeating pattern of
repeat_first_field
and top_field_first flags (also in the PCE). The sequence header will indicate
a frame rate of 29.97, but each second of bitstream will contain 24 progressive
encoded frames. I think this meets the definition of "progressive encoding".
>There has been a long battle to change production practices
>and tools to support consistent and invertible telecine so 24P could be
>tunneled through 30i transport streams. Accurate 24P cadence in 30i
>syntax was the exception for most movies for the first few years of DVD,
>but is now the rule.
In my previous employment I designed the trick mode handling for a VOD server
that makes use of the I frames as they exist in the original stream (to avoid
the need for trick mode files). Film content that has not been through IVTC
can exhibit terrible interlace flicker as you might imagine and I spent much
of last year dealing with these issues.
Various people maintained that non-video data, such as closed captioning, could
not be accommodated in IVTC content which is of course bogus. Regrettably one of
the major content providers made a decision to not use IVTC in any of their
content, largely because some of their production tools did not handle the
stream timestamps correctly in IVTC content (if you repeat a field, that has to
be reflected in the PTS and DTS values). In the end I designed a new trick
mode sequence that forces the set top decoder to deinterlace by making both
fields reference the same original field when in pause etc when playing out
such content.
>BD format now allows 24P encoded Transport Streams. HD format doesn't,
>but it identifies 24P encoded as 30i to allow accurate decoding to 24P.
Which brings us back to the discussion in DVDlist :-)
If I understand correctly (all numbers modulo 1000/1001 as needed)
BD allows 24P content to be encoded at 24 progressive frame/sec with the
sequence header frame rate set to 24 and no use of the 3:2 pulldown flags,
so the decoder could drive the display at 24 frame/sec.
HD DVD requires 24P content to be encoded as 24 progressive frames/sec with
the sequence header frame rate set to 30 and the picture coding extension
containing the necessary flags to reconstruct the 3:2 pull down, and presumably
drives the display at 30 frame/sec.
Some questions...
Can a BD player can also perform the 3:2 pull down on its output if needed?
Does the BD format also allow for the 24 frames plus rff/tff IVTC approach,
or was that the gist of your original comment in DVDlist?
Sorry if this seems overly pedantic. MPEG does that to people (this is your
brain, this is your brain on MPEG)
gary
Gary Hughes (ghughes@xxxxxxxxxxxxxxxxxx)
Stargate Video Systems
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