On Wed, 20 Nov 2024, martin schitter wrote:
On 19.11.24 22:47, Marton Balint wrote:
The current parser does things which a parser should not, like skipping
parts
of the packet header, but it does not actually able to packetize a raw
DNXUC
bitstream.
You're right! I simply can't reject this judgment about the obvious flaws of
the current implementation.
Although I see significant improvements in your rewrite attempt, I'm still
unsure, if it really solves the main issue.
Your design makes a lot of sense, if someone wants to copy the DNxUC video
stream without any additional de-/encoding by just passing through this kind
of unprocessed 'pack'-box data. That's a very efficient kind of handling for
some cases.
But I'm still not completely satisfied by this solution, because I'm
skeptical, that it builds a suitable solution for multi-component cases (RGB
+ alpha or multiple FX/rendering layers) as well. And that's IMHO the much
more puzzling open problem.
The layering issue is for the decoder to take care of, not the parser. The
parser's primary job is to packetize a non-packetized stream and maybe get
some basic information about the packets which normally the container has.
This patch fixing the parser should not be contriversal, because it only
changes how the parser behaves, there is no argument about that as far as
I know.
This kind of layered content should be perhaps split immediately within the
MXF demuxer and generate multiple video streams very early. But unfortunately
this doesn't quite fit into the current MFX demuxer design. Otherwise, we
will have to divide the video stream at a later stage, where such changes are
usually not expected anymore.
How do you think about this difficulty?
I personally still don't have any convincing solution for this quest.
Some cases the decoder can support, maybe some cases it can't. Let's focus
on the ones which it can. E.g. planar formats can be used for multiple
icmp boxes.
Rework the parser logic to work similar to other parsers and be able to
correctly packetize raw DNXUC bitstreams.
In principle, I appreciate your rewrite. It's definitely an improvement, and
it's perfectly acceptable to shift all further packet processing into the
decoder module.
Honestly I'm rather surprised, that someone still wants to improve this DNxUC
related code, because I'm personally more in the mood to ask for reverting
the already merged parts. I simply don't want to waste my time on useless
fights...
I get it, reaching a consensus is not always possible and the debate can
be demoralizing. But that is how it is, if you want to contribute to open
source, you have to accept that. Some patches may get rejected today,
maybe they will get accepted in a year with no fuss. It happens.
Regarding DNXUC and the MXF demuxer the main question is not even about
the DNXUC decoder, but the MXF demuxer, if it should output RAWVIDEO codec
(where possible) or always DNXUC codec. Deciding on this should not delay
the inclusion of the DNXUC decoder the way I see it. And in my opinion the
DNXUC decoder should support everything the format supports regardless of
what the MXF demuxer does. (A library user might use his own demuxer and
only the DNXUC decoder from ffmpeg).
Regards,
Marton
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