Τάκη κολλάς χωρίς λόγο,έγραψα:
"Την μετατροπή σε 50hz ή 60hz που είναι απαραίτητη για την πλειονότητα των μέσων προβολής θα την κάνει το player κατα την αναπαραγωγή.Οπως και την κωδικοποίηση σε SD-pal για την σύνδεση και με συμβατικά μέσα προβολής."
"Το HD για να προβληθεί σε συμβατικές οθόνες θα μετατρέπεται σε pal/ntsc."
"Η εικόνα θα γίνεται pal ή ntsc με έναν pal encoder όπως το tv-out της κάρτας γραφικών μας"
"Δηλαδη που είναι το λάθος να πείς οτι το σήμα γίνεται pal όταν πάρεις το 1080p 24fps με colorspace HD και το κάνεις 720x576 με colorspace του pal?Τι το κάνεις?Αυτό δεν λέγεται pal?
Αυτό θα είναι αναγκαίο για συμβατικές συσκευές που δεν καταλαβαίνουν τίποτα άλλο πέρα απο pal."
"Οι κλασσικές αναλογικές έξοδοι (composite,svideo κ.λ.π.) θα πρέπει να είναι pal."
Οπως καταλαβαίνεις δεν μιλάω για "αν κανουμε downconvert ενα HD υλικο στην αναλυση του non-HD προβολικου μας τοτε αυτο γινεται αυτοματως PAL ή NTSC".
Αλλά για τις απλές αναλογικές εξόδους,οι οποιές πρέπει οπωσδήποτε να έχουν το colorspace του pal/ntsc
Ως προς το pulldown δεν το έπιασες σωστά:
a) Film material on NTSC DVD is usually encoded progressively at 23.976 frame/s, with special flags inserted into the MPEG-2 video stream that instruct the DVD player to repeat certain fields so as to accomplish 2-3 pulldown during playback
b) So what the best players do is use a standard MPEG-2 decoder to generate digital interlaced video and then feed that video to a deinterlacing chip
Αυτό που πάντα παίρνεις είναι το πεπλεγμένο pal/ntsc σήμα.Το οποίο γίνεται προοδευτικό.Γι`αυτό οι προβολείς μας αναφέρουν 60/50hz.Εχουν μετατραπεί τα 60/50 FieldsPS σε 60/50FramesPS.
επίσης
How The Information is Stored on Disc
"Itʼs important to understand at the outset that DVDs are designed for interlaced displays. Thereʼs a persistent myth that DVDs are inherently progressive, and all a DVD player needs to do to display a progressive signal is to grab the progressive frames off the disc and show them. This is not exactly true. First of all, a significant amount of DVD content was never progressive to begin with. Anything shot with a typical video camera, which includes many concerts, most supplementary documentaries, and many TV shows, is inherently interlaced. (Some consumer digital video cameras can shoot in progressive mode, and a handful of TV programs are shot in progressive, particularly sports events.) By comparison, content that was originally shot on film, or with a progressive TV camera, or created in a computer, is progressive from the get-go. But even for such content, there is no requirement that it be stored on the DVD progressively.
DVDs are based on MPEG-2 encoding, which allows for either progressive or interlaced sequences. However, very few discs use progressive sequences, because the players are specifically designed for interlaced output. Interestingly, while the sequences (i.e., the films and videos) are seldom stored progressive, there's nothing wrong with using individual progressive frames in an interlaced sequence. This may sound like a semantic distinction, but itʼs not. If the sequence is progressive, then all sorts of rules kick into place which ensure that the material stays progressive from start to finish. Whereas if the sequence is interlaced, then there are fewer rules and no requirement to use progressive frames. The encoder can mix and match interlaced fields and progressive frames as long as each second of MPEG-2 data contains 60 fields, no more, no less (or 50 fields per second for PAL discs). The progressive frames, when they are used, are purely for compression efficiency, but the video is still interlaced as far as the MPEG decoder is concerned.
The input to a DVD encoder (the instrumentation that is used to author a DVD) is almost always an interlaced digital master tape, even if the original material was shot on film. The video transfer is typically done at a different facility, and the output of the transfer is interlaced. Since the DVD encoding software doesn't even have access to a progressive master, it must rely on the same kinds of algorithms that a deinterlacer uses to put the proper fields together. Since there is essentially no requirement that it actually always put the proper fields together, other than compression efficiency, many encoders are conservative about using progressive frames. If the encoder cannot be sure that a frame is progressive, it will typically mark it interlaced, because the only real loss is a few bits of disc space.
When the mastering engineers view the disc for quality control, they view it on an interlaced monitor. They don't necessarily care how well it deinterlaces, because that's not part of the DVD spec. Some mastering houses do pay attention to the flags produced by their encoder, and some do view the disc on progressive players just for quality control, but that's not at all required.
In short, the content on a DVD is interlaced conceptually, and is stored in interlaced sequences. Frames can be marked "progressive" to help compression, but are not always marked that way, even when it would be correct to do so. In interlaced sequences, the encoder can either keep the fields separate, or combine them together into one frame, whichever is best for compression purposes. There is a flag on each image stored in the MPEG-2 stream called “picture_structure” that can be either “frame” for a full 720x480 pixel frame, or “top field” or “bottom field” for a single 720x240 field. (Weʼll learn about top and bottom fields later.) And it is allowed, but again not required, to set a flag called “progressive_frame” as a hint to the decoder that the fields in that frame were taken from the same frame of film. This allows for better pause and slow motion modes, and better down-conversion of 16x9 images for 4x3 displays. But this is again, purely optional. The content will play fine whether the data is structured as fields or frames, and whether the flag is present or not.
In fact, the encoder is allowed to combine fields that are not from the same film frame together, as often that produces better compression, even for inherently interlaced video. In such cases, the encoder is not supposed to set the progressive_frame flag, but again, if it does happen to get set, it will make no difference for normal playback on an interlaced display. And since interlaced displays are the only thing DVD was designed for, sloppiness with flags is more common than youʼd think.
The flags on the disc, and the structure of the frames, are purely hints. Interlaced video can be stored on the disc as frames, and progressive frames can be broken into fields. The progressive_frame flag can be there or not. It doesnʼt make any difference for interlaced playback. As we will see, though, it can make a big difference for progressive playback."
και
"There are two extra flags available in MPEG-2 to make it easier to create a disc that has 3-2 pulldown. These two flags are called “repeat_first_field” and “top_field_first.” A frame in the MPEG stream can have “repeat_first_field” set to “true,” and that tells the decoder to generate 3 fields from this frame, rather than 2. The decoder plays the first field, then the second field, then the first field again, thereby making the 3-field section of the 3-2 pulldown cadence. The next frame would generally have “repeat_first_field” set to “false,” so the decoder will generate 2 fields. Because fields have to alternate between even (bottom) and odd (top), the “top_field_first” flag tells the encoder which of the two fields in the frame should be sent out first. The “top” field is the odd numbered scan lines: 1, 3, 5…, while the “bottom” field is the even numbered scan lines: 2, 4, 6… If the top field is first on a 3-field frame, the decoder will output top, bottom, top. The next field needs to be a bottom field, so the next frame will have top_field_first set to “false."
Το pulldown έχει γίνει(οριστεί),απλώς αντι να αποθηκευτούν τα διπλά καρέ στο dvd το mpeg video έχει οδηγίες (flags) ουτως ώστε αυτά να δημιουργηθούν κατα την αναπαραγωγή.
Το dvd έχει σχεδιαστεί σαν pal/ntsc.Εσωτερικά αποκωδικοποιείται κανονικά σαν 50/60hz πεπλεγμένο pal/ntsc και μετά ταΐζεταί στον deinterlacer.
Παναγιώτη,αντιστοίχως τα player που θα έρθουν εδώ θα μπορούν μεσω του 4% speedup και 2-2 pulldown να βγάζουν 1080p 50fps.Δεν υπάρχει λόγος να είναι αποθηκευμένη η πληροφορία στα 25fps.
Στα dvd αυτό γίνεται γιατί το βίντεο είναι pal.Στο HD όμως είναι καθαρό υψηλής ανάλυσης σήμα,χωρίς κουσούρια του παρελθόντος.
Γι`αυτο έγραψα οτι απο το καθαρό 1080p24fps μέσω hardware θα παίρνουμε οτι υποστηρίζει η οθόνη/προβολέας μας.Pal για απλές συμβατικές συσκευές,Hd downconverted και με αλλαγή fps για HD συσκευές.