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Burning BDs from 1920×1080 50p
I am currently using a Sony HX100 for filming in 1920×1080 50p (PS mode 28Mbit/s) and burning these on to a Blu Ray in Vegas Pro 10. As yet BDs (Blu Rays) don´t seem to support this format in Mpeg 2 (although some people claim that it does i.e. Vegas) so all authoring/burning progammes seem to down convert from 50p to 50i.
Does anyone have further information on this and do any BD players play 1920×1080 50p in Mpeg 4? It would seem preferable to burn in Mpeg 4 since no conversion to Mpeg 2 would be necessary. As far as bit rate is concerned 28Mbit/s is no problem for BD players since these cope with up to 54Mbit/s. All that would be required from the BD-player is a software update like the one used for BDs to accept HDV-files a few years ago.
PMB does burn in Mpeg 4 but not 28Mbit/s i.e. “PS”. Is PMB being upgraded to burning in “PS2 28Mbit/s? BD-players would have comply as well of course.
When you go from 1920X1080 50i to 1920×1080 50p the bit rate increases fom 24Mbit/s to 28Mbit/s, does this not entail heavier compression for each frame?
The luminance frequency doubles when you go from i to p and the GOP would also be affected I suppose. Does 50p really only benefit moving objects in the picture. I think most computers struggle a bit with rendering 50p smoothly in spite of state of the art CPUs/GPUs, whereas BD players seem more bespoke for video which is rather expected but as yet I´m not sure they deal with 1920×1080 50p at all one is left with a certain amount of uncertainty.
At retail level one gets no help at all and Sony support is rather vague on the subject.
Burning in lower qualities like 17Mbit/s or 1280×720 is out of the question due its poorer picture quality like DVD which is totally insufficient for all HD work.
ESF
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5 Replies
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[Sigfrid Nordström] “I am currently using a Sony HX100 for filming in 1920×1080 50p (PS mode 28Mbit/s) and burning these on to a Blu Ray in Vegas Pro 10. As yet BDs (Blu Rays) don´t seem to support this format in Mpeg 2 (although some people claim that it does i.e. Vegas) so all authoring/burning progammes seem to down convert from 50p to 50i. “
That’s correct…1080/50p is not a supported Blu-ray format. You can convert to 1080/50i or 720/50p, your choice. It’s not possible to update most Blu-ray player for 50p or 60p, that would require twice the decoding rate they currently support. Technically speaking, any BD player capable of 3D support should be pretty close to allowing 50p/60p, but sadly, while the 3D profile did increase the speed and maximum bitrate permitted for 3D discs, it did not add a 50p/60p mode.
[Sigfrid Nordström] “When you go from 1920X1080 50i to 1920×1080 50p the bit rate increases fom 24Mbit/s to 28Mbit/s, does this not entail heavier compression for each frame? “
Of course, camcorder bitrates are dictated by standards and capabilities of the current hardware. But sure, that is the case… 28Mb/s for 1080/50p delivers a lower per-frame bit budget than 24Mb/s for 1080/50i.
That’s probably ok, though, at least most of the time. The way MPEG standards work, they encode a single “I-Frame”, for “Independent”. This is like a single frame in DV or Motion JPEG. For subsequent (usually at least 15) frames, the image stored is based on previous (and possible subsequent) frames. The MPEG algorithm runs a motion estimation algorithm, which encodes “motion vectors”… take frame N, calculate how to change it to frame N+1. Now, take just the difference between that calculated frame and the actual one, and that’s all you have to store (well, along with the motion vectors).
When you’re recording at 50p, you have twice the frame rate. So, all things being equal, objects only move half as much from frame to frame… so you can use fewer bits per frame to encode the differences. And errors are only on-screen for half as long, so it’s more forgiving based on time, too.
We’ve seen this before. MPEG-2 on DVD is usually encoded at around 7-8.5Mb/s, give or take. HDV is encoded at 1440×1080, four times the data of a DVD per frame. So we’d like to see 28-34Mb/s on the average. But we only get 25Mb/s for HDV. Going to ATSC television, we’re actually recording six times the data of a DVD per frame, 1920×1080 and that’s down to 19.4Mb/s or less in the stream.
And similarly, that’s pretty much ok. An HD image is broken up into many, many more DCT blocks than an SD image, and each is visually much smaller. So for the same image, we’ll have far less information in each block, and even though HD will put more detail in the overall image, we’re much less sensitive to defects in the smaller details. So we can get away with a bit less of a bit budget per DCT block.
Of course, some cameras will use more bits anyway. 25-28Mb/s AVC is an improvement over MPEG-2 at 19-25Mb/s. But of course, you can get better results with higher bitrates for either. Most higher end pro cameras go for higher-still bitrate MPEG-2 (35-50Mb/s) rather than AVC. This is part just because of momentum — AVC encoders are computationally more complex, and still improving, while MPEG-2 is mature. And many higher end pros have a well established MPEG-2 toolchain.
-Dave
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Thank you Dave!
It is fairly much as I thought. One is just tempted to think that BD players going up all the way to 54Mbit/s would be easily converted to cope with 28Mbit/s in Mpeg 4.
One wonders how Sony thought when they implemented the “PS 28Mbit/s” mode for their whole range, since the BD standard does not comply with it. It looks good on the fact sheet I suppose and possibly a new BD standard is just round the corner?
Possibly you can work out a bespoke PC to render 1080 50p but most people seem to think PCs would struggle with this and PCs are not the right environment in this case. Any hard drive storage is of doubtful stability in a long term perspective. This is where BDs make sense along with being fairly cheap and versatile to use.
If you start with a more aggressive form of compression in 50p and then transform it into 50i (also going from Mpeg 4 to Mpeg 2) would it not seem better to shoot in FX mode (24Mbit/s) and burn it to a BD in Sony´s PMB which I think leaves it in Mpeg 4? Having said that, in support of the first method, 1080 50p burnt into 1080 50i each frame becomes a field which would perhaps make some sense?
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[Sigfrid Nordström] “It is fairly much as I thought. One is just tempted to think that BD players going up all the way to 54Mbit/s would be easily converted to cope with 28Mbit/s in Mpeg 4.
“Generic BD players, probably not. Though I would venture a guess that any BD player capable of 3D output should have enough computational power to do a single stream at 1080p. Certainly the PS3 could support it… that’s why I was kind of surprised that they didn’t roll 1080/50-60p support in with the 3D update. Oh well…
[Sigfrid Nordström] “One wonders how Sony thought when they implemented the “PS 28Mbit/s” mode for their whole range, since the BD standard does not comply with it. It looks good on the fact sheet I suppose and possibly a new BD standard is just round the corner? “
I don’t think so… they’re basically just following the competition. Panasonic’s had 1080/60p for at least a year-and-a-half now in some models, even Sanyo had it. There’s nothing in current camcorders directly related to Blu-ray.
The AVCHD standard was derived from Blu-ray, but it was scaled way down to be useful for camcorders, including DVD, Blu-ray, and flash media models. The cap on that standard is 24Mb/s, so unless there’s a reason to change that limit, no one does.
1080/50-60p provided such a reason. Panasonic came out at 28Mb/s, so it’s no big surprise that Sony would go there too. That’s not AVCHD, but it can’t be anyway, since 1080/50-60p is not an AVCHD-legal resolution anyway. This still keeps recording just dandy on a Class 4 SDHC card (which can technically support up to 32Mb/s).
I suspect these rates eventually move on up. Many DSLRs are already shooting at much higher rates in AVC for video… they don’t shy away from demanding faster memory cards to keep up.
[Sigfrid Nordström] “Possibly you can work out a bespoke PC to render 1080 50p but most people seem to think PCs would struggle with this and PCs are not the right environment in this case. Any hard drive storage is of doubtful stability in a long term perspective. This is where BDs make sense along with being fairly cheap and versatile to use.”
I can do 1080/60p on my 2-core laptop using GPU acceleration for rendering… it’s not THAT difficult. But keep in mind, a PC is supposed to be a general purpose computational device. BD players are very tightly designed to the job that’s fully qualified for them up front… unless you’re running on a game machine like the PS3, which is also designed to be general purpose (and, not surprisingly, takes about 10x the power to run, versus a dedicated BD player… it does all decoding in software, versus fixed hardware for the BD player).
Hard drive storage has its limits. They are fairly reliable, and if you treat them as a storage media rather than an archival media, they’re fine. You can certainly burn 1080/50-60p video file to BD for backup, just not as BDMV discs that will play on regular players. I think right now it’s actually the case that HDDs are still as cheap, give or take, as BD storage, but that’s not likely to last. Still, when I first started making Blu-ray discs, I calculated that the HDD storage I would need to store a season of a TV show (I was using “Lost” on Blu-ray as a model) actually cost me more than the Blu-ray set did… that’s one of the real problems with online purchases of video (assuming they actually sold you BD quality video, which they never will). But a media PC isn’t a horrible idea for showing your own videos.. I use my PS3 for this, though getting it to play 1080/60p is questionable right now, largely because its not something Sony seems to care about.
[Sigfrid Nordström] “f you start with a more aggressive form of compression in 50p and then transform it into 50i (also going from Mpeg 4 to Mpeg 2) would it not seem better to shoot in FX mode (24Mbit/s) and burn it to a BD in Sony´s PMB which I think leaves it in Mpeg 4? Having said that, in support of the first method, 1080 50p burnt into 1080 50i each frame becomes a field which would perhaps make some sense?”
I’m never going to burn directly from the camcorder files anyway, since I always edit. So the camcorder format isn’t important to me, but yeah, you ought to be able to take raw video from any AVCHD camcorder and burn directly to compliant Blu-ray without re-encoding, given that AVCHD is largely a subset of Blu-ray (AVC is also know as MPEG-4 part 10, but most of the time when people say “MPEG-4” video they’re referring to MPEG-4 part 2, also called MPEG-4 Advanced Simple Profile… so be careful about causing confusion. “AVC” or “H.264” are more commonly used).
If you know for certainty that you want 1080/50i, shoot in 1080/50i. The advantage of shooting in 1080/50p, even for Blu-ray, is that you decide later if 1080/50i or 720/50p was the right answer for the material you shot. And you get the archival format as well… 1080/50p may be more useful in the future, maybe the next time a Blu-ray upgrade rolls around.
We shooting in NTSC-land formats have an advantage, since most NTSC camcorders will also shoot in 1080/24p mode.. not sure if that’s as well established in the former PAL territories (the frame rates survive, but both NTSC and PAL themselves are dying off fast). I shoot 24p for a film-like look, and as well for low-light… I can shoot at 1/24th second at 24p, but only down to 1/60th second for 60i or 60p.
The bitrate isn’t the limit… any BD player can certainly decode 54Mb/s or whatever the limit is these days… 3D players are required to decode up to 70-something-Mb/s. The problem is whether they can actually decode twice as many frames per second. The data rate is really a function of a the medium (eg, the Blu-ray disc player mechanism), while the decoding rate is largely a function of the processor in the BD player.
-Dave
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Thanks again Dave!
I just wonder why Sony went out with the logo “AVCHD Progressive version 2.0”. Some say it will come on all new BD players and that there will be an update for most older BD players. I don´t know if this has any relevance for anything of what we talked about and what it entails?
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Cool! I didn’t actually know about that one.
I guess, basically, because Panasonic did 28Mb/s 1080/60p in early 2010, but they didn’t dub it AVCHD. The format is exactly what you’d expect for AVCHD… I’m pretty sure it’s AVCHD 2.0 compliant, after the fact.
Of course, Panasonic and Sony created the AVCHD spec out of the Blu-ray spec. But this doesn’t actually change anything for disc media.. the limit for DVD is still 18Mb/s, and there’s no support for AVCHD on Blu-ray media. So this is a memory card thing only, far as cameras and players go. Nearly every current BD players supports AVCHD (it’s kind of crazy, in fact… most will not play a BDMV on DVD, but put that same video on the slightly different AVCHD file structure, and nearly all BD players handle it).
Of course, if you do see a Blu-ray player with the “AVCHD 2.0” label on it, you know it’ll play 3D and 50p/60p.. but not necessarily from BD or DVD. But it certainly COULD play it from BD, given a modified spec. As I said, I was surprised they didn’t include 60p in the 3D Blu-ray spec, since at that point, the hardware is effectively doing the same thing (the AVC-MVC format is actually using only 50% more data than 2D, but the computation is likely to be slightly more than twice as much to decode).
-Dave
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