HPX170 Bitrate Question

[Thane Silliker]

From my reading of Steven Ascher's Book "The Filmmaker's Handbook," the bitrate of the DVCPRO HD codec is 100 Mbps. However, I was just talking with a nearby dealer in Toronto who just told me over the phone that the DVCPRO HD codec that the HPX170 records on P2 cards is actually 50Mbps.

Specs from Panasonic also claim 100Mbps here:

ftp://ftp.panasonic.com/pub/Panasoni..._specsheet.pdf

Look on page 6.

So is the sales rep in Toronto in error? I don't want to start another specification m@&turb@t!on session, but just trying to clarify a point that is a bit unclear.

Pretty impressive if it is - an inexpensive camera that can record 100Mbps interframe 4:2:2 codec.

[Ron Wilk]

You may be referring to the difference between DVCPro50 and DVCPro HD(both of which are available on the 170) DVCPro HD is also referred to as DVCPro100 for which Panasonic claims a bit rate of 100mbs on the hpx170. There are some posters who seem to feel that the actual bit rate is something less than 100mbs but I will defer to the technocrats and, of course, Panasonic for the correct answer.

[Dan Brockett]

The DVCPRO HD codec is standardized as a 100Mbit/s codec. However, the AG-HPX170 obviously is not recording at 100 MBit/s when it can record up to 42 minutes on a 16GB P2 card when shooting at 720 24pN. The native frames rates, 720 24pN and 720 30pN, record at a lower bit rate, not per frame, but as a stream in order to maximize P2 card space, recording time and to reduce post time by not having to remove frames when shooting 24p. Video data rate depends on frame rate and can be as low as 40 Mbit/s for 24 frame/s mode and as high as 100 Mbit/s for 50/60 frames/s modes. But your Toronto dealer should make it clear that the reduced data rate is only available when shooting 24pN and it is the same quality as when shooting 100Mbit/s, the data reduction is simply because the camera is shooting at only 24 progressive frames per second, hence the lower data rate. Still 4:2:2, still high quality, same compression.

Ron is correct about DVCPRO 50, an NTSC/PAL only codec. But DVCPRO 50 is not recording HD at that rate. The AG-HPX370, the next camera up the line, can record in AVC INTRA50, which is HD, but it is also 4:2:0 color space, which most Pansonic shooters aren't crazy about, but at least it gives you choices. I was told that AVC INTRA50 was included mainly for news shooters where color space is not usually a concern.

Dan

[Thane Silliker]

Thanks, guys. Yes, I would assume that at lower frame rates and resolutions, that the bitrate would be less.

I would assume the top bitrate occurs at 1080p 30fps, or I suppose 1080i 60 fields/sec, or likely even 720p 60 fps.

T

[Dan Brockett]

Top bit rate is at all 1080 modes since all 1080 modes are "over 1080 60i" and at 720 60p.

Dan

[Barry Green]

All 1080 modes are 100mbps.

720/60p or any of the 720p modes are also always 100mbps.

The 720pN modes are less, because it's storing fewer frames. DVCPRO-HD is an intraframe codec, not an interframe codec. The amount of bandwidth used for each frame is a fixed constant. So if you store half as many frames, it takes up half as much space.

[Thane Silliker]

Thanks, guys. I am happy to say I will be buying an AG-HPX170 this Friday!

[Jon Brady]

Is DVCPro50 on the 170/171 50mb/s? I'm really surprised I've not heard this before, since 50mb/s cameras are 'all the rage' at the mo (obviously)

Also, since the 170/171 is 1440x1080, does this not reduce the bitrate (from 100mb/s I mean)?

Is there anywhere that lists the bitrates for ALL recording modes on the 170/171 anywhere?

Any help much appreciated, thanks!

[David Jimerson]

Is DVCPro50 on the 170/171 50mb/s? I'm really surprised I've not heard this before, since 50mb/s cameras are 'all the rage' at the mo (obviously)

Yes.

But codecs are not all the same and a brand new, very efficient codec may actually give you the same or better quality at a lower bitrate than an older, less-efficient codec might. The bitrate itself doesn't tell the whole story.

Also, since the 170/171 is 1440x1080

Not so. The NTSC version of DVPRO100 1080 is 1280x1080. The PAL version is 1440x1080.

does this not reduce the bitrate (from 100mb/s I mean)?

No. The frame size has little to do with the bitrate.

Where you do see a bitrate save is in using the 720 "pN" modes, at 24p, 25p, or 30p, because it's recording fewer frames per second than the DVCPRO HD base of 50 or 60 fps, so while each frame has as much information in it, there are fewer frames. (Barry said so above. Wow, old thread.)