You are here

Is HDMI recording better than tape?

Jaimie's picture
Last seen: 1 year 2 months ago
Joined: 10/14/2009 - 1:25pm

I read somewhere that using an external disc drive results in a higher quality (i.e. wider bandwidth) recording than camcorder records on a miniDV tape. I use Sony HVR z5u and Z7u cameras so this is of interest to me. But, I'm not sure it's correct. The premise is that the HDMI port is very wideband capable and the external recorder is also capable of wideband recording, therefore, you can get higher quality footage by using an external disk recorder connected to the camera's HDMI port.

My question is, is the bandwidth of the signal at the HDMI port actually greater than that recorded on the tape? Is the compression algorithm applied to signals destined to be recorded on tape the same as the algorithm applied to signals going to the HDMI port?

The camera specs don't provide any guidance.


Rob Grauert's picture
Last seen: 2 months 3 weeks ago
Joined: 02/16/2008 - 10:47pm

"My question is, is the bandwidth of the signal at the HDMI port actually greater than that recorded on the tape?"

The short answer is yes. HDMI is capable of giving you better quality than tape.

BUT, it depends on the codec you are recording on the external recorder and it depends on the tape format you are comparing it to, but since you mentioned miniDV, I'll assume we're comparing to that.

HDMI has evolved over the years to support better quality video - HDMI 1.0, 1.2, 1.3, & 1.4.

In short, if your camera has HDMI 1.3 or 1.4 output, and your recording device has HDMI 1.3 or 1.4 input, then it is certainly capable of recording MUCH better quality than miniDV, given that you're not recording a highly compressed codec.

Im reading a book on color correction that touched on this, but I left it at work. So I can give you more details tomorrow.


Rob Grauert's picture
Last seen: 2 months 3 weeks ago
Joined: 02/16/2008 - 10:47pm

Ok, so this is what is possible out of HDMI:

All versions of HDMI (1.0, 1.2, 1.3 & 1.4) support SD and HD @ 8-bit.

HDMI 1.3 began supporting bit depths greater than 8-bit. 8, 10, and 12-bit Y'CbCr signals and 8, 10, 12, and 16-bit RGB signals.

HDMI 1.3 supports 4:2:2 and 4:4:4 Y'CbCr signals and 4:4:4 RGB signals

HDMI 1.3 supports up to 2560x1600 resolution.

HDMI 1.4 introduce support for 3840x2160 @ 24, 25, and 30fps. And 4095x2160 @ 24fps

So yes, Jaimie, HDMI is capable of carrying a signal that is much, MUCH better than what you get from miniDV tape. Just be sure that the device recording the HDMI signal isn't compressing that signal with a crappy codec.

And like I said, make sure the HDMI ports on both your camera and recording device are the same version of HDMI (or make sure the version on your recorder is a newer version than the camera's).


Jaimie's picture
Last seen: 1 year 2 months ago
Joined: 10/14/2009 - 1:25pm

Rob,

Thank you very much, I did not know any of that!

I checked the specs in the book that came with my camera, a Sony HVR-Z7u, and it doesn't say what version of HDMI it is using. It only specifies a "Type A" HDMI connection which I believe refers to the connector style. Further, the book does not address the compression used on the tape, chip recorder or the HDMI output.

If I might pick your brain a little more, do you know how I can determine if the video signal at the HDMI port is actually better (higher color depth, less compression wider brightness range, wider bandwidth, etc) than the same signal recorded and played back using the camera's internal HDV tape deck? My point is maybe the HDV tape is capturing all that the camera is capable of providing. If that is the case, there is no point in buying external wider bandwidth recorders because there is nothing more to capture. It would be like copying VHS tapes onto Blu Rays. The quality is still that of a VHS tape even though it is on a high def disc.

As an aside, I have not faced a quality problem yet as all my product has been supplied on DVDs. Nobody has ever wanted BluRay. Nevertheless, I find that editing at the highest possible quality level yields a better looking DVD. I have also found that the higher the quality of the original, the easier it is to fix up bad exposure, color etc.

Thanks again for your help,

Jaimie


Rob Grauert's picture
Last seen: 2 months 3 weeks ago
Joined: 02/16/2008 - 10:47pm

What's recorded to your HDV tape is a digital video signal that adheres to HDV Spec: 8-bit 4:2:0 MPEG2 compression. Also keep in mind that MPEG2 compression utilizes Long GOP compression.

HDMI Type A is HDMI 1.0. It will give you 8-bit color depth and Ithink 4:2:2 chroma subsampling. In addition, if you go into an external recorder, you can record an I-Frame codec instead of a Long GOP codec.



SafeHarbor's picture
Last seen: 1 day 17 hours ago
Joined: 01/22/2010 - 3:28pm

Hi Jaimie,

Good advice from Rob. Note that HDV recordings use the same amount of space that a DV recording did - this should give an indication of how compressed the video is, fitting 1080 HD into an NTSC space! As mentioned, HDV uses 4:2:0 color and the Long-GOP compression only records TWO full frames per second. The rest of the frames only record partial data - the changes taking place between the full frames - and these partial frames then need to be reconstructed by fetching bits from the frames before and after during playback. A real mess. HDV can look great, until you get a lot of detail and motion going on, then it falls apart.

When shooting live video, the HDMI signal coming out of the camera has NOT yet had the HDV compression applied - it is an "uncompressed" 1920x1080 video with 4:2:2 color. Keep in mind that HDV records to tape as 1440x1080, so there's extra resolution coming out the HDMI port as well! An external recorder like the Atomos Ninja will record that clean HD signal to the lossless Apple ProRes 422 10-bit codec at selectable data rates of about 100, 150, or 200Mbps versus the 25Mbps of HDV. Obviously quite a bit more information being recorded, and the video will show it.

The external recorder also allows for long, uninterrupted recordings - up to 11 hours with Ninja! I have shot many stage events with Ninja running 2-2.5 hours without issue. I run HDV tape at the same time for backup, and Ninja continues recording smoothly while changing tapes.

Don't confuse devices like Ninja with the recorders from Sony and others that connect via 1394 and simply record the SAME HDV DATA externally. You get the convenience of the solid-state recording, but with the exact same highly compressed footage that you record to tape.

Thanks

Jeff Pulera
Safe Harbor Computers


Jaimie's picture
Last seen: 1 year 2 months ago
Joined: 10/14/2009 - 1:25pm

Thanks Jeff,

I haven't had any problems with the HDV format except that I noticed that recovery from a dropout takes quiet a few frames. I generally record on a chip using the Sony MRC recorder and on tape, too.

I got interested in the HDMI output when I read that green screening can sometimes experience artifacts with HDV and the 4:2:0 compression due to the low color resolution. I haven't done any green screening, yet, so I don't speak from experience. But it may come up.

I do all my editing with Adobe Premiere Pro on a PC with IEEE1394 and USB2.0 and 3.0 inputs. I have no problems capturing by playing tapes back in the camera connected to the PC via IEEE1394. How do you get the content from the Ninja into the editor? It looks to me like you just remove the Ninja's hard drive and connect it to the PC. That would be perfect. But, file transfer is fine, too. I am not a fan of real-time transfer which I'm stuck with using tape.

Thanks in advance for all your help.


Rocky M's picture
Last seen: 1 month 1 week ago
Joined: 03/12/2010 - 5:53am

Another aspect of tape v HDMI is that tape requires mechanical components. Whilst tape decks employed in video recording devices today are reliable they are by design subject to wear and tear.Adverse weather/environmental conditionswill also more readily effect tape decks.I record withHDMI and tape simultaneously (tape used for back up) and what is interesting is that when both recordings are placed in the same PAL 25 fps timeline, there can be aseveral frames differenceat the end of a 30 minute recording. The HDMI was found to be the accurate time recording.


Jaimie's picture
Last seen: 1 year 2 months ago
Joined: 10/14/2009 - 1:25pm

I agree that the tape transport is a possible source of problems, especially as it ages. Currently, I record on chips using the Sony MRC recorder and on tape for backup. If I find I can use tape only, the problem is twice as serious because I play the tape back in the camera to capture it in my editor. The effect is to put twice the wear on the camera's tape transport.

That's interesting about the lengths being different. I haven't seen that problem with chips versus tape recordings, but neither involves HDMI and I use 1080i.


SafeHarbor's picture
Last seen: 1 day 17 hours ago
Joined: 01/22/2010 - 3:28pm

Hi Jaimie,

The Atomos units come with a Drive Dock which has Firewire 800 for Mac users and USB 3.0 for PC users. Pop the drive out of the Ninja or Samurai and into the dock for immediate editing (or copy to internal drive on edit machine).

Jeff Pulera

Safe Harbor Computer


Jaimie's picture
Last seen: 1 year 2 months ago
Joined: 10/14/2009 - 1:25pm

Thanks!