Sony HVR-25 series - DV tapes using HDMI out

[Jared]

I have a HVR-25AJ and have been capturing DVCAM tapes via it's HDMI output and BM HDMI recorder. Can anyone tell me what the deck is doing to this signal? It looks pretty good-- much better than using component. I have the manual but don't see a detailed explanation.
Thanks
Jared

[DB83]

Pray tell what a HVR-25AJ is.

But you sure hardly have DV video now. Maybe HDV ?


But to be certain just upload a short sample of the video created by this arrangement.

[Bwaak]

The deck reads digital video off the tape. Then I suppose it decompresses it and sends uncompressed via HDMI. An unnecessary waste of space.

[Skiller]

DVCAM should not be captured (be it via HDMI or Component), but streamed to a computer in it's native format which is DV.

[dellsam34]

It looks pretty good-- much better than using component. I have the manual but don't see a detailed explanation.
Thanks
Jared

You might be right, because component is analog and converting DV/DVCAM/HDV to analog is a lossy process, so keeping it digital using minimal processing via HDMI keeps it somehow good, But you know what is the best method? Transfering the footage as is from tape to hard drive without any processing, You would need a firewire port on your computer, a firewire cable, a piece of software for DV/DVCAM called SCLive and another piece of software called HDVSplit for HDV.

[dellsam34]

Pray tell what a HVR-25AJ is.

But you sure hardly have DV video now. Maybe HDV ?

I think he has a Japanese version, But all versions playback and record DV/DVCAM/HDV in mini and full size cassettes:


[Attachment 76502 - Click to enlarge]

[Jared]

Thanks for the replies. Seems like it's not an easy answer.

DB83 - I capture the HDMI via Black Magic which allows capture in several codecs. Uploading the sample will only show what codec I chose to capture with.
Bwaak - "waste of space...". Well, this just depends on what codec I'm capturing at right? If I capture at DV, the data rate is basically fixed. Same with the Pro Res flavors.

Skiller & Dellsam34 - I had been capturing 100's of DV tapes natively(firewire) via DVRescue and Vrecord (mac) but I'm now having issues with both of these. The developers are working to fix these issues. I then tried HDMI to BM Recorder/Express encoding with Pro Res 422 (keeping the interlacing) and thought it looked great. It made me wonder if the HDMI was carrying the native DV signal...probably not. But if not native, what is it doing the the signal.
Thanks all.
Jared

[DB83]

Well you sort of answered your own question.

If you do not capture/transfer native DV you are the mercy of capture device/software. What else would you expect ?


In fact a 'true' answer would be to compare a native transfer with whatever else you choose to do.

[Jared]

Well you sort of answered your own question.

If you do not capture/transfer native DV you are the mercy of capture device/software. What else would you expect ?


In fact a 'true' answer would be to compare a native transfer with whatever else you choose to do.

I 100% agree with you here. I haven't been able to do a deep comparison between the two -Native/Firewire vs HDMI (to DV or Pro Res) as my HDMI deck has died on me just recently. And my Firewire capture software isn't currently working. I prefer the HDMI/Black Magic workflow and thought I'd just try to understand it better.
Thanks
Jared

[Cornucopia]

To answer one of your questions: HDMI does NOT support streaming of pre-compressed material in any form. ALL HDMI signals are uncompressed.* So it isn't possible to get an exact copy of the already DV-encoded data on tape at the input of your BMD's HDMI input.


Scott
*not counting obviously color subsampling, and the new v2.1 DSC (display stream compression) which is a transmission-only compression for 8k material, giving ~2:1 compression.

[Jared]

To answer one of your questions: HDMI does NOT support streaming of pre-compressed material in any form. ALL HDMI signals are uncompressed.* So it isn't possible to get an exact copy of the already DV-encoded data on tape at the input of your BMD's HDMI input.


Scott
*not counting obviously color subsampling, and the new v2.1 DSC (display stream compression) which is a transmission-only compression for 8k material, giving ~2:1 compression.

Thanks Scott. That question was nagging at me for a while.

[dellsam34]

I had been capturing 100's of DV tapes natively(firewire) via DVRescue and Vrecord (mac) but I'm now having issues with both of these. The developers are working to fix these issues. I then tried HDMI to BM Recorder/Express encoding with Pro Res 422 (keeping the interlacing) and thought it looked great. It made me wonder if the HDMI was carrying the native DV signal...probably not. But if not native, what is it doing the the signal.

What you are doing in hardware is pretty much most of us do in software, I thought my answer above was clear but let me expand on it a little bit:

Your video is encoded into DV on tape, so when the deck reads the tape it streams it via firewire with no alteration, despite being a lossy codec but untouched nevertheless. Then another branch goes to a DV decoder chip inside the deck to strip down the codec and send an uncompressed stream out to HDMI port for display purposes, keep in mind HDMI was never designed to be captured, It made possible for videogamers to record their experience.

Most people use software approach, meaning transfer DV to HDD as is, Use a software to strip down the DV codec (usually vdub2) to get an uncompressed AVI file or a lossless compressed file such as HuffUYV.

Now here is the most important part where software is better:

How do you know what bitrate the DV decoder is processing the signal at? 6bit, 8bit, 10bit...etc and what color sampling rate? 4:2:0, 4:2:2, 4:4:4, you would never know even if you have the chips datasheets, because the designer can change those numbers at the output pins. In software you get to decide what those values should be.

Not sure why you have to use DVDrescue, I've been using SCLive with no problems at all, occasionally when I get a dropout, I recapture only the affected section and insert it in the timeline with vdub during the processing with no re-encoding or loss of quality.

The same for HDV, But being MPEG2 4:2:0 1440x1080 16:9 the process in software is a little different than DV.

[Jared]

Thanks Dellsam34. I appreciate the details of your response. My original question was, "what is the deck doing to the signal?" and it seems that the answer is... "who knows?". But even without n clear answer, I appreciate your breakdown.

- Re software & DVRescue, I'm a Mac user. Doesn't look like SCLive and Vdub support mac.

When I get my Firewire workflow working again, I'll try some tests for fun.
Thanks again.

[Bwaak]

My original question was, "what is the deck doing to the signal?" and it seems that the answer is... "who knows?".

Who knows, really? You have DV or HDV on tape. The deck reads the digital data off the tape. Then it uncompresses it and sends over HDMI as uncompressed. The only question is, whether it always sends it as HD (in this case it will also scale it up), or it can send DV as SD (too lazy to check the manual). Then you get uncompressed video on another end, which you can compress using another codec if you like, or you can keep it uncompressed. If you keep it uncompressed, you have the same quality as on tape, but in a larger file. If you compress it, then depending on the codec and the bitrate, you will lose more or less of the original quality.

To grab it in the original quality without recompression, you need to send it over Firewire, which will send DV or HDV as is, then it will be saved into a DV-MOV or DV-AVI as is, save for the container differences.

[Jared]

My original question was, "what is the deck doing to the signal?" and it seems that the answer is... "who knows?".

If you keep it uncompressed, you have the same quality as on tape, but in a larger file..

Hmm. Seems unlikely no? It was my original hunch and Dellsam34's reply seems to point out that a decoder's processing could introduce quality issues (lower bit rate and chroma subsampling) prior to sending the uncompressed video.
In my case, it looks good and I suspect it's equal or higher than DV standards. I was hoping one of ya'll would know but after reading Dellsam34's reply, I understand it is probably not something I'm going to figure out and will use my eyes instead.

FWIW, it's not getting upscaled to HD.

[Cornucopia]

Not higher. It can't create accurate data out of nothing. At best it is equal, but depending on chroma upsampling it might be worse. How much worse is open to interpretation (likely better than the roundtrip to analog), and you seem to think it's sufficient.
Regardless, the capture at the other end sounds lossy, even if prores. Again, it might be sufficient for your purposes, but bits is bits, and they come into play with downstream processing and/or recompression.


Scott

[Jared]

Not higher. It can't create accurate data out of nothing. At best it is equal, but depending on chroma upsampling it might be worse. How much worse is open to interpretation (likely better than the roundtrip to analog), and you seem to think it's sufficient.
Regardless, the capture at the other end sounds lossy, even if prores. Again, it might be sufficient for your purposes, but bits is bits, and they come into play with downstream processing and/or recompression.


Scott

Ha...it's tough to articulate things on a forum! I meant that the decoder could be set to decode and process at a "Higher" bit rate & less subsampling than the original DV (8bit,4:1:1). And no I didn't expect improvement.
Thanks all.
jared