XDCAM HD at 25 Mb is HDV?

[Greg Sherris]

I'm looking to confirm that XDCAM HD is HDV when recording at 25 Mb CBR. Media Composer (2.6 Software only version) on a G5 exhibited playback errors at the 1080i 59.94 HD project settings which were cleared up when the format was changed to HDV.

As for output, one of our recent projects downconverted to SD with letterbox for writeback to DVCAM tape nicely, but another project would not transcode properly, and mixing down to SD would not work properly. Error message said that there were still SD and HD files mixed together so digital cut back to the deck wouldn't work. I'm wondering if anyone has had similar problems.

BTW, we resolved the error above by exporting quicktime and importing that file into a different SD sequence. It was a lengthy and somewhat awkward addition to what should be a pretty straight-forward workflow.

We are not knocking XDCAM HD. SD production with our three 330s has been flawless. HD production has only just begun and we are having initial learning curve issues with post in HD. XD is thus far an excellent camera system.

thanks in advance for any info

[Greg Boston]

It bears a similarity to HDV @ 25mb CBR, but with higher native pixel count than most HDV cameras and larger sensors, there's more to work with coming from the camera head that results in a superior image to HDV.

Also, per the specification, a camera branded as HDV must record to tape on a mini-dv type transport.

-gb-

[Greg Sherris]

Thanks for the reply. I'm afraid I wasn't very clear in my original post. The camera head is clearly superior to any HDV camera of which I am aware, and XD is not tape, but will editors such as Composer handle the 25 CBR 59.94 1440x1080i recording as HDV even though the camera files are imported and are MXF as opposed to ingested via firewire AV/C? I was a bit surprised that the editor exhibited playback problems with the 1080i 59.94 HD project settings, but played back under HDV settings. Any thoughts or similar experience?

[Simon Wyndham]

but will editors such as Composer handle the 25 CBR 59.94 1440x1080i recording as HDV even though the camera files are imported and are MXF as opposed to ingested via firewire AV/C?

I'm still not sure what you mean? If Composer is designed to take XDCAM files then yes, it will handle the footage. But if it doesn't then it won't read the files at all. Remember also that XDCAMs audio is uncompressed, and by default it is set to record 4 discrete channels. Perhaps if you record your footage with the camera set to two channels it might reduce the burden on your machine slightly?

[Bob Willis]

From the somewhat limited information I can gather from Sony and Avid on the subject here is what I have found.

XDCAM HD recorded at 25Mbps in 1080/60i is Constant bit rate and should be brought into anAvid project as 1080i HDV.

XDCAM HD recorded at 25 or 35Mbps at 1080p/23.98 is variable bit rate and should be brought into an Avid project as 1080p 23.98.

Files brought over firewire (or Ilink) as FAM (file access media) will be native resolution. Video brought in over firewire as AV/C from the deck or camera is downconverted from MPEG HD to DVCAM (Unless originated as DVCAM).

Does this sound correct to other Avid people out there?

[Bob Willis]

So to answer your question Greg, the 25Mbps 1080/60i files should be brought into Avid as a 1080 59.94 HDV project.

Any thing shot at 23.98 should be brought in as 1080p/23.98 project.

[Greg Sherris]

Thanks Bob - good info to have

We've had great success with SD DVCAM files and with doing HD to SD downconvert in the camera over firewire - just working out a few FAM questions for HD file import.

[Greg Boston]

Originally Posted by Bob Willis

XDCAM HD recorded at 25 or 35Mbps at 1080p/23.98 is variable bit rate and should be brought into an Avid project as 1080p 23.98.

35 and 18 are VBR, 25 is CBR, regardless of the frame rate. However, if you overcrank beyond 30fps, the camera's vertical resolution drops to 540 and the resulting bit rate is 17.5 (half of 35).

-gb-

[Bob Willis]

Greg B., I would love to get this issue resolved. I expressed these exact fiqures to Avid engineers (who are working with Sony) and they state that XDCAM HD 25Mbps shot at 1080p/23.98 is variable bit rate and should be brought into an Avid project as 1080p/23.98 not a HDV constant bit rate project.

This might be a misunderstanding between engineers, but I would love to get an answer. Maybe it is a non-issue as most people will be shooting at 35Mbps for a 1080p/23.98 project anyway. That we know is VBR.

This may be an incompatibility issue between Avid and Sony. I'm not sure. Any additional incite would be appreciated.

[Greg Boston]

Agreed, this needs to be cleared up. The bit rate should be constant at 25mb. In fact, I believe they put this mode on the camera for compatibility with NLE's that can handle HDV although the audio is uncompressed 48/16 unlike HDV which uses mpeg compression of the audio.

Greg's statement seems to confirm that notion...

... a G5 exhibited playback errors at the 1080i 59.94 HD project settings which were cleared up when the format was changed to HDV.

Honestly though, I don't use Avid so I can't confirm this. I will talk with the Sony folks Monday morning and will attempt to do some of my own experiments in the meantime.

-gb-

[Greg Sherris]

Originally Posted by Simon Wyndham

I'm still not sure what you mean? If Composer is designed to take XDCAM files then yes, it will handle the footage. But if it doesn't then it won't read the files at all. Remember also that XDCAMs audio is uncompressed, and by default it is set to record 4 discrete channels. Perhaps if you record your footage with the camera set to two channels it might reduce the burden on your machine slightly?

Here is some more info and maybe you can and others can help shed some light. BTW Media Composer is designed to take XDCAM HD files. We run Composer software only version 2.6. on the G5 and on PCs. Both work very well - stable on both platforms. Composer is Xpress Pro's big brother (according to some users). As well, our cameras are set up for 4 channels in HD. Here is where it gets odd. Two projects - both shot at 25 Mb CBR 59.94. Both imported using identical approaches using the same user and site settings and 1080i 59.94 HD Avid project settings. One project works flawlessly for playback and editing of clips and playback of sequences, the other project exhibits an error on playback, which is cleared up when we switch from 1080i 59.94 HD settings to 1080i 59.94 HDV settings. Clip playback, editing and sequence playback works after that change. I'm away from the edit suites so I can't quote the exact error message. When we have a lot more time than I have at present, I'm going to run a series of trials to learn more and diagnose the problem. I'm going to try changing between 2 and 4 channel audio at that time - the G5 has only 1 GB of RAM as opposed to 2 GB min recommended, but if the machine is underpowered, then why one project and not the other?

thanks for any input and feedback

[Daniel Aleksic]

Yes, HDV is 25mbps, however even at 35mbps its still HDV. I have had great experience using the X2 to import XDCAM footage at any bitrate as the matrox X2 can handle HDV from 25 to 100mbps. I wonder if that's an indication that XDCAM might be available in higher datarates on their new 2/3" XDCAM Camera.

I believe HDV at 25mbps has too much compression, even at 35mbps, so maybe a 50mbps codec will look much better...

[Greg Boston]

Originally Posted by Daniel Aleksic

Yes, HDV is 25mbps, however even at 35mbps its still HDV.

Sorry Daniel, that's not correct. By definition, HDV is 25mb CBR, along with other criteria. Anything else IS NOT HDV.

The problem seems to be what criteria people assign to HDV vs. HD. I only go by the official specs which state that it has a bitrate of 25mb CBR and utilizes a mini-dv tape and transport for recording. Without those two properties, the official HDV logo cannot be used on the camera. Just because it's based on MPEG2 doesn't make it HDV. If that is the case, then all broadcasters are broadcasting HDV because it arrives OTA as an MPEG2 Transport Stream.

This camera produces imagery and audio that is superior to HDV. It is a mid level HD product for Sony. Most who have used and seen what the camera and format can do place it closer to the high end HDCAM than the lower end HDV.

-gb-

[Alister Chapman]

I think your problem is the lack of RAM and is being cause by the way Avid treats the frame sizes of HDV and non HDV projects. When working with an HDV project everything is treated as having a Frame size of 1440x1080 with anamorphic pixels (thin raster) and then simply stretched to the correct aspect ratio for playback, all effects, renders etc are 1440x1080 thin raster. There are even special "thin raster" versions of the DNxHD codec to keep everything the same size/aspect ratio.
With a non HDV project ie 1920 x 1080 DNxHD, the projects native frame size is 1920x1080 with square pixels, so any HDV or native XDCAM material is scaled from 1440 Thin Raster to 1920 square pixels BEFORE any additional processing. This adds an additional load on the CPU/RAM and may explain your playback issues. If you are working on a project that is primarily HDV or XDCAM material you should use the HDV preset to reduce any artifacts being introduced due to the additional scalling in a 1080 project.

[Alister Chapman]

XDCAM at 35mb is VERY different to HDV. The dynamic allocation of data in the VBR stream to where it is most needed makes a big difference to the reduction of artifacts. Look at the psots in this and other XDCAM forums and you'll almost never see anyone complain about artifacts even shooting under extreme conditions. Bigger worries are lens quality and optics, in fact the limiting factor with XDCAM HD appears to be optics and not the codec or disk system and you certainly can't say that about HDV.