Compatibility of BDR-AVCHD discs

[ClassicalMan]

I see that my Panasonic DMR-BWT700 allows me to copy AVCHD files (camcorder footage shot in HD on a Panasonic X900 camcorder) to a BDR in high speed mode, i.e. in their original state as AVCHDs. Will such a disc play back in most (standalone) BD players, or only in Blu-ray recorders and certain computer BD drives? (I'm aware that I can make DVDR-AVCHD discs but the attraction of BDR-AVCHD would be the huge capacity, given that AVCHD is such an efficient codec - this would be preferable to burning AVCHD material to BDR in the DMR700's highest quality HD mode ('HG') in real time in terms of space usage (and dubbing time), but I wouldn't want to do so if there's very little playback compatibility outside of machines such as the BWT700.)

Thanks for thoughts from anyone who's done this and has relevant experience.

ClassicalMan

 

[ClassicalMan]

Since my post has elicited a less-than-extravagant number of replies, it may be that this question is of no interest to other users but, in case it is, allow me to note that I have now tried an AVCHD-BDR created on my Panasonic BWT700 (from camcorder footage in AVCHD imported from a Panasonic X900) on a 2010-era Sony Blu-ray player, and the disc played normally - the menu screen came up and playback was smooth. I had followed the BWT700's normal instructions to format the blank BDR when I first inserted it into the machine, and then copied the desired AVCHD files in high speed mode. My hunch is that this type of AVCHD-BDR disc will play back on more recent Panasonic and Sony Blu-ray players (since these manufacturers developed the AVCHD format), but this is only a guess. I don't have friends with other makes of Blu-ray player so cannot trial the disc in non-Sony/Panasonic machines.

ClassicalMan

 

[Gavtech]

Thanks for reporting your experiences.

 

[ClassicalMan]

One detail I forgot to mention that surprised me. The Panasonic X900 camcorder supports 1080/50i recording in ACVHD at up to 24Mbps but the BWT700 can only take an AVCHD file recorded at 18Mbps or less. For this reason I use the X900 in its 17Mbps mode (second highest quality mode).

Given that the AVCHD format was developed to minimise file size for a given HD picture quality, I expected a blank BDR to hold more footage in native AVCHD than in HG, the latter being the highest quality HD recording mode on the BWT700. However, the converse turned out to be the case. In other words, transcoding a given AVCHD file recorded at 17Mbps to HG mode slightly decreased the size of that file. It's been written elsewhere that the MPEG4 used by the BWT700/800/720 for HD is based on the same H.264 codec as AVCHD. So it's hard to understand why converting a file from what is only the second highest quality mode on the camcorder to the highest quality mode on the BWT700 (in what is a less efficient implementation of H.264) would result in a reduction in file size. I'm assuming this means that the BWT700 is losing some quality when transcoding in the way described (given that the AVCHD of the camcorder files is supposed to be the most efficient codec of all). Subjectively I've noticed a few apparent artifacts on the HG-mode conversions that do not appear to be there on the AVCHD originals, but these are so slight that I wonder whether it's my imagination! Any insights most welcome!

ClassicalMan

 

[KBeee]

filesize = bitrate*runtime - that's true for any codec
If your new re-encoded files are smaller than the original ones (and the play time is the same), then the new files have reduced the bitrate, which will reduce the quality in absolute terms. Whether that reduction is noticeable, or even important to you, only you can decide. The only way to avoid any quality loss, is a straight copy, rather than a re-encode, or to re-encode to a lossless codec which will make the new files much larger than the originals.

 

[ClassicalMan]

Yes, this was clear to me - the numbers speak for themselves, as it were. My curiosity is that apparently Panasonic have implemented a 'highest quality' mode for the BWT700/800 (i.e. HG mode) that is recording at a bit rate about 10% below the 17Mbps of the second-highest quality mode of their X900 camcorder. Given that AVCHD is apparently more efficient (in terms of data usage) than the 'straight' MPEG4 of HG mode, the 10% difference in bit rate is likely to be more significant than that in terms of actual quality loss. I'm curious as to why Panasonic has chosen a relatively low bitrate for its highest quality mode on the BWT700/800, relative to that of its own camcorders. Is it that Freeview HD broadcasts are not above 15Mbps, such that much more than that would be overkill (for HG)? I believe the new BWT720 will take AVCHD files recorded at up to 24Mbps (the highest quality mode for 1080/50i on the X900 camcorder) but, given its HG mode will be identical to that of the BWT700/800, there is likely to be noticeable quality loss for camcorder owners wishing to maximise their X900's potential by shooting in that 24Mbps mode and then transcoding to HG (in order to burn BDRs that have maximal replay compatibility).

ClassicalMan

 

[KBeee]

You are probably right about Panasonic deciding that the lower bitrate is "as good as it needs to be" for their highest quality recordings of Freeview HD broadcasts, the broadcast quality of which is outside Panasonics control, and tends towards the lowest bitrate the broadcaster can safely get away with. There comes a point when throwing more bitrate at an encode makes no noticeable difference to the final result, except to take up more space.
However, with their own camera they know the quality of the image it'll be capable of, and the bitrate needed to give the highest quality, and set the bitrate accordingly.

 

[ClassicalMan]

What you write makes very good sense. I don't want to knock Panasonic, since doubtless their Blu-ray recorders can hardly be big money spinners in the European market (given paltry sales volumes) and the consumer camcorder market has been badly hit by smartphones, but I'd have appreciated more joined-up thinking between Panasonic's product areas. Their camcorder group makes much of the high recording bitrates of their cameras and the resultant picture quality benefits, yet the BD recorder department - whilst highlighting AVCHD camcorder functionality of the machines - sets a maximum bitrate that's a wide notch below that of their consumer camcorders (and their still cameras in video mode), and a 'standard' MPEG4 highest quality mode (HG) that's further still down the bitrate ladder.

When I have an opportunity, I'll take an AVCHD-BDR into an AV shop and see whether I can test replay compatibility on Blu-ray players from the major makers, then report findings.

ClassicalMan

 

[ClassicalMan]

I was able to try out an AVCHD-BDR disc in a number of Blu-ray players in an AV shop today. The sample AVCHD-BDR had been burned using my DMR-BWT700 and the AVCHD files were shot on a Panasonic X900 camcorder in 17Mbps mode (1080/50i).

Nothing approaching scientific method was possible since only certain machines were connected up to screens, but here are the results, in case anyone else finds themselves in a similar situation:

1. All Blu-ray players that I tried from Sony, Panasonic and Samsung played the AVCHD-BDR without problem (i.e. smooth playback, scan, chapter skip, disc menu with titles etc). Machines from other makers were not connected so I couldn't try the likes of LG, Toshiba etc.

2. However, the lower-end Panasonic players (£100 or less) produced an initial menu screen that suggested the machine would not play back the AVCHD-BDR. It was only after navigating through a couple more menus from that initial menu (none of these were at all intuitive) that I could access the contents of the AVCHD-BDR. Panasonic players from about £180 upwards recognised the AVCHD-BDR right away and brought up the disc's own menu.

3. Sony players of all types (budget and more expensive machines) recognised the AVCHD-BDR immediately and brought up an option to show the disc's menu.

I downloaded the manuals for a couple of lower-end Panasonic Blu-ray players and these would imply that the machines would play AVCHD-DVDRs but not AVCHD-BDRs. However (as noted above), this was not the case, but accessing the AVCHD-BDR required some heavy lifting on these machines (after which disc playback was fine). By contrast, I noted that the cheapest Sony machine of all sported an 'AVCHD' sticker along with the customary ones trumpeting web functionality et al. So it appears that Sony make more of the AVCHD playback capabilities of their Blu-ray players than do Panasonic.

I should stress that this test was far from exhaustive and anyone interested in AVCHD-BDR playback on standard Blu-ray players should try to test any machine in advance. In my case I was looking for a Blu-ray player for a relative and, given that ease of use (with AVCHD-BDRs) was a essential, I bought a Sony.

ClassicalMan