View Full Version : AVCHD System Bit Rate
August 6th, 2011, 03:53 PM
This is an old question that has generated a lot of discussion in a lot of forums, apparently, but even so I still can't seem to find _the_ definitive answer (e.g., referencing the formal standard). The AVCHD Format Specification Overview at AVCHD INFORMATION WEB SITE (http://www.avchd-info.org) lists a System Bit Rate of "<= 24Mbps (<= 18Mbps for DVD)" in one chart and "<= 28Mbps" in the following chart, the latter for the newer 2.0 version of the standard (announced July 1, 2011). What, exactly, is the "System Bit Rate"? Is it the average bit rate, maximum peak "instantaneous" (per frame) bit rate, maximum bit rate into the buffer of the player, or...what?
Practically speaking, if I am authoring an AVCHD compliant red-laser disc on DVD-R or DVD+R, what values for maximum, minimum and average bit rates should I select for the maximum encoding quality that is compatible with the maximum number of BD player models (including the PS3)? Second question: What bit rate parameters can I get away with on many (but not all) players? Third question: What are the highest bit rates that _some_ players allow?
PS. I am not taking about BDMV on red-laser discs (BD-5/BD-9). I am led to understand that many players including the PS3 won't play these, at least not on recordable media, although I have also heard that there may be a workaround that works for some players (including the PS3).
August 6th, 2011, 06:11 PM
I can answer your question for PS3 from extreme experience. Any bit rate over 24-28, PS 3 will not read.
PS 3 will read 17 Mps w/o problems. This is for AVCHD> DVD-R's being used via RED LASER.
August 7th, 2011, 01:15 PM
All bitrates are compatible if you put the MTS files on a flash drive or HDD and then transfer the file to the PS3. You can also read off of Memory Sticks and SD cards at full bitrate. 1080p60 files require all the video post-processing to be turned off and do not have audio.
August 8th, 2011, 12:12 AM
The 28Mbit/sec figure is only for 1080/50p and is a new standard. This means it will only be guaranteed to work on equipment saying it supports AVCHD 2.0, that equipment doesn't exist yet.
When putting AVCHD on DVD for playback on Blu-ray players there is the physical issue that a DVD can only be read fast enough to guarantee 18Mbits/sec or less, hence the slower figure for DVD. When AVCHD is not used to create a DVD disc, i.e. you are using it on hard-disc/memory cards/or a real Blu-ray disc, you can go as high as 24Mbits/sec. In practice you can go higher than 24Mbits/sec, but it isn't classed as AVCHD at that point.
August 8th, 2011, 09:57 AM
When putting AVCHD on DVD for playback on Blu-ray players there is the physical issue that a DVD can only be read fast enough to guarantee 18Mbits/sec or less, hence the slower figure for DVD.Yes, I realize why the lower number exists but I want to know what the number actually and specifically represents, and also in a practical sense what numbers and parameters to set in an H.264 encoder (see my original post). Part of this is learning what specific numbers some (but not all) players can handle in actuality (as opposed to what the spec guarantees they can handle). I am led to believe that at least a few current BD players _do_ play AVCHD higher than 18Mbps from a DVD (up to 24Mbps, I have heard). Those players aren't officially AVCHD 2.0 compliant because they were released prior to the new spec but perhaps they would pass compliance tests under the new standard.
August 8th, 2011, 10:59 AM
Yes, I realize why the lower number exists but I want to know what the number actually and specifically represents, and also in a practical sense what numbers and parameters to set in an H.264 encoder (see my original post).
The numbers represents the maximum bit-rates to comply with AVCHD and have it play on equipment that complies with AVCHD and be almost 100% certain it will play. If you use higher bit-rates then it might work, it might not, you can of course do anything you want and try higher bit-rates. The DVD Video spec states players should read at x2 speed, this is around 21Mbits/sec and gives time for error correction and other overheads. So for HD on DVD, it is assumed x2 speed is all you have, so when you take 18Mbits/sec for the video and factor in audio and other overheads you are right at the limit already but with little ability for error correction as the drive can't afford to miss anything as you get a buffer underflow. This is why 24Mbit/sec is excluded from DVD media under the AVCHD spec as DVDs in Blu-ray players can only be assumed to be reading at 2 speed maximum.
. Part of this is learning what specific numbers some (but not all) players can handle in actuality (as opposed to what the spec guarantees they can handle).
There is no one answer to what they will handle above the spec as they will all vary, the only way to know for sure what maximums is if you know the reading speed for DVD in that player. Not only that the type of video it is, the quality of the blank media, and the H264 encoder you use can all make a difference as to how well it will handle being pushed to higher data-rates. A test disc might work fine at a higher rate just to find on different footage it crashes and burns due to a complex scene causing a sustained maximum bit-rate.
In terms of Blu-ray players themselves and their decoder, they should have no issue with video bit-rates upto 40Mbit/sec which is the Blu-ray spec, but as above you can't get a DVD to spin anywhere near fast enough in most players for that, hence the much lower maximums. Think of AVCHD as Blu-ray lite and that it allows the ability to create a "poor mans" Blu-ray disc by burning HD to a DVD disc, with the caveat you have to use much lower bit-rates.
Those players aren't officially AVCHD 2.0 compliant because they were released prior to the new spec but perhaps they would pass compliance tests under the new standard.
I doubt there are any existing players players that will be AVCHD 2.0 compliant simply because it requires decoding H264 at Level 4.2. All current hardware tops out at Level 4.1 which is all that has been required up to very recently. Hardware reported to play AVCHD 2.0 files from camcorders at up to 28Mbits/sec are doing so by downgrading the output, either to half the frame rate or interlacing it, which defeats the object of full progressive HD at 50/60 frame rates.
Hope that helps.