If you wanted to compress a movie (say a DVD) down to fit on a CD and use modern compression schemes; yes AVC (via the X264 codec) and AAC for the audio…what sort of length movie could you use and still get good results?
Assume
- 1 CD is 700 MB
- The AAC audio is 128 kbps (average bit rate)
Knowing the target file size and movie length, it’s possible to work out the required target bit rate of the video stream to fill the 700 MB CD. Here’s the required bitrate as a function of movie length:
1 hour movie need to set it at 1501 kbps
1.5 hour 957
2 hour 685
The bit rate is a good indicator of quality too. So a 1 hour movie would be great quality, 90 mins very good indeed, but by 2 hours you would probably see some artefacts.
Note: the above calculations do take into account the audio track and the (small) overhead of the mp4 or mkv container.
The above quality is only based on the data rate. Another factor is the trade-off between compression time and quality; they are almost in a linear relationship. For the 2 hour one you could use one of the ‘1 Pass’ profiles and get the movie to fit on the CD and take only about 2.5 hours to do so, but the quality could be a wee bit dodgy.
You could increase this quality by using one of the ’slower’ (HQ or CE) encoding profiles as per my other posts. I’d suggest if you left it running over night, you could compress down a 2 hour film at that data rate (685) and get quite good quality. Would be interesting to try.
One of the benefits of AVC is the ability to adapt the compression to suit the target device or quality. So you can use a very high quality set of settings and take 19 hours to compress a 2 hour movie. By the way even these are not the highest quality (read: slowest) settings.
The good people over at the doom9 forum have already created a number of Profiles which you load into MeGUI and then choose from a drop down list. They range from the above multi-pass through to ” I just need an okay compression” quick single pass.
Even within such single passes they offer at least 3 profiles, balancing speed of encoding against quality:
1P-Maxspeed: Everything disabled for max encoding speed (good for live capturing).
1P-Intermediate: Intermediate settings for average speed and final quality.
1P-Goodquality: Settings for good quality with 1 pass.
(Source: above doom9 forum post)
You can also use these as a basis and create your own profiles too.
I did a quick series of tests on a 2 minute DVD sample (video only) to confirm these three – unchanged from defaults – work as designed :
- 1P-Maxspeed: About 2 mins
- 1P-Intermediate: About 5 mins
- 1P-Goodquality: About 8.5 mins
On balance, I’d be aiming for 1P-Intermediate. If it’s a show that has little or no movement – say, a chat or comedy show – I’d probably copy that profile and drop the data rate to say 700kpbs from the default of 1000.
Using MeGUI I took just over 1 hour of DVD and compressed it down via the ’state of the art’ compression schemes:
- Video AVC (aka H.264 or MPEG4 Part 10) using the CE_Highprofile at 1000 kbps
- Audio AAC using the FAAC 128 kbps ABR profile
The 1 hour, 5minute movie took over 5 hours to compress on a Pentium 4 3 GHz. This VOB had already been decrypted; so add another 15 mins for that step. Here’s the breakdown of the MeGUI timings:
- Indexing the VOB to make a D2V file: 2 mins
- AAC audio: 8 mins
- AVC pass 1 of 2: 1 hour 10 mins
- AVC pass 2 of 2: 4 hours 5 mins
- Muxing of AAC and AVC to final MP4 file: 3 mins
A great thing about MeGUI is that all of the above is done without user interaction; via the One Click Encoding option. Pass 1 reported 23 fps, Pass 2 reported 6.7 fps
Quality looks excellent on final mp4 file. It started at noon and was done just after 5:25 pm.
Size comparison for this 1 hour 5 minute movie:
- Original decrypted VOB is: 3.92 GB
- Final mp4 is: 534 MB
But, to be fair, VOB has multiple soundtracks. Also this is an old black and white movie. Will try colour when I have another 5 hours to spare 
In trying to get a $10 adapter cable to work on the laptop, I hit a rare Linux bug. And the system, she go booom. Wouldn’t boot in normal mode, nor in recovery mode. Same ’small’ problem; pretty much couldn’t find the hard drive.
It was nothing to do with the cable per se.
Actually it was, bizzarely, claiming it couldn’t find Mimix. Which is a totally different operating system! I knew the (one and only) disk was there okay as it was a dual boot and Windows XP was fine. So it had to be something else.
Turns out “In the fstype tool there is a problem if the lower 16 bit of number of free inodes in a ext3 filesystem happens to match minix filesystem magic.
This will cause the system not to boot since ubuntu will attempt to mount the filesystem as a minix filesystem.”
http://www.ubuntuforums.org/archive/…p/t-95729.html
I got around it via these steps (safely recorded here – and elsewhere – if it happens again):
- Boot a Live CD of Ubuntu (5.1 ok)
- set root password (sudo passwd root)
- mount /dev/hda1 as /root
- cd /root then cd to (say) /tmp dir
- create a junk.txt and put some data in it
- save it, shutdown Ubuntu, remove live cd and reboot
And it worked.
