With HCCB (High Capacity Color Barcode) of which an implementation is Microsoft Tag you can get 1.5 MB with 600dpi color on a A4. If you add the best compression techniques (ppmd) depending on the source material you could get 8 times as much english text, easily fitting the pearls or religion: Tenach, New Testament, Quran, Mahabarata, The Dhamapada, the Atthakavagga and the Parayanavagga, Rhinoceros and Lotus Sutra, The Book of the Dead and the Sri Guru Granth Sahib and explanatory texts and commentary on one single A4.
Or you could get 4 minutes of stereo music, Opus @40Kbps or half an hour of speech Opus @6Kbps - (Vinyl LP seems to be more efficient and simpler for that). Codec2 gets even more efficient at 600bps.
Or the best 25 classical pieces in MIDI, for example Beethoven Symphony #5 in C minor is a 322 KB midi file (compressed 60 KB). With compressed ABC or Alda notation you could even fit 10 times as much. Or you can just read the ABC and automatically ‘hear’ the music in your head.
Even so perhaps a better and more cost effective system is microfilm, here an example of the bible printed on a 2 inch film: http://www.amazon.com/Microform-Bible-Much-Like-First/dp/B00…
For this you don’t need a computer, just a lensing system. It has one downside, the blind cannot use this unless you'd make an OCR to TTS or braille display converter on top of it. Same goes for printing text out with really small letters ay 1200 dpi.
Or as described in the book Mindhacker you could use Dutton Speedwords/Briefscript word abbreviations preferrable tailored to Esperanto to double the text on the microfilm or on your handwritten A4. https://github.com/leonardoce/bumot
For dance there’s “Dance Notation”, most specifically Labanotation, but there are others, such as Benesh notation.
For juggling there is SiteSwap for vanilla flavored juggling, and now it’s been extended in different directions, perhaps most completely by BeatMap.
Here’s a demo PNG file which contains 48 QR codes (6x8) at V23 level with L correction (~7% recovery). That’s 1091 bytes per code, or just over 51KB per page when printed at 300 dpi. This level of density seems to be very reliable using ambient lighting and an iPhone 5c.
One is able to read a QR code which was 66% of that size, but it required turning on the iPhone’s flash in order to be reliably read. That level of density would allow fitting 9x12 codes on a single page at 300 dpi, which would yield 115KB of data per page.
When trying 600 dpi, at 1 dot per pixel the codes were totally unreadable by a cell phone. The above 115KB/page density is the equivalent of 4 dots per pixel at 600 dpi. The good news is this means the system doesn't require a 600 dpi printer. In fact, at 1 dot per pixel, the 51KB/page density is equivalent to 100dpi, and the 115KB/page density is equivalent to 150dpi.
the 51KB/page PNG file: QR playground