LDImage
From DaphneWiki
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(→Why 44100 Hz audio instead of 48000 Hz?) |
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=== Why 44100 Hz audio instead of 48000 Hz? === | === Why 44100 Hz audio instead of 48000 Hz? === | ||
| - | Daphne is already built on 44100 Hz audio, and changing Daphne to use 48000 Hz audio would require changing all | + | Daphne is already built on 44100 Hz audio, and changing Daphne to use 48000 Hz audio would require either changing all existing .OGG audio files that are out there (not worth it), or supporting both 48kHz and 44.1kHz (which I don't have a good enough reason to consider at this point). I feel that 48 kHz audio is a good conservative choice for preservation, but for presentation, 44.1 kHz audio should be more than adequate, and it reduces the overall file size (which is important to me). |
Revision as of 17:09, 7 October 2008
Laserdisc Image Format
The laserdisc image format will use the container format I've written for mpolib (not discussed here).
| Blob Index | Description |
| 0 | the header, which needs to contain at minimum a version identifier. At this time, the only thing it will contain will be the four ASCII bytes '1', 'L', 'D', 'I' in that order. |
| 1 | a common JPEG header (ie the 'tables') |
| 2 | an "abbreviated" JPEG of field 0 of track 0 |
| 3 | uncompressed 44100 Hz 16-bit PCM audio spanning the time occupied by field 0 of track 0 |
| 4 | an "abbreviated" JPEG of field 1 of track 0 |
| 5 | uncompressed 44100 Hz 16-bit PCM audio spanning the time occupied by field 1 of track 0. |
| 6 | an "abbreviated" JPEG of field 0 of track 1 |
| ... | And so on until the final laserdisc track has been stored |
| Last Blob | the VBI data (stored in my VBI format) |
So the algorithm to search for a track will be:
blob index = (track index * 4) + 2
Because there are 2 blobs at the beginning.
Why does the VBI blob need to come last?
This is actually kind of important. The VBI is the data that I feel is most likely to change if anything changes, and by putting it at the end, it ensures that any required changes to the VBI will have a minimal effect on the overall image file. If the VBI was at the beginning and its size needed to be changed, this would impact the entire file which would be costly.
Why 44100 Hz audio instead of 48000 Hz?
Daphne is already built on 44100 Hz audio, and changing Daphne to use 48000 Hz audio would require either changing all existing .OGG audio files that are out there (not worth it), or supporting both 48kHz and 44.1kHz (which I don't have a good enough reason to consider at this point). I feel that 48 kHz audio is a good conservative choice for preservation, but for presentation, 44.1 kHz audio should be more than adequate, and it reduces the overall file size (which is important to me).
