iPhone Web应用程序：HTML5数据库和音频文件

Question

I'm having issues with audio files on the iPhone web-app. Seems as each time an audio file is played, it's loaded first then played, even if repeating the same audio on a page that hasn't refreshed (done via javascript). From what I've research manifest files would be great but they are for offline application. I'm now researching HTML5 databases.

Does anyone know if HTML5 databases can store audio files such as mp3? The end result it then to pull the mp3 from the database. It might still have to load the file each time from the database but I'm hoping it's quicker than retrieving it from a server.

Thank you.

Answer 1

I think what you are after is possible , however you have a significant hurdle in that the implementation of HTML5 databases on most browsers is limited to 5mb as per w3c recommendations:

A mostly arbitrary limit of five megabytes per origin is recommended.

Having said that the way its implemented in iPhone Safari is that databases can grow until they reach 5MB in size at which point the browser will ask the user if they wish to allow for the extra size, asking again at 10, 50, 100 and 500MB (see section "Estimated Database Size" in this post by html5doctor ).

There is no limit on the number of databases you can build per domain in safari, however according to this post by Cantina Consulting you can have a total of 50MB across all databases in a single domain .

Given these parameters, a possible work-around for this implementation is to split your mp3 blobs across multiple databases , creating a new database each time your reach 4.9MB, however even if you follow this design it may not be ideal as you will still experience the following:

• 50MB is not a lot of audio files, a typical 5/6min song is about 5MB at 128Khz, so that only gives you space for about 1CD (60 min) of mp3 songs, after this you will need user cooperation to use additional database space.
• You will still have significant security issues trying to play the mp3 blobs from the javascript runtime, it may be possible to bypass these tricking flash into thinking they are mp3 stream but I'm not sure how you'd go about it.

Feel free to have a play around with this iPhone HTML5 SQL Client I put together, you may want to use something similar for experimenting with your local mp3 Database.