When creating music files for online delivery using Flash (such as through our range of playheads) it's important to make sure the files are encoded properly. Flash player claims to support MP3 files without giving details, but there are some formats and bitrates it has problems with.
Files encoded using 'standard' MP3 format at CONSTANT bit rate will normally play, provided the sample rate is a multiple of 44.1kHz - other 'interpolating' sample rates cause Flash Player to speed up the playback. Sample rates of 96000, 44100, 22050 and 11025 samples/second at 8, 16 and 32 bit depth will all work fine.
The following formats are suggested for web downloading:-
| Samples Hz | Bit depth | Bitrate kbps | Ideal for |
|---|---|---|---|
| 44100 | 16 | 128 | Music over broadband |
| 22050 | 16 | 56 | Speech/music over dialup |
| 11025 | 8 | 24 | Speech over dialup (phone quality) |
Encoding MP3s in VARIABLE BIT RATE will always lead to problems. Flash Player cannot stream VBR files properly, and will either completely ignore them or play back silence. The player also has serious problems with 'fake MP3s' - files wrapped in an MP3 container but with the audio data encoded by some non-standard system. Some audio codecs produced by Microsoft allow the creation of an MP3 with Microsoft's own ACM audio compression, and Flash Player falls over laughing at those.
Files encoded at interpolated sample rates (such as 32000, 8000, 64000) will play, but at the incorrect speed. Bit depth and bitrate have no effect on this issue, which is a core limitation of the Flash Player audio decoder and is not specific to our software.
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