`Info` header is used for CBR files, but in some cases not **every**
frame in these files is the same size. This change stops using the
single frame after the `Info` frame as the 'template' (and assuming all
subsequent frames are the same size/bitrate), and instead derives the
bitrate from fields in the `Info` header. This works for files which are
'almost' constant bitrate, like the one in Issue: androidx/media#1376 where every
frame is either 1044 or 1045 bytes except the one immediately after the
`Info` frame which is 104 bytes (32kbps), resulting in a wildly
incorrect duration calculation.
PiperOrigin-RevId: 636151605
5b3066f380