szuvbo:

Mam problem z winampem


!!! 3 Plikach mp3 kodowanych zmiennym bitratem (niezaleznie jakim) nie mozna przeskoczyc w kawałku do jakiegoś fragmentu np o 2 minuty.
Powoduje to ponowne uruchomienie danego kawałka od początku pomimo źe zegar pokazuje własnie te 2 minuty ?????????

PORADZCIE COS !!!!

The reason for programs like Winamp and Mp3/Tag Studio displaying the wrong information for some VBR–mp3:s (the ones without valid VBR–headers) lies in the nature of mp3–encoding and the relation between frame–size and bitrate. (look at the bottom of this page if you're only interested in how to fix this problem)

An mp3 file is made out of thousands of so called "frames" in which the sound data is stored. A frame always contains a constant amount (time) of sound. Each frame is encoded with a certain bitrate, the higher the bitrate the lower the compression of the sound (and hence better sound), but of course when the compression is lower the size also gets bigger.

A normal mp3 file has the same bitrate for all it's frames, so you just have to look at the first frame in the file to be able to tell how many frames a file contains (and hence what its playlength is) with a simple division. You can also calculate the position of any given playtime in the file by a simple multiplication.

But in the case of VBR the frames in the file are all encoded with different bitrates (depending on the complexity of the sound in each frame). This has several disadvantages though:

1. You cannot calculate the playlength of a file without traversing all its frames. This operation is too time consuming during normal execution, and therefore the exact number of frames in the file is stored in the VBR header instead, so the playlength still can be calculated with a simple multiplication. BUT, if the file has no VBR header it is assumed that all the frames have the same bitrate as the first frame in the file, and the calculated playlength will be completely wrong.

2. You can't seek directly to any certain playtime, since you don't know the size of the frames before that point of time. Therefore you must traverse every frame up to that point to get it right. This operation is too time consuming during normal execution, and therefore there is a lookup table for the file offsets of 100 different point of time in the VBR header. Interpolation between these gives a good enough result when seeking in the file. BUT, if the file has no VBR header it is assumed that all the frames have the same bitrate as the first frame in the file, and the calculated jump offsets will be completely wrong.

Anyway, luckily all these problems are easily fixed by adding new VBR–headers to your VBR files with Mp3/Tag Studio. This is easily done with the repair tool.