4096 bytes while the packet can be up to 18726 bytes.
The code also keeps decoding until all input data has been used up,
not respecting AVCODEC_MAX_AUDIO_FRAME_SIZE.

The patch increases the buffer size and return after decoding one frame.
Also fixes dts_decode_init to return -1, not 1, on failure.

Patch by Uoti Urpala  ||| uoti : urpala |!| pp1 : inet : fi |||

Originally committed as revision 5307 to svn://svn.ffmpeg.org/ffmpeg/trunk