Change how we handle RA units

[justinruggles]

What we do now:

1. Set RA unit size to near 10 seconds, with each frame based on original avctx->frame_size.
2. Multiply avctx->frame_size by RA unit size.

What we need to do:

• Allow user to set RA unit size through avctx->gop_size.
• Buffer frames internally until we have an RA unit or end-of-stream.
• If current call to encode_frame() will return the encoded RA unit, set avctx->coded_frame->pts and return encoded RA unit size in bytes.
• If current call to encode_frame() only adds to the buffer, leave avctx->coded_frame->pts as-is and return 0.

[thiloborgmann]

Almost done. Two questions left:

1. In encode_ra_unit():
   is "unsigned int" enough to hold the number of encoded bytes of the ra-unit?
2. PTS most likely not set correctly. I just used #frame and I have not crosschecked with other encoders yet.

[thiloborgmann]

"2". => I crosschecked with vorbis and assign the total number of samples now. ffmpeg also shows a reasonable "time" output like vorbis/flac now - although they differ for +/- 0.02 seconds...