[Mplayer-dev-eng] AC3 output.

[Arpi]

Hi,

> > 	Finally I make AC3 output works under SBLive in SMP, so I'm
> > continuing/starting with the AC3 output support in mplayer (maybe later
> > continue with IFO/RawDVD support :-). Anybody working on it right now?
Yes, Peter Niemayer <niemayer at isg.de> sent a patch, but I refused it.
You should read the list archive back to find the reasons.

In short:
- AC3 passthrough code shouldn't be in libac3.
  libac3 is a software decoder. just memcpy'ing soem buyes shouldn't be
  there.
  It should go to dec_audio.c. There is 2 coices:
   - adding to PCM codec (it already has some support)
   - adding a new codec, for example HWAC3
  A simple AC3 frame sync code can be written in 10 lines. I see no
  sense of using libac3 for this purpose.
  Btw I think that AC3 stream shouldn't be synced and hacked to work,
  it's enough to send ac3 starting code once, before the playback starts,
  and then send the ac3 stream unmodified. So no extra code required.
  (must be tested, i have no external AC3 decoder)
- sh_audio->o_bps must be fixed (must be set to compressed ac3 bytes / sec)
  to avoid A-V desync and buffer overflow.
- as you said too, a control() function should be added to ao_oss.c, to
  query/set AC3 support.
- you have to #ifdef AFMT_AC3 constant everywhere, because it isn't defined
  on non-linux systems, and in older linux kernel includes (old soundcard.h)

> 	I need to make some changes to libac3, I should use the
> QUERY_FORMAT in control() in ao_oss.c if the /dev/dsp is able to do raw
> AC3 output through SPDIF before decoding the frame, but after looking
yes, it's ok to use something like:
  audio_out->control(AOCONTROL_QUERY_FORMAT,AFMT_AC3)


A'rpi / Astral & ESP-team

--
mailto:arpi at thot.banki.hu
http://esp-team.scene.hu

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