[FFmpeg-soc] extension of ac3 parser

[Bartlomiej Wolowiec]

On poniedziałek, 21 kwietnia 2008, Michael Niedermayer wrote:
> On Mon, Apr 21, 2008 at 12:49:41AM +0200, Bartlomiej Wolowiec wrote:
> > On niedziela, 20 kwietnia 2008, Michael Niedermayer wrote:
> > > > Index: libavcodec/ac3_parser.h
> > > > ===================================================================
> > > > --- libavcodec/ac3_parser.h	(wersja 12910)
> > > > +++ libavcodec/ac3_parser.h	(kopia robocza)
> > > > @@ -35,14 +35,15 @@
> > > >
> > > >  /**
> > > >   * Parses AC-3 frame header.
> > > > - * Parses the header up to the lfeon element, which is the first 52
> > > > or 54 bits - * depending on the audio coding mode.
> > > > + * Parses the header up to the lfeon element, which is the first 52,
> > > > 54, or 104 bits + * depending on the audio coding mode and
> > > > read_channel_map. * @param buf[in] Array containing the first 7 bytes
> > > > of the frame.
> > >
> > >                                                 ^^^^^^^
> > >
> > > 7 bytes and 104 bits ?
> > >
> > > >   * @param hdr[out] Pointer to struct where header info is written.
> > > >
> > > > + * @param read_channel_map[in] Determines whether channel_map is to
> > > > be set
> > >
> > > why is this conditional and not always done?
> > >
> > > [...]
> >
> > Because  e.g. while parsing in buffer there are just 8 bytes, which won't
> > be enough to read full information. According to solution proposed by
> > you, parser firstly reads 7-byte headers, then, when full set of frames
> > is in buffer, it sets number of channels etc.
>
> Well in that case i think it might be better to have these in seperate
> functions.
>
> That is we need the following patches (if you agree and theres no issue iam
> missing)
> * change ff_ac3_parse_header() to take a GetBitContext instead of const
> char * * add a ff_ac3_parse_header_full() which calls ff_ac3_parse_header()
> and then reads the channel_map stuff.

Ok, the only case which is questionable in my opinion, it's using it in ac3 
decoder. Should before call ff_ac3_parse_header() new GetBitContext be 
created, so that the old one won't be changed? (decoder must also read mix 
levels)

-- 
Bartlomiej Wolowiec