[FFmpeg-devel] [PATCH] aacenc: Fix issues with huge values of bit_rate.

[Reimar Döffinger]

On Sat, Apr 07, 2012 at 12:34:24AM +0200, Michael Niedermayer wrote:
> On Fri, Apr 06, 2012 at 03:58:19PM +0200, Reimar Döffinger wrote:
> > Do not pointlessly call ff_alloc_packet2 multiple times,
> > and fix an infinite loop by clamping the maximum
> > number of bits to target in the algorithm that does
> > not use lambda.
> > 
> > Signed-off-by: Reimar Döffinger <Reimar.Doeffinger at gmx.de>
> > ---
> >  libavcodec/aaccoder.c       |    3 +++
> >  libavcodec/aacenc.c         |    4 ++--
> >  tests/ref/acodec/aac        |    4 ++++
> >  tests/ref/acodec/dca        |    4 ++++
> >  tests/ref/acodec/nellymoser |    4 ++++
> >  tests/ref/acodec/ra144      |    4 ++++
> >  6 files changed, 21 insertions(+), 2 deletions(-)
> >  create mode 100644 tests/ref/acodec/aac
> >  create mode 100644 tests/ref/acodec/dca
> >  create mode 100644 tests/ref/acodec/nellymoser
> >  create mode 100644 tests/ref/acodec/ra144
> > 
> > diff --git a/libavcodec/aaccoder.c b/libavcodec/aaccoder.c
> > index 25187b7..b6fefd3 100644
> > --- a/libavcodec/aaccoder.c
> > +++ b/libavcodec/aaccoder.c
> > @@ -721,6 +721,9 @@ static void search_for_quantizers_twoloop(AVCodecContext *avctx,
> >      int allz = 0;
> >      float minthr = INFINITY;
> >  
> > +    // for values above this the decoder might end up in an endless loop
> > +    // due to always having more bits than what can be encoded.
> > +    destbits = FFMIN(destbits, 5800);
> >      //XXX: some heuristic to determine initial quantizers will reduce search time
> >      //determine zero bands and upper limits
> >      for (w = 0; w < sce->ics.num_windows; w += sce->ics.group_len[w]) {
> 
> not really pretty but should be ok if the value is sufficient

Sufficient in which way?
The absolute limit for this value that is checked in aac_encode_init is
6144 anyway, and all this code does is limit the maximum bitrate to
about 255 kbit/channel which should be more that enough even if a bit
below the theoretical maximum for AAC.
As to whether it is low enough I am not as sure since the overhead
is not trivial to calculate, so I basically just tested that 5815
was enough for my samples to work and gave it a few bits headroom
just to be sure.