[FFmpeg-devel] [PATCh] aac parser: Don't write channels, sample rate, and frame size each frame

[Michael Niedermayer]

On Wed, Mar 03, 2010 at 05:06:32AM -0500, Alex Converse wrote:
> On Mon, Mar 1, 2010 at 8:23 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Mon, Mar 01, 2010 at 08:16:48PM -0500, Alex Converse wrote:
> >> They are part of the invariant header and shouldn't change each frame
> >> anyway. This prevents them from overwriting information provided by
> >> backwards compatible extensions.
> >
> > what you attached does not match the description
> >
> > besides "shouldn't change" gives me a strange feeling ...
> > if we can support it changing it would be a nice "wish/feature request"
> >
> 
> This patch appears to be necessary for either the put a hack in
> av_find_stream_info() or fix all the demuxers approach to handling
> backwards compatible SBR. It breaks nothing we already support as far
> as I can tell.
> 
> Based on that should we move forward with it, make some changes to it,
> or try to move to a new approach?
> 
> [patch re-attched]
> 
> --Alex

>  aac_ac3_parser.c |   10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 074f9a540038b4836308ca477b806204f56c6229  aac_parser_extensions.diff
> diff --git a/libavcodec/aac_ac3_parser.c b/libavcodec/aac_ac3_parser.c
> index 85993c0..23a1d0a 100644
> --- a/libavcodec/aac_ac3_parser.c
> +++ b/libavcodec/aac_ac3_parser.c
> @@ -71,10 +71,12 @@ get_next:
>      *poutbuf_size = buf_size;
>  
>      /* update codec info */
> -    avctx->sample_rate = s->sample_rate;
>      if(s->codec_id)
>          avctx->codec_id = s->codec_id;
>  
> +    if (avctx->codec_id != CODEC_ID_AAC) {
> +        avctx->sample_rate = s->sample_rate;
> +

this one needs a comment, its likely not obvious for the causual reader why
this is not done for aac


>      /* allow downmixing to stereo (or mono for AC-3) */
>      if(avctx->request_channels > 0 &&
>              avctx->request_channels < s->channels &&
> @@ -83,12 +85,14 @@ get_next:
>              (avctx->codec_id == CODEC_ID_AC3 ||
>               avctx->codec_id == CODEC_ID_EAC3)))) {
>          avctx->channels = avctx->request_channels;
> -    } else if (avctx->codec_id != CODEC_ID_AAC || s->channels) {
> +    } else {
>          avctx->channels = s->channels;
>          avctx->channel_layout = s->channel_layout;
>      }
> -    avctx->bit_rate = s->bit_rate;
>      avctx->frame_size = s->samples;
> +    }

id guess this could benefit from a comment as well


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Incandescent light bulbs waste a lot of energy as heat so the EU forbids them.
Their replacement, compact fluorescent lamps, much more expensive, dont fit in
many old lamps, flicker, contain toxic mercury, produce a fraction of the light
that is claimed and in a unnatural spectrum rendering colors different than
in natural light. Ah and we now need to turn the heaters up more in winter to
compensate the lower wasted heat. Who wins? Not the environment, thats for sure
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