[mythtv] [mythtv-commits] Ticket #6569: ac3 level is low for 5.1 source

[Mark Spieth]

>Comment(by danielk):
>
> Mark, have you tried submitting this to the ffmpeg folks?

no. the matrix is incomplete anyhow.

I was watching F1 last night on onehd and it worked well up to a point and 
then it reverted to 5.1 soft (-10dB) and 2.0 normal.
not sure why yet as it shouldnt have happened.

>A hardcoded gain increase can result in clipping and is not an appropriate
> way to address the "loud commercials" problem.  This problem varies across
> different broadcasters/affiliates and really must be fixed at the source.
> This patch would cause problems on channels that do set proper levels, as
> well as on other ac3-bearing content, such as DVDs.
>Additional reading: http://www.tvtechnology.com/article/12644

yes I agree.
however across all of our HD channels doing 5.1, there was no difference in 
level.
also a solution is better than none however bad it may be.

we need some more stats for this from more sources to see how this tracks, 
and whether there are any exceptions.
perhaps there is special processing done for 5.1 in the decoder that does 
not get enabled in the 2.0 case which causes this.

I have seen posts which provide a patch for a52 ac3 decoder, but I suspect 
doesnt fix this in this way either.
So I know others are seeing this as well.

there is also a 2nd problem which Im testing where, if you are in 6ch mode, 
and ac3 2.0 switches, the audio out gos to 2ch mode and never goes back to 
6ch mode and you loose the true 6ch mode when 5.1 is restored. all audio is 
then via upmixed functionality. havent tested this patch yet.

cheers
mark