[mythtv] FFmpeg sync

John P Poet jppoet at gmail.com
Wed Sep 17 16:48:31 UTC 2008

On Mon, Sep 15, 2008 at 6:45 PM, Janne Grunau <janne-mythtv at grunau.be> wrote:
> Hi,
> It's FFmpeg sync time. I made patches and my git mirror[1] of mythtv's
> svn repository available to testers in the #mythtv irc channel on
> freenode.
> I think the sync is pretty stable and I'm only aware of
> one "regression". The volume of FFmpeg's native AC3 decoder after
> downmixing 5.1 audio to stereo. I've compared the implementation with
> the specs and I'm pretty sure that the implemantion is correct.
> Previously we amplified the audio during downmixing but I don't think it
> belongs there. It looks as if the code correct and more importly the
> AC3 can use now a SIMD implemation of the downmixing function.
> So I'm writing a software amplifier in mythtv instead. I initially will
> use it only for downmixed AC3 audio but it also be used for extended
> volume control. I hope to have that ready in the next few days.
> AC3 passthrough with the native decoder was changed and is afaik
> untested.
> The FFmpeg devs have just increased the major libavcodec version and are
> currently dropping deprecated parts. Some of them (software scaler and
> colorspace converted, ...) are used by mythtv.
> The most important changes for mythtv in FFmpeg are E-AC3 decoder, H264
> decoding fixes, and native AAC decoder. The AAC decoder misses features
> to make libfaad obsolete though.
> http://www.grunau.be/mythtv_ffmpeg_sync_15219_18295.diff.bz2
> the patch has to applied with "patch -p1" to a complete trunk checkout
> since it needs modify some plugins too.
> Alternatively the branch ffmpeg/latest of my git tree could be used.
> I plan to apply soon if no regressions are reported and someone verifies
> that AC3 passthrough still works.
> Janne
> [1] git clone git://git.jannau.net/mythtv.git, only trunk and 0.21 fixes
> are tracked

Hi Janne,

I installed this patch last night.  Tried watching about a dozen
different shows, all with AC3.  Some where ATSC OTA, and some where
from the HD-PVR.  I had zero problems.  S/PDIF pass-through worked
fine, as well as timestretch.

A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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