[mythtv] DD5.1 passthrough disabled by timestretch?

[John P Poet]

On Mon, Jul 26, 2010 at 4:17 AM, Jean-Yves Avenard <jyavenard at gmail.com> wrote:
> Hi
>
> On 26 July 2010 01:26, John P Poet <jppoet at gmail.com> wrote:
>> I just upgraded to the latest trunk for the first time since r24684.
>> Enabling timestretch seems to turn off DD5.1 passthrough -- preamp
>> reports Prologic instead of Dolby Digital as soon as I enable
>> timestretch.  Toggling timestretch off does not return it to DD5.1,
>> either.  I do not have "Upconvert stereo to 5.1 surround" enabled
>> because I want my preamp to handle that conversion.
>>
>> Is this a known issue, or should I create a ticket for it?
>
> Is your source stereo or multi-channel?
>
> If stereo, this is normal. You just can't do passthrough with
> timestretch enabled. Audio will have to be decoded, stretched.
> And for stereo content or if the hardware supports natively the
> requested number of channels, it won't be re-encoded as it only add
> delays and loss of quality.
>
> So:
> Stereo AC3 -> decoded -> timestrech -> stereo PCM
>
> If using SPDIF or user didn't check the "support multi-PCM option":
> 5.1 AC3 -> decoded -> timestretch -> re-encoded in AC3


I am using S/PDIF.  The source material is either from ATSC MPEG2 with
DD5.1, or HD-PVR H.264 with DD5.1.

I will have to look for this "support multi-PCM option" option.  It
must not have been available at r24684, since this all worked fine
until upgrading to trunk this past weekend.  So, turning on "support
multi-PCM option" should re-enable:

5.1 -> decode -> timestretch -> re-encode 5.1 ?


> If using a medium supporting natively the requested amount of channels
> (e.g. analog audio or HDMI or anything with the "multi-channels PCM"
> settings activated, the decoded audio data is sent as-is.
>
> Once you activate timestretch, it's activated forever. When you
> toggled it off, it is still activated, just with the stretch value of
> 1.0. That's how AVFD works, we didn't changed anything there. Not sure
> why this was done like this to start with. There's no real
> requirements anymore to do it that way, we could completely disable
> timestretch instead


My memory, is that it was done that way so turning timestretch on/off
would be seemless, instead of having a brief pause during playback.


Thanks JY,


John
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