Opened 11 years ago

Closed 11 years ago

#8627 closed defect (fixed)

Upmix not working - got weird sound on DVB channels that transmit only 2 channels (Stereo)

Reported by: benny@… Owned by: JYA
Priority: major Milestone: unknown
Component: MythTV - Audio Output Version: Unspecified
Severity: medium Keywords:
Cc: Ticket locked: no


Testing trunk-25198 with MythBuntu? weekly builds (0.24.0~trunk25198-0ubuntu0~mythbuntu1)

  • Audio Configuration:
    • Device set to: ALSA:iec958
    • Speaker configuraation: 5.1
    • DTS and Dolby Digital is checked
    • The computer is connected directly to a Harmon Kardoon receiver via Digital Coaxial cable.
    • Upmix is on - set to "Fastest"

When looking on DVB channels that transmits only 2 channels, the receiver detect Dolby Digital audio but, the upmix results in just hearing a lot of garbage.

DVB channels that transmits more then 2 channels, already 5.1 or something similar, then everything works OK.

Turning off upmix in configuration results that all DVB channels are transmited with 2 channel audio. Which make me think that the audio engine do some kind of downmix for channels with 5.1 audio in this case.

Attachments (1)

sample.mpg (500.0 KB) - added by benny@… 11 years ago.
A small sample from "Discovery Channel" where upmix fails

Download all attachments as: .zip

Change History (5)

comment:1 Changed 11 years ago by anonymous

Adding some further comments:

  • Setting upmix to "Best" but still not works for all channels. In my case with the "Discovery Science" channel I got this weird behaviour. Looking in log from mythfrontend
    2010-06-30 19:40:54.534 AFD: Opened codec 0x7ffb9a190180, id(MPEG2VIDEO) type(Video)
    2010-06-30 19:40:54.534 AFD: codec MP2 has 1 channels
    2010-06-30 19:40:54.534 AFD: Opened codec 0x7ffb98008b90, id(MP2) type(Audio)
    2010-06-30 19:40:54.542 AO: Opening audio device 'iec958' ch 2(1) sr 48000 sf signed 16 bit reenc 0
    2010-06-30 19:40:54.544 Opening ALSA audio device 'iec958'.
    2010-06-30 19:40:54.958 VideoOutput: Created YV12 OSD.
    2010-06-30 19:40:59.376 TV: Attempting to change from WatchingLiveTV to None
    2010-06-30 19:40:59.603 VSYNC: ~OpenGLVideoSync()
    2010-06-30 19:40:59.603 OpenGL: Deleting OpenGL Resources
    2010-06-30 19:41:00.675 TV: Changing from WatchingLiveTV to None

This make's me believe that this channel is sent with MP2, 1 channel only (Mono) and maybe that is what causes the problem.

comment:2 Changed 11 years ago by JYA

Status: newinfoneeded_new

Upmixer only works with stereo input.

A mono-playback will not be upmixed, you just can't. Upmixing to 5.1 use the weighted values between the left and right channel to identify which channel it should go to.

Depending on what your hardware support, mono input will be duplicated on left and right channels

If this is what you mean by "wierd" behaviour, this is what's intended

Changed 11 years ago by benny@…

Attachment: sample.mpg added

A small sample from "Discovery Channel" where upmix fails

comment:3 Changed 11 years ago by JYA

Status: infoneeded_newnew

a 500ko sample is not going to help ... 30MB would be better.

comment:4 Changed 11 years ago by JYA

Resolution: fixed
Status: newclosed

(In [25244]) Do not try to upmix mono audio into 5.1, should fix #8627

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