Opened 14 years ago

Closed 12 years ago

#2813 closed defect (duplicate)

Need to support 32khz AC3 stream pass through

Reported by: ylee@… Owned by: Isaac Richards
Priority: minor Milestone: unknown
Component: mythtv Version: head
Severity: medium Keywords: ac3 32khz 32k spdif s/pdif optical audio sound digital firewire
Cc: Ticket locked: no


I have the same issue that Rob Baumstark and others report at when playing back certain Firewire recordings (ones with 32khz AC3 tracks) from certain basic-cable channels with my Turtle Beach Riviera's S/PDIF output to a receiver. As Rob notes, both audio and video are "chipmunk"-like sped up, along with occasional loud pops that sometimes cause my receiver to shut down (presumably to protect the speakers from physical damage).

As Rob writes:

I'm pretty sure at this point that what I need is MythTV to check the sample-rate of AC3 streams before it attempts to pass them through, and automatically disable AC3 passthrough for streams that are not 48khz. I have yet to see an AC3 stream thats not at 48khz and that also contains more than 2 channels, so there would be no loss of surround-sound with such an option.

In the meanwhile, a workaround is to alter the playback speed to something other than 100%; this forces MythTV to remix the AC3 track to 48khz.

Change History (4)

comment:1 Changed 14 years ago by ylee@…

Keywords: firewire added
Summary: 32khz AC3 tracks are bad for my receiverCertain basic cable-channel FireWire recordings' audio tracks cause problems for receiver

I should also note that the word "certain" is important. The audio from the recording of one film from Turner Classic Movies will be fine, while the recording of the next film on the channel will have the audio issue. It's not the (pre-Dolby and usually pre-stereo) movies themselves; typically both affected and unaffected recordings starts with TCM's own commercials in between the recordings. If the audio issue exists at the beginning of the recording, it will affect the entire recording; otherwise, no problems. Since the audio issue also exists when playing the affected recordings through mplayer, I must assume that it has something to do with the FireWire? recording portion of mythbackend, as opposed to mythfrontend's audio-decoding code. I have changed the Summary line accordingly.

PS: In case it's not clear, "basic cable channel" = analog cable channels, which on my system and on most others' are those under 100. 100 and above mark digital cable channels.

comment:2 Changed 13 years ago by danielk

Summary: Certain basic cable-channel FireWire recordings' audio tracks cause problems for receiverNeed to support 32khz AC3 stream pass through
Version: 0.20head

comment:3 Changed 12 years ago by foobum@…

#5900 will fix

comment:4 Changed 12 years ago by Dibblah

Resolution: duplicate
Status: newclosed
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