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View Full Version : Audio flagged as "variable/constant bitrate" question

madhatter300871
19th February 2011, 16:46
I have an audio stream that mediainfo flags as being a TrueHD DTS track with a variable/constant bitrate.

My question is, how is that possible ? I thought it could only be either constant bitrate or variable bitrate.

Incidently, this is one of the few videos I have with lip synch issues. Strangely, the first minute or so is out by about 1 second, and regardless of what delay I introduce (in the region of +/- 100ms) the rest of the movie drifts in and out of synch (only by this small amount of 100ms or so).

Any ideas what variable/constant bitrate audio is as I am thinking this must be the cause of the strange synch issue.
kieranrk
19th February 2011, 19:46
"TrueHD DTS track" makes no sense.
mp3dom
19th February 2011, 20:54
TrueHD dts doesn't exists. It can be Dolby TrueHD or dts-HD. The constant/variable is possible because both Dolby and dts encoding schemes are built on a 'core' packet (that is lossy and constant) and an 'extension' packet that is variable. The constant part is like old encoding (Dolby Digital or dts Surround) and is available for compatibility with old equipment. The variable part contains the extension to obtain true lossless audio. The elder equipment will play/see only the constant and lossy part (in general Dolby at 640 Kbps or dts at 768 Kbps or 1500 Kbps) while the new decoders will play the full lossless audio.

I don't think the lipsynch issue is due to the constant/variable audio.
Blue_MiSfit
20th February 2011, 07:34
Thread moved to Audio Encoding subforum. Please post in the appropriate place :)

Cheers,

Derek
madhatter300871
20th February 2011, 15:32
My mistake, it's 640Kbs AC3 TrueHD track. Been looking at it for so long I just mistyped to DTS without paying attention.

I know the TrueHD is built on a core track for backwards compatibility, I didn't put 2 and 2 together on this one, thanks mp3dom. That explains constant/variable at the same time.

I have extracted the core track and it is this track I am having the problem with, I'll try a few more things now I know what the constant/variable flag is.

Thanks.