Mailing List Archive: MythTV: Users

mythtranscode sometimes breaks sound

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michael_zanetti at gmx

May 22, 2010, 3:26 AM

Post #1 of 2 (405 views)
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mythtranscode sometimes breaks sound

Hi all,

Lately I decided to transcode some of my recordings to mp4 to save some disk
space. I modified the "Low quality" transcoder preset to the following
settings:

Codec: MP4
Bitrate: 1000 kb/s
Sound: MP3
Samplerate: 44100
Volume: 100%
Everything else is left at its default value.

This seems to compress a movie from the original 3GB to about 1GB with still
quite good quality. However, now that I have transcoded some of my recordings,
I noticed that this sometimes breaks sound. Sound is still there, but pitched
down. It's like the sound would play only half of its speed while the video
plays at its correct speed.

Note, that not every transcoded movie is broken. Only about every 5th one. Is
this a bug in mythtranscode or my owns fault in configuring the transcoder?

Anyone has an idea how to repair those movies or are they lost forever? I
already tried re-transcoding using a the "lossless" setting for mythtranscode.
Doesn't fix the sound though...

Thanks in advance,
Michael

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mythtv at rodsbooks

May 22, 2010, 6:54 AM

Post #2 of 2 (396 views)
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Re: mythtranscode sometimes breaks sound [In reply to]

On 05/22/2010 06:26 AM, Michael Zanetti wrote:
> Hi all,
>
> Lately I decided to transcode some of my recordings to mp4 to save some disk
> space. I modified the "Low quality" transcoder preset to the following
> settings:
>
> Codec: MP4
> Bitrate: 1000 kb/s
> Sound: MP3
> Samplerate: 44100
> Volume: 100%
> Everything else is left at its default value.
>
> This seems to compress a movie from the original 3GB to about 1GB with still
> quite good quality. However, now that I have transcoded some of my recordings,
> I noticed that this sometimes breaks sound. Sound is still there, but pitched
> down. It's like the sound would play only half of its speed while the video
> plays at its correct speed.

I've had this problem, too, but only on one of my two backends (the one
that runs Ubuntu 9.10; the one that runs Gentoo is fine) and only on
videos that have 5.1 audio. If the original source has 2-channel audio,
it's fine. This problem has persisted for ages.
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