Is re-encoding only audio possible with HB?

General questions or discussion about HandBrake, Video and/or audio transcoding, trends etc.
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markog
Posts: 4
Joined: Thu Oct 02, 2014 12:31 am

Is re-encoding only audio possible with HB?

Post by markog »

Hello, guys,

Is it possible to re-encode only audio from a movie and leave the video portion intact?
I'm asking because some smart TVs can't play certain audio codecs (DTS, for example)
so I have to re-encode a movie to watch it on TV. It would be much easier (and faster)
if it was possible to re-encode only audio. If anybody can help, I'd appreciate it.

Marko

rollin_eng
Veteran User
Posts: 3380
Joined: Wed May 04, 2011 11:06 pm

Re: Is re-encoding only audio possible with HB?

Post by rollin_eng »

No.

markog
Posts: 4
Joined: Thu Oct 02, 2014 12:31 am

Re: Is re-encoding only audio possible with HB?

Post by markog »

Strange, as Auto pass through is available for audio. I'd like to know why the same can't be implemented for video. Thanks.

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JohnAStebbins
HandBrake Team
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Joined: Sat Feb 09, 2008 7:21 pm

Re: Is re-encoding only audio possible with HB?

Post by JohnAStebbins »

Not all sources have perfectly synchronized audio and video. Some players will compensate for this and some won't. HandBrake fixes this while transcoding by dropping audio/video frames or inserting silence/black frames.

You can drop individual frames of encoded audio without damaging previous or following frames. Video does not work the same. If you drop one frame of encoded video, it can damage an entire sequence of video frames. You also can't insert random black frames in the middle of a video sequence for the same reason. Encoded video frames are not independent. They require information from the frames surrounding them to be decoded properly. Thus if you want to drop or insert anything, you must re-encode.

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JohnAStebbins
HandBrake Team
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Re: Is re-encoding only audio possible with HB?

Post by JohnAStebbins »

FYI, bluray and dvd sources are a perfect example of a type of source with frequent small audio/video de-sync. A BD/DVD title can be composed of a sequence of m2ts/vob files. The audio and video of each m2ts/vob file starts at the same timestamp, but they do not end at the same timestamp because audio frames and video frames do not have the same duration. After the first frame, subsequent audio and video frame boundaries never align. The BD/DVD spec accommodates for this be defining that there will be a small amount of overlap between segments that the player is supposed to drop after decoding the initial frame of a segment.

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