Got a tip for us?
Let us know
Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
HandBrake: Problem converting MKV to mp4
- Thread starter ypn
- Start date
- Sort by reaction score
Thanks for your kind response. But A52Codec seems to support only 2 ch audio.
To avoid complexity, I guess I better to use Win as I heard that ffmpeg's aac encoder for Win is better than Mac's. How's audio quality encoded by XMedia?
Last edited:
I thought that's what you were trying to achieve, Dolby Prologic II AAC stereo, and you were not happy that MP4tools used ffmpeg to produce it and you wanted an app that used CoreAudio, like HB, but without the video compression.
Are you sure you know what you really want?
I'm very sorry that you are confused by my message. You absolutely right. I am looking for an app that used CoreAudio without the video compression. Subler would be a perfect app if I could solve the Perian-ML issue. A only problem is I want to also encode 5.1 ch audio to 6 ch discrete aac. According to the following site, A52Codec support only 2 ch audio. I have tried Pavtube Video Converter but this app supports only up to 256 kbps for aac conversion of 5.1ch surround.
http://www.techisky.com/how-to/solve-subler-mountain-lion-passthrough-ac3-audio-issue.html
I don't know the specifics of your situation or knowledge, but here is what is normally done with audio for compatibility with the aTV and other iDevices (iPod, iPad, etc).
1st track should be AAC Dolby Prologic II:
That give compatibility with devices that only have stereo outputs or AVR's that use Dolby Prologic to create a "synthetic" surround sound
2nd track should be either AC3 passthrough or 6-channel discrete:
That provides 5.1 channel surround sound to AVR's that can handle the individual audio channels. AC3 passthrough is used for Dolby Digital 5.1 sources and 6-channel discrete is used for DTS sources (at least that is the way Handbrake is set up)
So if you are just changing containers and your source is Dolby Digital 5.1, just use pass-through. If your source is DTS, it will need to be converted to either AC3 or 6-channel discrete. And of course, you will have to add the AAC Prologic track. It's really kind of PITA to do all this if you don't use Handbrake (which it sounds like you don't want to do) or MP4Tools. But with enough effort, it can be done. Lot's of others worried about original vs transcoded quality and transcode time do it. Personally, I think the quality, reduced file size and streaming quality that Handbrake provides with worth a small, possibly even imperceptible, quality decrease and transcode time.
But to each his own.
Actually, I did not realize that apple TV accept Dolby Digital 5.1 surround sound pass-through. Because Quicktime cannot play AC3, I though 5.1 surround sound have to be encoded to play via apple TV.
Thanks for your valuable comments, which would be extremely helpful as I have poor knowledge about video encoding. Thanks again for your kindness!
I do the PITA way when it comes to the audio. It's the only way to achieve consistency, and correctly control things like DRC, DialNorm, phaseshift, downmix matrix, and good average RMS volume that doesn't cause you to turn the volume up and down all the time due to low dialogue volume and loud explosions, etc.
It will require a professional audio waveform editor, encoder, and command line tools, and I understand most people don't wanna go this way.
However, all manipulation with audio will degrade quality. For example, I still feel the AC3 and AAC tracks in movies from iTunes stores sound very good, compared doing our own DTS to AC3 or DTS to stereo AAC. It's likely because they start out with the master audio source file, being so much higher quality. They also have professional experience in mastering the audio, when it comes to compressors and limiters.
----------
I can play M4V/MP4 files in QuickTime with AC3. So there seems to be an AC3 decoder bundled with QuickTime or iTunes, or whereever it came from. Of course, it gets downmixed on my laptop since it only has stereo speakers.
Actually, I would only need an 5.1 AC3 track for all purposes since it can be downmixed by the decoder, but there is no AC3 decoder in iOS. So for iOS devices, one still need to produce a stereo AAC track... sigh.
I installed an AC3 codec and now I can play a 5.1 AC3 track with Quicktime. Do you think a 5.1 AC3 track downmixed by the decoder is close to a 2ch track downmixed by Pro Logic II?
The type of downmix is controlled by a metadata in the AC3 file that the decoder uses. This downmix is usually of two types; normal stereo, or Dolby Pro Logic. So you can get either of those two depending on what the metadata says. So to my knowledge you cannot get Dolby Pro Logic II from a standard AC3 decoder. A Dolby Pro Logic II track can sound a lot more 'surroundish' than the other two.
When I encode my own AC3 files I usually set the metadata to indicate a normal stereo downmix, because I don't want surround effects that require phaseshifting. If you don't know where your original audio source file came from, you might end up with double phase shifting, or no phaseshift but a downmix that requires phaseshift, and so forth, which will just make it sound wrong.
No problem. Just don't go my path when it comes to audio conversion.
I've had a personal interest in learning about audio, but I think I'm done now. It really isn't worth pursuing the quest of building a perfect stereo AAC track for me anymore. If there is no stereo track on my source, whether it be DVD, Bluray, or some other source, I don't bother anymore. For surround, I only use AC3 for consistency, making sure it has the correct metadata and preprocessing.