5.1 ch AAC plays back slooow via ffdshow

[absinthe]

I've encoded a 5.1 ch soundtrack from AC3 via MeGUI and for some reason it plays back slooooooooooow. It does this alone as an audio-only file, and when muxed in with the video the whole thing plays slow.

Oddly, it only seems to do this in Media Player Classic (decoded by ffdshow). If I play the file in Nero Showtime or in VideoLAN, it plays fine.

This seems to hold true regardless of the 5.1 ch settings I use. However, it does not happen if I downmix to stereo. This has happened with multiple files. I'm using the latest BeSweet files.

I've searched on this but can't find anything. Ideas? An ffdshow setting?

-abs

[SeeMoreDigital]

A similar thing happened to me a while back with 6Ch AAC and ShowTime player.

I found the problem went away by de-selecting "Use SPDIF" via the "Audio Output" options. But with FFdshow's filters I don't know....

Is the sample rate of your 6Ch AAC stream 48kHz?


Cheers

[absinthe]

Well, it came from a DVD and I didn't select any resampling options in the GUI ... so, unless it automatically did that (and I don't see why it would) I'd have to assume it's 48 kHz.

-abs

edit: Well, if MP4UI is to be believed, the sampling rate is 24000. Whoa!

-abs

[SeeMoreDigital]

Well, if MP4UI is to be believed, the sampling rate is 24000. Whoa! Did you select AAC-HE for you audio output? If so 24,000Hz is correct!

Anyway, I seem to remember FFDshow offers adjustment over the "AC3 Output" sample frequency. Off the top of my head I can't remember where this setting is (there's a thread about AAC to AC3 transcoding somewhere) but you'll need to make sure it's set to 48kHz and not 44.1kHz.


Cheers

[absinthe]

Did you select AAC-HE for you audio output? If so 24,000Hz is correct!

Anyway, I seem to remember FFDshow offers adjustment over the "AC3 Output" sample frequency. Off the top of my head I can't remember where this setting is (there's a thread about AAC to AC3 transcoding somewhere) but you'll need to make sure it's set to 48kHz and not 44.1kHz.Actually, this one is AAC-LC, but it does the same thing with HC encoding settings.

Interestingly, if I open the file in GraphEdit it apparently is decoded by Nero (the audio, that is), though the file plays fine in Nero.

VideoLAN plays the file just fine, and reports the audio track to be 48 kHz.

??

-abs

[SeeMoreDigital]

Actually, this one is AAC-LC, but it does the same thing with HC encoding settings. Well I'm surprised that mp4UI identifies the 6Ch AAC-LC stream as being 24kHz, when it should be 48kHz... It would seem FFdshow is also identifying the stream as being 24.24kHz and playing it at half speed :eek:

Have you tried generating a new 6Ch AAC-LC audio stream and re-muxing it?


Cheers

[absinthe]

If I run mp4creator from the command line, the track is identified as 48 kHz. So perhaps you are right and ffdshow is identifying it as 24 kHz. I've tried encoding several of these 5.1 files several times, as both HC and LC. I'll try again.

This all seems odd: Video alone plays back normally via ffdshow. Audio alone plays back normally in MPC (apparently decoded by Nero). But mux the audio with the video, and suddenly it's slow in MPC (ffdshow/Nero) but normal in Nero Showtime or VideoLAN.

-abs

[absinthe]

Well I installed the CoreAAC DirectShow filter. That seems to have solved the problem.

thx,

-abs

[yaz]

Actually, this one is AAC-LC, but it does the same thing with HC encoding settings.and u're sure it wasn't mux as he-aac, aren't u ? (just because it's my usual way of getting audio at half speed ;) ) anyway ... afaik, 'core' does not tackle w/the 'he-flag' (it uses a different way of identification) but 'real' does. the latter is implemented in ffdshow.

the bests
y