AAC 5.1 to AC3 5.1 - What's the best way?

[glen8]

Hi all,

I have been encoding a lot of my personal bluray movies to MP4. The method I generally use it via RipBotX264. I downscale then to 720p as I only want the output file to be around 5GB and convert the audio from the HD track to 5.1 AAC. The results have really been fantastic.

Now I want to have two soundtracks within the MP4 file. I have extracted all the streams from the MP4 as follows with MP4BOX

H264 Video
5.1 AAC Audio
Chapters
Poster

I'm trying to convert the AAC audio into 5.1 AC3 and then repackage everything back up so the MP4 has two soundtracks. The reason for this is that I want to only have the one movie file which works on my portable devices (AAC) and have 5.1 sound from my home theater (AC3).

Yesterday after a lot of searching around I managed to convert AAC to AC3 but when playing back once I have selected the AC3 sound track I have terrible lip sync.

Just wondering what's the best way of converting it. Also, will it loose much quality.

[tebasuna51]

Recoding always loose quality, but not much if you select a bitrate according with the source.

Try with:

NeroAacDec -if your.mp4 -of - | Aften -readtoeof 1 -b 448 - output ac3

[glen8]

Recoding always loose quality, but not much if you select a bitrate according with the source.

Try with:

NeroAacDec -if your.mp4 -of - | Aften -readtoeof 1 -b 448 - output ac3

Thanks, will try it later today