Audio transcode, target media is DVD

[Avisynth_challenged]

Hey all,

I pulled a mp4 clip from the web and would like to convert the clip to MPEG2 video with either AC3 or 16-bit 48KHz wave audio, which will ultimately be written to DVD.

At the moment, I believe I have what I need for the video side.

For the audio, however, I'm not sure what to do.

The clip has the following audio properties:

Codec: MPEG AAC Audio (mp4a)
Language: English
Channels: 2-channel stereo
Sample rate: 44100Hz

The task, as far as I can tell, would require the following steps:

1. Demux the AAC audio stream.

2. Transcode to either AC3 (with 48000Hz sample rate, and maybe 192kbps) or WAV (with 48000Hz sample rate, 16-bit, stereo 2-ch, maybe uncompressed CD quality 1411.2kbps).

3. Use the output of step 2 as an elementary stream to author a DVD of the transcoded clip.

Is this a reasonable approach? If so, what would be a good tool to carry out step 1 (demuxing the audio from the original clip)? I tried the conversion wizard in the latest VideoLAN, but could not get it to work.

Any feedback or suggestions would be greatly appreciated. Thank you very much.

[mariush]

Leave it uncompressed wav if it would fit a DVD. No point in losing more quality by re-encoding it to WAV.

Use Foobar2k to export to WAV or avs2wav or ffmpeg or whatever.... i never got VLC to convert anything properly.

[Avisynth_challenged]

Thanks for the response.

Any idea how to demux the AAC audio out of the mp4 container so that the audio can be treated in isolation from the video? Or do the tools you listed read mp4 files natively?

[tebasuna51]

You can decode the audio directly from mp4 container with NeroAacDec:

NeroAacDec -if clip.mp4 -of audio.wav

[Avisynth_challenged]

You can decode the audio directly from mp4 container with NeroAacDec:

NeroAacDec -if clip.mp4 -of audio.wav

Wow, that works great. Quick question... is there a command-line switch in NeroAacDec that can change the sample rate from 44100Hz to 48000Hz?

[tebasuna51]

Nope, NeroAacDec is only a decoder but you can pipe the output to sox

NeroAacDec -if clip.mp4 -of - | sox --ignore-length - audio.wav rate 48000