mp4 (h.264) Demuxing: Is it possible to save a step when encoding to ac3

[Krelmaneck]

Here is the deal:when demuxing AAC Audio from an mp4, is it possible to to demux straight to a wav file and then to AC3, thus saving an intermediate step?

You say. Of course, that is easy. Well, the goal is to save as many generations as possible-- the less encoding the better.
If I want to encode the aac to ac3 for DVD muxing, doesn't it sound ludicrus if I have to go from demuxing a mp4(h.264/mpeg 4 avc) track with YAMB to creating a wav file with another program and then using AFTEN or AFTEN Gui a little repetitive? I know that DGAVCindex can demux as well--and demux the audio straight to a wav file if I am not mistaken---and DGAVCdecode is the avisynth decoder I use for encoding BUT the DGAVCindex only likes raw h.264, thus making YAMB a good first step for demxuing the tracks to raw (MAYBE--and that is a big maybe).

You see, when it comes to AVI, eveyone can use virtualdub to save the audio to a WAVE. Good for AVI's/ Now let's get back on track.

MP4's can't be fed into virtualdub yet.

Are you stating to understand my point now? Wouldn't it be nice if there was a program that could take the mp4 (h.264/mpeg 4 avc) and extract the audio to a wave and then have the h.264 go to a raw h.264 for DGAVCindex? I mean, the MKVextract, does exactly what I want to do BUT i have an mp4 not MKV. Virtualdub can do this for AVI's. But mp4, it looks like I am stuck with a reptitive step or a tripple encdoing of audio.



IF YOU CANNOT UNDERSTAND MY POINT, HERE IS A STRAIGHT TO THE POINT VERSION BELOW:



Here is my illustration for Audio AAC to ac3 for DVD in an mp4 container

YAMB ---> ANOTHER PROGRAM TO ENCODE IN WAV--AFTEN or AFTEN GUI for AC3 dvd specs.


This is what I want to happen
PROGRAM 1 (demuxes to raw h.264 AND saves audio as wave)--- Program 2 (AFTEN wav to ac3)


My analogy:
Since there is a way to do this with an MKV (mkvextract), wouldn't you think there would be the same process for mp4 (h.64) files so you could save one generation of audio encoding?


I am saying:
I WISH you could feed DGAVCindex wih a regular mp4 h.264 then that would save me a step and one less encode. Actually, steps are great. Degrading one generation of audio--not that great. But unfortunately, the h.264 has to be demuxed to raw h.264 with another program such as yamb before it can be loaded into dgavcindex.



Conclusion:

Is there any way around this so there is one less step of encoding the audio. Encoding the audio 3 times sounds ludicrus if you know what I mean. And what do I mean by encoding audio 3 times--demxuing audio from mp4 to aac-->aac to wav--->wav to ac3. Now, that we are on the same page--anyone want to offer any suggestions?

[Soopafresh]

mp4_to_ac3.zip





Ffmpeg at a high enough bitrate (320k or higher) will sound just as good as Aften's ac3 transcoder

If you insist on using Aften, download this instead

mp4_to_wav_to_ac3.zip

[TJohns]

You realize that the first step from AAC -> WAV doesn't lose anything? It just relies on the "accuracy" of the decoder to re-create the original stream ... trying to do it all in one step just relies on something else to "internally" decode to wave file then re-compress it again.

[Soopafresh]

Try this http://www.videohelp.com/tools/TFM_Audio_Tool

[AlanHK]

Is there any way around this so there is one less step of encoding the audio. Encoding the audio 3 times sounds ludicrus if you know what I mean. And what do I mean by encoding audio 3 times--demxuing audio from mp4 to aac-->aac to wav--->wav to ac3. Now, that we are on the same page--anyone want to offer any suggestions?

You may want to streamline the process, but actually there is no extra loss in going through WAVE, as it is uncompressed, so no quality gain if you eliminate that.