IPB

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
Extracting AAC-vbr from mpeg4 video
lolly2de
post Jul 11 2014, 18:36
Post #1





Group: Members
Posts: 2
Joined: 11-July 14
Member No.: 116657



Hi

is there a way to extact a vbr aac-audio track from a mpeg4-video file? After using syntax:

ffmpeg -i infile.mp4 -map 0:x -acodec copy outfile.m4a (where x is audio track)

the extracted m4a-file shows cbr. How can I preseve vbr of the extracted audio? Any ideas welcome.

TIA.
lolly
Go to the top of the page
+Quote Post
huokok
post Jul 11 2014, 20:00
Post #2





Group: Members
Posts: 14
Joined: 11-February 14
Member No.: 114443



How can you confirm the original audio track is vbr? By MediaInfo? Why does it matter?
If ffmpeg shows it is stream copy, then IMO it should be the original audio stream, no matter what MediaInfo tells.
I did a few test, right, ffmpeg created m4a file will always show as cbr in MediaInfo wacko.gif , but there won't be any difference about audio streams. You can confirm by bit-compare using fb2k.

So, if you really care about MediaInfo, I would suggest you to use mp4box
CODE
mp4box -add "input.mp4#audio" "output.m4a"

Alternatively, you can simply remux your m4a through mp4box.

This post has been edited by huokok: Jul 11 2014, 20:02
Go to the top of the page
+Quote Post
lolly2de
post Jul 11 2014, 20:09
Post #3





Group: Members
Posts: 2
Joined: 11-July 14
Member No.: 116657



thanks huohok for your considerations. Indeed, I did analysis by MediaInfo. Will check out mp4box.
Go to the top of the page
+Quote Post
Zenitram
post Jul 12 2014, 12:38
Post #4





Group: Members
Posts: 7
Joined: 30-August 05
Member No.: 24206



QUOTE (lolly2de @ Jul 11 2014, 19:36) *
the extracted m4a-file shows cbr. How can I preseve vbr of the extracted audio? Any ideas welcome.

You do a raw copy, so no difference in your stream.
The detection of CBR/VBR in the MP4 file may be wrong.
I need the files (in and out) for patching that in MediaInfo.

Jérôme, developer of MediaInfo.


--------------------
MediaInfo: http://mediaarea.net/MediaInfo
Go to the top of the page
+Quote Post

Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 28th November 2014 - 00:34