downloaded dash streams should not be given m4a extensions

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al_9x
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downloaded dash streams should not be given m4a extensions

Post by al_9x » Fri Nov 28, 2014 4:20 pm

it's not a mp4 container it does not have the m4a ftyp, and without m4a remuxing won't play in ios
Last edited by al_9x on Sat Nov 29, 2014 7:14 pm, edited 2 times in total.
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therube
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Re: downloaded dash streams should not be given mp4 extensio

Post by therube » Fri Nov 28, 2014 10:31 pm

> it's not a mp4 container

Then what is it?
.264? .avc?

> and without conversion

Conversion how? To what?
Are you just putting it into a different container or you actually transcoding it?

> won't play in for example ios

Is that a limitation of iOS, lack of mpeg-dash support?
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Re: downloaded dash streams should not be given mp4 extensio

Post by therube » Sat Nov 29, 2014 1:38 am

> mp4 extension

Who assigns the extension?
In my case Youtube comes down as "videoplayback".
How is it determined?
mime-type?

https://r4---sn-p5qlsnsk.googlevideo.co ... io%2Fmp4 ...

Content-Type "audio/mp4"

https://r4---sn-p5qlsnsk.googlevideo.co ... eo%2Fmp4 ...

Content-Type "video/mp4"
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al_9x
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Re: downloaded dash streams should not be given mp4 extensio

Post by al_9x » Sat Nov 29, 2014 7:10 pm

it turns out it's a little more complicated, mp4 has many subtypes (ftyp)

the expected ftyp of an m4a file is M4A$20, but dash aufio streams are ftyp dash, so at least the m4a extension is wrong.
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Re: downloaded dash streams should not be given m4a extensio

Post by therube » Sat Nov 29, 2014 9:53 pm

So again, if not .m4a, then what do you suggest?

.aac?
(And assuming you're getting "mp4" + "m4a".)


What I do (& somewhere along the line I need to specifically name the files) is to name the video; filename.mp4, then the associated audio; filename.m4a.mp4.

In my case, these downloads go into a specific directory tree.
So from there I just search (http://www.voidtools.com/) for "dirpath: .m4a" & anything that turns up there I know I've got to mux. And still with Everything, I copy the audio / video pathnames into clipboard, then paste those pathnames into the program I use for muxing (http://www.videohelp.com/tools/Video-to-Video-Converter).

(VtV needs an update to MediaInfo in order to recognize Dash, http://mediaarea.net/us/MediaInfo/Download/Windows.)
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Re: downloaded dash streams should not be given m4a extensio

Post by therube » Thu Dec 04, 2014 8:29 am

(I'm sure you know, but I thought it was well written, so...)
First of all MP4 (actually "MPEG-4 Part 14") is a container format. It describes how data is arranged in a file, but is does not describe how the audio and video is compressed. Though, MP4 files may contain a variety of different audio formats (such as MP2, MP3, AAC, AC3) and a variety of different video formats (such as MPEG-2, MPEG-4 ASP, H.264/AVC and H.265/HEVC).

Now, MP4 files may be audio-only (contain only an audio stream), they may be video-only (contain only a video stream) or they may contain audio plus video. In all of theses cases, it's still simply a MP4 file. And using the .mp4 file extension would be correct in all these cases. Anyway, since file managers (like Windows Explorer) usually look at the file extension to decided which application they open a file with, and since people may which to open "audio" MP4 files with a different application than "video" MP4 files, this has lead to the practice of using the .m4a and .m4v extensions for audio and video MP4 files, respectively. Technically, these .m4a and .m4v are still in the MP4 format. There is no M4A or M4V "format".

http://forum.doom9.org/showthread.php?t=171350
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