Add warning to documentation that merging DASH video requires newer avconv

[maxb]

Hi,

I just downloaded my first DASH Video+Audio, and had some difficulty figuring out how to stitch them together. avconv seemed to not be able to properly read the DASH video in copy mode.

Eventually, I tried upgrading my installation of libav from 0.8.9 (available in the current Ubuntu release) to 9.10 (I got it from the Ubuntu development version), and this fixed the issue.

It would be nice if youtube-dl's documentation contained a warning that avconv 0.8.x has problems handling DASH video, and suggested upgrading to avconv 9.x.

The specific video I was downloading was http://www.youtube.com/watch?v=hpNp8WdQOoo format 137, though I also tested a number of the lower quality DASH video formats with the same results.

[rbrito]

@maxb, can you please let me know what you tried? The 0.8 version of libav should be good enough for muxing audio and video. See my post here:

http://cynic.cc/blog/posts/2013-10-23-assorted_news/

The relevant excerpt is also what I included in Debian's packaging of youtube-dl:

https://github.com/rbrito/pkg-youtube-dl/blob/master/debian/NEWS

[wyatt8740]

... or ffmpeg, which most of the world still uses.
(I compiled it myself to avoid the weird syntax of libav in ubuntu.)

In ffmpeg 2.1/2.0/1.2.1/1.2:
ffmpeg -i DASH_VIDEO.mp4 -i DASH_AUDIO.mp4 -vcodec copy -acodec copy DASH_AVMUX.mp4

[MDCore]

@rbrito I'm on Ubuntu 13.10. If I do:
avconv -i video.mp4 -i audio.m4a -codec copy output.mp4
I get a muxed output with only audio. the results say the video portion is 0kb

any ideas?

More info:
Using avconv version 0.8.9-6:0.8.9-0ubuntu0.13.10.1

Stream mapping:
  Stream #0:0 -> #0:0 (copy)
  Stream #1:0 -> #0:1 (copy)
Press ctrl-c to stop encoding
frame=    0 fps=  0 q=-1.0 Lsize=   29090kB time=1856.71 bitrate= 128.3kbits/s    
video:0kB audio:28465kB global headers:0kB muxing overhead 2.197169%

any ideas?

[maxb]

@rbrito Sorry I've taken so long to respond here, I had a fairly crazy week at work. MDCore's description is in agreement with what I saw.

Here are the exact commands I ran:

youtube-dl -f 139 -o 139.m4a hpNp8WdQOoo
youtube-dl -f 134 -o 134.mp4 hpNp8WdQOoo
avconv -i 139.m4a -i 134.mp4 -c copy out.mp4

(I've chosen lower quality format codes in the above example to be kinder on the time and bandwidth of people just wanting to verify the bug.)

The out.mp4 produced by libav-tools 0.8.9-0ubuntu0.13.10.1 is far too small to contain any video data, and avprobe reports that it contains only an audio stream.

Switching to 9.10-1ubuntu1 with no other changes instead produces a successful combined file.

[MDCore]

@maxb I've searched high and low but I can't find out how to switch to 9.10-1ubuntu1 in Saucy. Do I need to compile from source?

[maxb]

@MDCore I did it the "advanced APT shenanigans" or possibly just "evil" way - I reconfigured APT to include Trusty Tahr sources, and applied the relevant black magic in /etc/apt/preferences to ensure I only got what I wanted from Trusty.

For the record, the process goes like this:

1. Add "deb SOME-MIRROR-URL trusty main universe" to /etc/apt/sources.list

2. Add exactly the below to /etc/apt/preferences (it probably doesn't exist - create it):

Package: *
Pin: release n=trusty
Pin-Priority: 400

3. apt-get update

4. apt-get install -t trusty libav-tools

Bear in mind that if you go through with the above, it's firmly into the area of unsupported black magic, and it is CRITICAL you undo the changes to /etc/apt/sources.list and /etc/apt/preferences before attempting to upgrade fully to Trusty in the future, or bad stuff will happen to the upgrade.

[MDCore]

Thanks for documenting the process @maxb, even though I don't think I'm going to risk it! Hopefully someone will make a PPA.

[maxb]

@MDCore Well, since you asked :-) - deb http://ppa.launchpad.net/maxb/trusty-libav-for-saucy/ubuntu saucy main

It's the exact same packages you'd end up with from the previous method (i.e. the ones currently in the Trusty repository), but making use of Launchpad's ability to copy selected packages into a new PPA to avoid the complexity of needing to configure filters on the client side to affect what packages you get.

[MDCore]

@maxb Wow! I added the ppa, updated libav and ran the same test as before. It worked perfectly!

How can I thank you?

[Vdragon]

I got the same result as @MDCore and @maxb in Ubuntu 13.10, please make it verify ffmpeg/libav 's version to make sure it will convert correctly 👍

sample: http://www.youtube.com/watch?v=bDeG_YFl-b0

[mrvanes]

@maxb You saved my day! Thx for the repo and fix!

[healthyfood]

'stiching' m4a/mp4 dash videos works fine. stitching webm video and audio together fails with a "ERROR: Could not write header for output file #0 (incorrect codec parameters ?): Invalid argument". Not much love for webm.

[s-gv]

I had the same problem of no video output when muxing 1080p DASH video and audio got from youtube using avconv on Ubuntu 12.04. This worked for me:

MP4Box -add video_only.mp4 -add audio_only.m4a -new combined.mp4

[phihag]

youtube-dl will now warn automatically if it finds an overly old ffmpeg or avconv version. Thanks for the report!

[wyatt8740]

It's good that this is fixed. But I'd like to say again that if you have this problem with a recent avconv build, you should really give ffmpeg a try. Sometimes things work in ffmpeg that don't in avconv.