Re: [gentoo-user] viewing .m4v files with totem

[Stroller]

On 9 Jul 2010, at 02:50, Allan Gottlieb wrote:

> How should I view .m4v files with totem.
> Is there a gst-plugin or a use flag for gst-plugins-meta?
>
> I have used the following, which "works", but the video quality is bad
> ffmpeg -i file.m4v file.avi
> totem file.avi

Hi there,

I was been reluctant to reply earlier, because I'm not a real expert  
on the subject, but .m4v is a *container format*, as is .mp4  
and .avi. .avi is actually a poorer one.

http://en.wikipedia.org/wiki/.m4v

I believe any of these containers can contain a variety of video /  
audio *codecs*. There are still loads of files floating around which  
use old Windows-centric codecs, but h264 is becoming the most common  
video codec. A container might contain the audio as MP3, AAC or  
something else.

So it's not clear from just saying "convert from one file format to  
another" whether you converted the audio &/or video from one codec to  
another (known as "transcoding") or whether you just took the existing  
audio &/or video and simply put it in a different container (known as  
remuxing, I believe). A few minutes of video in an undemanding codec  
might be transcoded to shitty quality in a matter of minutes, nearly  
as quickly as remuxing a large video. The latter would depending on  
the speed of your disk / filesystem, but remuxing is a little slower  
than copying the whole multi-gigabyte file - that takes a couple of  
minutes around here. To transcode a full DVD to highest quality h264  
might take 18 or 24 hours (on a Pentium 4).

As far as containers as concerned, .mp4 is a pretty good one. I  
_think_ that .m4v is very similar, but I can't swear to it. .avi is  
rubbish, but it's the default interim container for some converters -  
I think that mplayer / mencoder, for instance can produce technically  
invalid .avi files that won't play on some systems, but it does that  
because it assumes you know what you're doing and will remux them  
to .mp4 afterwards (using mp4box, for instance). .mkv is a container  
that is becoming very popular because it supports modern codes like  
h264/AAC but allows you to store multiple tracks within the container  
- Dolby stereo audio, 5.1 audio and a director's commentary, for  
instance, each of which may be in whatever codec you like. There is a  
shortcoming of of .mkv which applies to older systems with slower  
disks, but probably shouldn't apply here; if you can, use .mkv.

I believe you should try using this command on the file:

    mplayer -vo null -ao null -identify -endpos 1 myfile.m4v

This should tell you more about the codecs in which the content are  
encoded. Feel free to post the output here.

You didn't show us what the output (or verbose output) of your ffmpeg  
command was, so we don't know if the original .m4v had shitty quality,  
or if you transcoded it.

It's also worth checking the USE flags for all your video-playing  
applications - I enable at least the aac, h264 and mp3 USE flags on  
any new system, but I think Gentoo ships with them disabled by default  
because of licensing / patent / Freedom issues in some major  
jurisdictions.

HTH,

Stroller.