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.
