Re: [gentoo-user] 4gb mpeg to 100mb xvid?

[Nick Rout <nick@rout.co.nz>]

On Wed, 7 Sep 2005 18:30:34 -0300 (ART)
Arturo 'Buanzo' Busleiman wrote:

> On Wed, 7 Sep 2005, Holly Bostick wrote:
> 
> > Rar or Tar.gz or zip the file up and share it, or encode it down to an
> > xvid (which will likely reduce the size at least somewhat, but anybody
> > correct me if I'm wrong) and *then* rar/tar.gz/zip it up and share it.
> 
> And how do I easily encode it down to an xvid?

your sample file shows the following with mplayer -identify:

ASF file format detected.
ID_AUDIO_ID=1
ID_VIDEO_ID=2
VIDEO:  [WMV3]  320x240  24bpp  1000.000 fps    0.0 kbps ( 0.0 kbyte/s)
==========================================================================
Opening audio decoder: [ffmpeg] FFmpeg/libavcodec audio decoders
AUDIO: 32000 Hz, 2 ch, s16le, 32.0 kbit/3.12% (ratio: 4000->128000)
Selected audio codec: [ffwmav2] afm:ffmpeg (DivX audio v2 (FFmpeg))
==========================================================================
ID_FILENAME=dd24_2005.wmv
ID_VIDEO_FORMAT=WMV3
ID_VIDEO_BITRATE=0
ID_VIDEO_WIDTH=320
ID_VIDEO_HEIGHT=240
ID_VIDEO_FPS=1000.000
ID_VIDEO_ASPECT=0.0000
ID_AUDIO_CODEC=ffwmav2
ID_AUDIO_FORMAT=353
ID_AUDIO_BITRATE=32000
ID_AUDIO_RATE=32000
ID_AUDIO_NCH=2
ID_LENGTH=3232
==========================================================================
Opening video decoder: [dmo] DMO video codecs
DMO dll supports VO Optimizations 0 1
DMO dll might use previous sample when requested
GetOutput r=0x0   size:230400  align:1
StreamCount r=0x0  1  1
Decoder supports the following YUV formats: YV12 YUY2 UYVY YVYU
Decoder is capable of YUV output (flags 0x1b)
VDec: vo config request - 320 x 240 (preferred csp: Packed YUY2)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is undefined - no prescaling applied.
VO: [null] 320x240 => 320x240 Planar YV12
Selected video codec: [wmv9dmo] vfm:dmo (Windows Media Video 9 DMO)
==========================================================================
Checking audio filter chain for 32000Hz/2ch/s16le -> 32000Hz/2ch/s16le...
AF_pre: 32000Hz/2ch/s16le
alsa-init: 1 soundcard found, using: default
alsa: 32000 Hz/2 channels/4 bpf/43688 bytes buffer/Signed 16 bit Little Endian
AO: [alsa] 32000Hz 2ch s16le (2 bps)
Building audio filter chain for 32000Hz/2ch/s16le -> 32000Hz/2ch/s16le...
Starting playback...


Clearly the frames per second is misreported at 1000 (this seems a
common problem with wmv files and ffmpeg/mplayer). However you can see
that it has been coded down to 320x240 pixels.

It is remarkably watchable, albeit I don't understand the language. Yu
can use the above parameters to re-encode it with a variety of tools,
you will have to do a little research as to what will work best. It will take a bit of cpu processing too!

The possible tools are:

ffmpeg
mencoder (part of mplayer)
transcode

The common approach is to separate the audio and video channels,
re-encode each of them to the required bitrate and size, and then mplex
them back together again. There is no one tool or "right" approach.
There is a lot of reading to do. 

avidemux does provide a gui which may be useful - it helps set up
parameters for the various formats and ocdecs. It uses the same basic
tools "under the hood" though.

For a reasonably well documented script that does a similar thing, and
may provide inspiration, see http://forums.gentoo.org/viewtopic.php?t=117709&highlight=codecs

(this documents any2vob, which takes any old video file and converts it
to a format suitable for burning to dvd. You are doing pretty much the
opposite, but the steps and tools are the same.)

> 
> --
> Buanzo
> 
> -- 
> gentoo-user@gentoo.org mailing list

-- 
Nick Rout <nick@rout.co.nz>

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