[Haifux] Re: Re: [Haifux] Encoding internet-quality video

Fri, 21 May 2004 01:42:27 -0700

Hello ,
 
  You were wrong in some of your assumptions.
 
I do indeed work with 352x288 (CIF) size , but I grab it from
a WebCam (and not from PAL).
 
The duration is 10 seconds , in the frame rate is 10 fps ; so
totally we have 100 frames.
 
The ffmpeg displays a report line at the end of its action.
This line includes important statistics like bitframe, size,time,etc.
 
I repeated this morning this process ;
The only difference is that I grabbed directly to a yuv file and not to an AVI file
in the first step, which is really unimportant.
Here is exactly  what I did  , includeng ffmpeg reoprt lines:
(there are little difference n the size of the encoded file comparing to yesterday data  ; these are due
to doing less motion in front of the camera while grabbing.
 
 
1)
===============
../ffmpeg -y -t 10 -r 10 -s cif -vd /dev/video0 in.yuv
 
grabs frames from a webcam and creates in.yuv of size 15206400 Bytes
report line:
 frame=  100 q=0.0 Lsize=   14850kB time=10.0 bitrate=12165.1kbits/s
=============================
2)
 ../ffmpeg -y -t 10 -r 10 -s cif -vcodec h263 -i in.yuv in263.yuv
 craetes in263.yuv of size 371004 byes
 
report line:
 frame=  100 q=1.7 Lsize=     362kB time=10.0 bitrate= 296.8kbits/s
video:362kB audio:0kB global headers:0kB muxing overhead 0.000000%
 =============================
3)
../ffmpeg -y -t 10 -r 10 -s cif -i in263.yuv out263.yuv
 
creates out263.yuv of size 15054336 Bytes
 
frame=   99 q=0.0 Lsize=   14702kB time=3.3 bitrate=36458.9kbits/s
video:14702kB audio:0kB global headers:0kB muxing overhead 0.000000%

=============================
.4)
../ffmpeg -y -t 10 -r 10 -s cif -i out263.yuv out263.avi
 
creates  out263.avi of size 302446
 
 
you can play the file with vlc or mplayer - as I said , I got quite good results
 
From what I understand , the codecs you should use are not h263/h263plus
(which are more proper for video conference apps; gnomemeeting uses them, for example)
but mpeg codecs.
 
regarding vlc - it is primarily a streaming tool which has many codecs libraries
(including ffmpeg ; if you build it from source you can add some others).
you can also grab with it from a webcam if you build it with enable video4linux.
 
and BTW , it happens to me more than once that it played files where other players
failed.
 
 
Hope this clears things up.
 
regards
Rami Rosen
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Eli Billauer wrote: > Hello, and thanks again.

I just want to get things in order:
You can also try viodeolan
After viewing their site, I'm under the impression that it's a (cool)streaming tool, with no encoding capabilities of its own. It usestranscode to do the job for it (or am I wrong?).

Anyhow, it's interesting in itself.
Second , I do not know what your final goal is , but if you want
to save the file in a compressed format,
Exactly. A small compressed file to put on a website.

As for your example, let me make a few guesses. Tell me if I got itwrong:
and I worked with CIF (352x288) window size.

Bytes

the size of the  yuv420p :             15206400 Bytes

the size ofthe encoded h263 file:     384647Bytes (which is about 0.025 of the yuv file)
the size ofthe decoded h263 file: 15054336 Bytes
 
My guess: 75 frames of 352x288 pixels, with each YUV pixel occupying 2bytes on the average (due to U & V downsampling), so we have:

75 * 352 * 288 * 2 = 15206400 bytes. You ran 25 frames per second(grabbed from PAL, I suppose) so that's 3 seconds of video.

Bitrate: 384647 *8 = 3077176 bits, divided by 3 seconds, we have grossly 1 Mbit/sec.Which is more or less like VCD. No wonder you got great results.


But I want the low-quality thingy!

Thanks anyhow,
    Eli

-- Web: http://www.billauer.co.il






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