Re: [transcode-users] Question about video preprocessing (contrast)and transcode

[Francesco Romani <fromani@xxxxxxxxx>]

On Sat, 29 Jul 2006 19:35:19 -0300
"Marlon Brandão de Sousa" <splyt.lists@xxxxxxxxx> wrote:

[...]
> I decided first to preprocess the contrast and brigtness in the avi
> file generating a pre processed avi file and after this encode the pre
> processed file into an 3gp one.

In order to preserve the maximum possible source qulity, I always recommend
to do the least amount of transcoding possible, so from my own modest
viewpoint the best strategy will be to 
1) transcode directly your source material into mpeg4-on-avi applying
corrections on the fly (transcode should be fine for this step)
2) translate mpeg4/avi into final format by just changing the container
(here ffmpeg could help since it supports way more containers, yet).

[...]
> There I read I need to know what codecs my avi file contains before
> trying to run transcode.

Well, transcode has some (fair) autodetection facilities that are
supposed to save users from this task :)
Anyway, to know what we're going to transcode isn't a bad idea :)

> tcprobe -i gol.avi
> [tcprobe] RIFF data, AVI video
> [avilib] V: 29.970 fps, codec=MJPG, frames=450, width=320, height=240
> [avilib] A: 48000 Hz, format=0x01, bits=16, channels=2, bitrate=1536 kbps,
> [avilib]    451 chunks, 2882880 bytes, CBR
> [tcprobe] summary for gol.avi, (*) = not default, 0 = not detected
> import frame size: -g 320x240 [720x576] (*)
>        frame rate: -f 29.970 [25.000] frc=4 (*)
>       audio track: -a 0 [0] -e 48000,16,2 [48000,16,2] -n 0x1 [0x2000] (*)
>                    bitrate=1536 kbps
>            length: 450 frames, frame_time=33 msec,
> duration=0:00:15.015
> 
> The strange thing is that it didnt show the audio codec used in the
> .avi file.

It shows, but in a cryptic form (yeah, this should be improved too).
See the third line of output, the format=XXX field. Here we have a PCM audio
track (no encoded): 0x01 -> PCM

> Ok, now I know my video is mjpg and audio is pcm. So what I want is to
> generate another .avi file, with the same size, with mjpg and audio
> pcm, with the same size, etc ... with contrast and brightness changed.

OK, there is some options and filters that hopefully could help you
-G, pp filter, yuvdenoise filter, maybe xsharpen filter too.

Warning: all filter above are VERY cpu-hungry.

Hope This Helps,

Best regards

-- 
Francesco Romani - Ikitt ['people always complain, no matther what you do']
IM contact    : (email first, Antispam default deny!) icq://27-83-87-867
known bugs    : http://www.transcoding.org/cgi-bin/transcode?Bug_Showcase
tiny homepage : http://fromani.exit1.org (see IDEAS if you want send code!)