ffmpeg - piped input (from dvgrab) problem

Jerry L Bash · *nix forums beginner Joined: 04 Feb 2005 Posts: 2

Hi,

I need to capture analog video and convert to mpeg 'on the fly'. I am
trying to use hardware that I currently have, which includes a canopus
ADCV-100 capture device, and a PC running debian linux (sid). I need a
command line interface (or something that can be easily scripted, and I
discovered dvgrab and ffmpeg in my googling. Seemed like this should be
do-able, so I installed a 1394 capture card in the PC and began.
Initially, I installed the 2.6.10 kernel (a debian build), but found
(googling) that there were some problems with that (which I was
experiencing as well), so I reverted to a 2.4 kernel.

To date, I have been able to capture the video and store to a file:

dvgrab foo- (which stores .avi files in the default format (.avi) and the
default size (1GB) ...

I can view them (using vlc or xine) as well as convert these files to mpg
files without problems, as in:

ffmpeg -i foo-001.avi -target vcd foo-001.mpg

Again checking that the results are viewable from vlc and xine.

My final step (for now; before the next final step : ) ) is to pipe the
output of the dvgrab to ffmpeg to generate the mpg file. I was thinking
something along the lines of:

dvgrab - | ffmpeg -i - -target vcd foo-001.mpg

realizing I may have to adjust durations, etc. (I'm not sure how ffmpeg
will name the files, or for that matter, if dvgrab will split the files if
it is piping to stdout. It's a detail I'll have to work.)

However, this did not work. I get:

pipe:: Unknown format
Capture Started

(looks like the canopus starts to capture for 3 or 4 seconds, then
everything quits, and I'm back to a command prompt.

So, I try specifying the format:

dvgrab - | ffmpeg -f avi -i - -target vcd foo-001.mpg

but now, I get:

pipe: Error while opening file
Capture started

(same behavior from the canopus and command shell).

I then backed up and tried piping the output of the avi file I captured to
ffmpeg (again, from a command line, specifying '-i filename', all is
well).

cat foo-001.avi | ffmpeg -i - -target vcd foo-001.mpg

This command starts and finishes very quickly (too quickly). foo-001.mpg
is an empty file. No change if I specify the format (-f option) as above.

Just to check my syntax and procedure, I took the file I converted to mpg
(ffmpeg -i foo-001.avi -target vcd foo-001.mpg) and pipe it back through
ffmpeg:

cat foo-001.mpg | ffmpeg -i - -target dvd foo-001a.mpg

and find that this works fine.

I have tried other formats from dvgrab (dv1, dv2, raw, ...), and then
indicating that format for ffmpeg, but thusfar without success.

(Grasping for straws), I've also tried using a named pipe, not knowing
exactly how, but this is what I tried:

mkfifo vidbuff.avi
cat foo-001.avi > vidbuff.avi | ffmpeg -i - -target vcd foo-001.mpg

This just sits, as if it's waiting for input somewhere. There is probably
something wrong with my syntax here, but I'm not even sure it should be
needed.

(Potentially) Relevant additional information -

ffmpeg installation - from debian cvs20050121
dvgrab - debian package (1.7-1)

Here is an output from ffmpeg which indicates build information.

jlb@elm:~/capture/geo_20-21$ ffmpeg -i geo_2021-001.dv -target vcd
geo_2021-001.mpg
ffmpeg version 0.4.9-pre1, build 4738, Copyright (c) 2000-2004 Fabrice
Bellard
configuration: --build i386-linux --enable-gpl --enable-pp
--enable-zlib --enable-vorbis --enable-a52 --enable-dts --disable-mmx
--disable-debug --prefix=/usr
built on Jan 21 2005 19:24:19, gcc: 3.3.5 (Debian 1:3.3.5-6)

Any help you can provide would be greatly appreciated. From the posts I
have read, it seems like this should be a do-able thing. Initially I was
afraid the processor would not keep up, but it seems that ffmpeg is very
fast, as indicated in the posts, and confirmed by my tests (converting a
file is completed in less than real time (75% or so)), so it seems
reasonable. I know I may be able to use a hardware mpeg encoder, but I
like the flexibility the canopus device gives me.

Thanks in advance.
Jerry

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