make fate not running all tests?make fate not finding the samples?Because no one has taken on that task yet. Libav development is driven by the tasks that are important to the individual developers. If there is a feature that is important to you, the best way to get it implemented is to undertake the task yourself or sponsor a developer.
No. Windows DLLs are not portable, bloated and often slow. Moreover Libav strives to support all codecs natively. A DLL loader is not conducive to that goal.
Even if avconv can read the container format, it may not support all its codecs. Please consult the supported codec list in the avconv documentation.
Windows does not support standard formats like MPEG very well, unless you install some additional codecs.
The following list of video codecs should work on most Windows systems:
.avi/.asf
.asf only
.asf only
.asf only
Only if you have some MPEG-4 codec like ffdshow or Xvid installed.
.mpg only
Note, ASF files often have .wmv or .wma extensions in Windows. It should also be mentioned that Microsoft claims a patent on the ASF format, and may sue or threaten users who create ASF files with non-Microsoft software. It is strongly advised to avoid ASF where possible.
The following list of audio codecs should work on most Windows systems:
always
If some MP3 codec like LAME is installed.
error: can't find a register in class 'GENERAL_REGS' while reloading 'asm'This is a bug in gcc. Do not report it to us. Instead, please report it to the gcc developers. Note that we will not add workarounds for gcc bugs.
Also note that (some of) the gcc developers believe this is not a bug or not a bug they should fix: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11203. Then again, some of them do not know the difference between an undecidable problem and an NP-hard problem...
First, rename your pictures to follow a numerical sequence. For example, img1.jpg, img2.jpg, img3.jpg,... Then you may run:
avconv -f image2 -i img%d.jpg /tmp/a.mpg |
Notice that ‘%d’ is replaced by the image number.
‘img%03d.jpg’ means the sequence ‘img001.jpg’, ‘img002.jpg’, etc...
If you have large number of pictures to rename, you can use the
following command to ease the burden. The command, using the bourne
shell syntax, symbolically links all files in the current directory
that match *jpg to the ‘/tmp’ directory in the sequence of
‘img001.jpg’, ‘img002.jpg’ and so on.
x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done |
If you want to sequence them by oldest modified first, substitute
$(ls -r -t *jpg) in place of *jpg.
Then run:
avconv -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg |
The same logic is used for any image format that avconv reads.
Use:
avconv -i movie.mpg movie%d.jpg |
The ‘movie.mpg’ used as input will be converted to ‘movie1.jpg’, ‘movie2.jpg’, etc...
Instead of relying on file format self-recognition, you may also use
to force the encoding.
Applying that to the previous example:
avconv -i movie.mpg -f image2 -c:v mjpeg menu%d.jpg |
Beware that there is no "jpeg" codec. Use "mjpeg" instead.
For multithreaded MPEG* encoding, the encoded slices must be independent, otherwise thread n would practically have to wait for n-1 to finish, so it’s quite logical that there is a small reduction of quality. This is not a bug.
Use ‘-’ as file name.
Try ’-f image2 test%d.jpg’.
Some codecs, like MPEG-1/2, only allow a small number of fixed framerates. Choose a different codec with the -c:v command line option.
Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4 standard (note that there are many other coding formats that use this same standard). Thus, use ’-c:v mpeg4’ to encode in these formats. The default fourcc stored in an MPEG-4-coded file will be ’FMP4’. If you want a different fourcc, use the ’-vtag’ option. E.g., ’-vtag xvid’ will force the fourcc ’xvid’ to be stored as the video fourcc rather than the default.
’-mbd rd -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -g 300 -pass 1/2’, things to try: ’-bf 2’, ’-flags qprd’, ’-flags mv0’, ’-flags skiprd’.
’-mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 100 -pass 1/2’ but beware the ’-g 100’ might cause problems with some decoders. Things to try: ’-bf 2’, ’-flags qprd’, ’-flags mv0’, ’-flags skiprd.
You should use ’-flags +ilme+ildct’ and maybe ’-flags +alt’ for interlaced material, and try ’-top 0/1’ if the result looks really messed-up.
If you have built Libav with ./configure --enable-avisynth
(only possible on MinGW/Cygwin platforms),
then you may use any file that DirectShow can read as input.
Just create an "input.avs" text file with this single line ...
DirectShowSource("C:\path to your file\yourfile.asf")
|
... and then feed that text file to avconv:
avconv -i input.avs |
For ANY other help on AviSynth, please visit the AviSynth homepage.
A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by merely concatenating them.
Hence you may concatenate your multimedia files by first transcoding them to
these privileged formats, then using the humble cat command (or the
equally humble copy under Windows), and finally transcoding back to your
format of choice.
avconv -i input1.avi intermediate1.mpg avconv -i input2.avi intermediate2.mpg cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg avconv -i intermediate_all.mpg output.avi |
Notice that you should set a reasonably high bitrate for your intermediate and output files, if you want to preserve video quality.
Also notice that you may avoid the huge intermediate files by taking advantage of named pipes, should your platform support it:
mkfifo intermediate1.mpg mkfifo intermediate2.mpg avconv -i input1.avi -y intermediate1.mpg < /dev/null & avconv -i input2.avi -y intermediate2.mpg < /dev/null & cat intermediate1.mpg intermediate2.mpg |\ avconv -f mpeg -i - -c:v mpeg4 -acodec libmp3lame output.avi |
Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also
allow concatenation, and the transcoding step is almost lossless.
When using multiple yuv4mpegpipe(s), the first line needs to be discarded
from all but the first stream. This can be accomplished by piping through
tail as seen below. Note that when piping through tail you
must use command grouping, { ;}, to background properly.
For example, let’s say we want to join two FLV files into an output.flv file:
mkfifo temp1.a
mkfifo temp1.v
mkfifo temp2.a
mkfifo temp2.v
mkfifo all.a
mkfifo all.v
avconv -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
avconv -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null &
avconv -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null &
{ avconv -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; } &
cat temp1.a temp2.a > all.a &
cat temp1.v temp2.v > all.v &
avconv -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
-f yuv4mpegpipe -i all.v \
-y output.flv
rm temp[12].[av] all.[av]
|
avconv prints an error like
Undefined constant or missing '(' in 'baseline'
Unable to parse option value "baseline"
Error setting option profile to value baseline.
|
Short answer: write ‘-profile:v’ instead of ‘-profile’.
Long answer: this happens because the ‘-profile’ option can apply to both video and audio. Specifically the AAC encoder also defines some profiles, none of which are named baseline.
The solution is to apply the ‘-profile’ option to the video stream only
by using Stream specifiers.
Appending :v to it will do exactly that.
Yes. Read the Developers Guide of the Libav documentation. Alternatively, examine the source code for one of the many open source projects that already incorporate Libav at (projects.html).
It depends. If your compiler is C99-compliant, then patches to support
it are likely to be welcome if they do not pollute the source code
with #ifdefs related to the compiler.
Yes. Please see the Microsoft Visual C++ section in the Libav documentation.
No. These tools are too bloated and they complicate the build.
Libav is already organized in a highly modular manner and does not need to be rewritten in a formal object language. Further, many of the developers favor straight C; it works for them. For more arguments on this matter, read "Programming Religion".
Yes, as long as the code is optional and can easily and cleanly be placed under #if CONFIG_GPL without breaking anything. So for example a new codec or filter would be OK under GPL while a bug fix to LGPL code would not.
Libav is a pure C project, so to use the libraries within your C++ application
you need to explicitly state that you are using a C library. You can do this by
encompassing your Libav includes using extern "C".
See http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3
Libav is a pure C project using C99 math features, in order to enable C++ to use them you have to append -D__STDC_CONSTANT_MACROS to your CXXFLAGS
You have to create a custom AVIOContext using avio_alloc_context,
see ‘libavformat/aviobuf.c’ in Libav and ‘libmpdemux/demux_lavf.c’ in MPlayer2 sources.
make fate not running all tests?Make sure you have the fate-suite samples and the SAMPLES Make variable
or FATE_SAMPLES environment variable or the --samples
configure option is set to the right path.
make fate not finding the samples?Do you happen to have a ~ character in the samples path to indicate a
home directory? The value is used in ways where the shell cannot expand it,
causing FATE to not find files. Just replace ~ by the full path.