@section How can I join video files?
-A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by
-merely concatenating them.
+To "join" video files is quite ambiguous. The following list explains the
+different kinds of "joining" and points out how those are addressed in
+FFmpeg. To join video files may mean:
+
+@itemize
+
+@item
+To put them one after the other: this is called to @emph{concatenate} them
+(in short: concat) and is addressed
+@ref{How can I concatenate video files, in this very faq}.
+
+@item
+To put them together in the same file, to let the user choose between the
+different versions (example: different audio languages): this is called to
+@emph{multiplex} them together (in short: mux), and is done by simply
+invoking ffmpeg with several @option{-i} options.
+
+@item
+For audio, to put all channels together in a single stream (example: two
+mono streams into one stereo stream): this is sometimes called to
+@emph{merge} them, and can be done using the
+@url{http://ffmpeg.org/ffmpeg.html#amerge, @code{amerge}} filter.
+
+@item
+For audio, to play one on top of the other: this is called to @emph{mix}
+them, and can be done by first merging them into a single stream and then
+using the @url{http://ffmpeg.org/ffmpeg.html#pan, @code{pan}} filter to mix
+the channels at will.
+
+@item
+For video, to display both together, side by side or one on top of a part of
+the other; it can be done using the
+@url{http://ffmpeg.org/ffmpeg.html#overlay, @code{overlay}} video filter.
+
+@end itemize
+
+@anchor{How can I concatenate video files}
+@section How can I concatenate video files?
+
+There are several solutions, depending on the exact circumstances.
+
+@subsection Concatenating using filters
+
+FFmpeg has a @url{http://ffmpeg.org/ffmpeg.html#concat-1, @code{concat}}
+filter designed specifically for that, with examples in the documentation.
+
+@subsection Concatenating at the file level
+
+A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to concatenate
+video by merely concatenating the files them.
Hence you may concatenate your multimedia files by first transcoding them to
these privileged formats, then using the humble @code{cat} command (or the
format of choice.
@example
-ffmpeg -i input1.avi -same_quant intermediate1.mpg
-ffmpeg -i input2.avi -same_quant intermediate2.mpg
+ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg
+ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg
cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
-ffmpeg -i intermediate_all.mpg -same_quant output.avi
+ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi
@end example
-Notice that you should either use @code{-same_quant} or set a reasonably high
-bitrate for your intermediate and output files, if you want to preserve
-video quality.
+Additionally, you can use the @code{concat} protocol instead of @code{cat} or
+@code{copy} which will avoid creation of a potentially huge intermediate file.
-Also notice that you may avoid the huge intermediate files by taking advantage
-of named pipes, should your platform support it:
+@example
+ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg
+ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg
+ffmpeg -i concat:"intermediate1.mpg|intermediate2.mpg" -c copy intermediate_all.mpg
+ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi
+@end example
+
+Note that you may need to escape the character "|" which is special for many
+shells.
+
+Another option is usage of named pipes, should your platform support it:
@example
mkfifo intermediate1.mpg
mkfifo intermediate2.mpg
-ffmpeg -i input1.avi -same_quant -y intermediate1.mpg < /dev/null &
-ffmpeg -i input2.avi -same_quant -y intermediate2.mpg < /dev/null &
+ffmpeg -i input1.avi -qscale:v 1 -y intermediate1.mpg < /dev/null &
+ffmpeg -i input2.avi -qscale:v 1 -y intermediate2.mpg < /dev/null &
cat intermediate1.mpg intermediate2.mpg |\
-ffmpeg -f mpeg -i - -same_quant -c:v mpeg4 -acodec libmp3lame output.avi
+ffmpeg -f mpeg -i - -qscale:v 2 -c:v mpeg4 -acodec libmp3lame -q:a 4 output.avi
@end example
+@subsection Concatenating using raw audio and video
+
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
@code{tail} as seen below. Note that when piping through @code{tail} you
must use command grouping, @code{@{ ;@}}, to background properly.
-For example, let's say we want to join two FLV files into an output.flv file:
+For example, let's say we want to concatenate two FLV files into an
+output.flv file:
@example
mkfifo temp1.a
cat temp1.v temp2.v > all.v &
ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
-f yuv4mpegpipe -i all.v \
- -same_quant -y output.flv
+ -qscale:v 2 -y output.flv
rm temp[12].[av] all.[av]
@end example
aconvert=s16:stereo:packed
@end example
+@section Why does FFmpeg not see the subtitles in my VOB file?
+
+VOB and a few other formats do not have a global header that describes
+everything present in the file. Instead, applications are supposed to scan
+the file to see what it contains. Since VOB files are frequently large, only
+the beginning is scanned. If the subtitles happen only later in the file,
+they will not be initally detected.
+
+Some applications, including the @code{ffmpeg} command-line tool, can only
+work with streams that were detected during the initial scan; streams that
+are detected later are ignored.
+
+The size of the initial scan is controlled by two options: @code{probesize}
+(default ~5 Mo) and @code{analyzeduration} (default 5,000,000 µs = 5 s). For
+the subtitle stream to be detected, both values must be large enough.
+
@chapter Development
@section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
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.
+@section I'm using FFmpeg from within my C application but the linker complains about missing symbols from the libraries themselves.
+
+FFmpeg builds static libraries by default. In static libraries, dependencies
+are not handled. That has two consequences. First, you must specify the
+libraries in dependency order: @code{-lavdevice} must come before
+@code{-lavformat}, @code{-lavutil} must come after everything else, etc.
+Second, external libraries that are used in FFmpeg have to be specified too.
+
+An easy way to get the full list of required libraries in dependency order
+is to use @code{pkg-config}.
+
+@example
+ c99 -o program program.c $(pkg-config --cflags --libs libavformat libavcodec)
+@end example
+
+See @file{doc/example/Makefile} and @file{doc/example/pc-uninstalled} for
+more details.
+
@section I'm using FFmpeg from within my C++ application but the linker complains about missing symbols which seem to be available.
FFmpeg is a pure C project, so to use the libraries within your C++ application
projects / ffmpeg / blobdiff