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• How to capture screenshots from a video clip 50 minutes into the clip and do it fast ?

  3 janvier 2015, par Mint

  Ok it seems that whenever I tell ffmpeg to take a screen cap half way though the clip (clip can be as long as 10 hours) it uses 100% of 1 cpu core and takes ages… whereas if I let it do a frame at the start it goes real quick, as if it scans though the video to get to the middle instead of just jumping to it !

  Here is the code im currently using :

  ffmpeg -y -itsoffset -“500"  -i “clipname.mov" -vcodec png -vframes 1 -an -f rawvideo “clipScreenshot001.png”

  This can take several minutes.

  These are HD videos too, 720p/1080p and allot of the time they are raw unedited clips (e.g. very long).

  So I was hoping for some better software that will make screen captures from video much faster (has to be linux and scriptable).

• Using ffmpeg with C++ : Undefined symbols for architecture x86_64

  31 mars 2017, par JavaRunner

  I’m dealing with one example of FFMPEG called is "muxing.c".

  So I tried to compile that file with two Makefiles. The first one is for C-language :

  FFMPEG_LIBS=    libavdevice                        \
  
                  libavformat                        \
  
                  libavfilter                        \
  
                  libavcodec                         \
  
                  libswresample                      \
  
                  libswscale                         \
  
                  libavutil                          \
  
  
  
  CFLAGS := -Wall -g $(shell pkg-config --cflags $(FFMPEG_LIBS)) $(CFLAGS)
  
  LDLIBS := $(shell pkg-config --libs $(FFMPEG_LIBS)) -lm $(LDLIBS)
  
  
  
  SOURCES=        muxing                             \
  
  
  
  OBJS=$(addsuffix .o,$(SOURCES))
  
  
  
  all: $(OBJS) $(SOURCES)

  That makefile compiles well. But if I trying to move this code to C++ : I rename muxing.c to muxing.cpp and use this Makefile :

  CC=g++
  
  
  
  FFMPEG_LIBS=    libavdevice                        \
  
                  libavformat                        \
  
                  libavfilter                        \
  
                  libavcodec                         \
  
                  libswresample                      \
  
                  libswscale                         \
  
                  libavutil                          \
  
  
  
  CPPFLAGS := -Wall -g $(shell pkg-config --cflags $(FFMPEG_LIBS)) $(CPPFLAGS)
  
  LDLIBS := $(shell pkg-config --libs $(FFMPEG_LIBS)) -lm $(LDLIBS)
  
  
  
  SOURCES=        muxing                             \
  
  
  
  OBJS=$(addsuffix .o,$(SOURCES))
  
  
  
  all: $(OBJS) $(SOURCES)

  I get a bunch of error like this :

  $ g++   muxing.o  -L/usr/local/Cellar/ffmpeg/3.2.4/lib -lavdevice -lavformat -lavfilter -lavcodec -lswresample -lswscale -lavutil  -lm -o muxing
  
  Undefined symbols for architecture x86_64:
  
    "av_dict_set(AVDictionary**, char const*, char const*, int)", referenced from:
  
        _main in muxing.o
  
    "av_strerror(int, char*, unsigned long)", referenced from:
  
        av_make_error_string(char*, unsigned long, int) in muxing.o
  
    "avio_closep(AVIOContext**)", referenced from:
  
        _main in muxing.o
  
    "swr_convert(SwrContext*, unsigned char**, int, unsigned char const**, int)", referenced from:
  
        write_audio_frame(AVFormatContext*, OutputStream*) in muxing.o
  
    "av_dict_copy(AVDictionary**, AVDictionary const*, int)", referenced from:
  
        open_video(AVFormatContext*, AVCodec*, OutputStream*, AVDictionary*) in muxing.o
  
        open_audio(AVFormatContext*, AVCodec*, OutputStream*, AVDictionary*) in muxing.o
  
    "av_dict_free(AVDictionary**)", referenced from:
  
        open_video(AVFormatContext*, AVCodec*, OutputStream*, AVDictionary*) in muxing.o
  
        open_audio(AVFormatContext*, AVCodec*, OutputStream*, AVDictionary*) in muxing.o
  
    "av_rescale_q(long long, AVRational, AVRational)", referenced from:
  
        write_audio_frame(AVFormatContext*, OutputStream*) in muxing.o
  
    "av_compare_ts(long long, AVRational, long long, AVRational)", referenced from:
  
        _main in muxing.o
  
        get_video_frame(OutputStream*) in muxing.o
  
        get_audio_frame(OutputStream*) in muxing.o

  Is that mean those libs are not ready to work with x64 ? I strongly need to mix that code (muxing.c) with my C++ code because I have to render a video on the fly using ImageMagick (my code was written with C++) for the frames.

  How can I mix C++ and C in this case ?

  My env is : OS X 10.12.3

• Combining Video and Audio of different length in bulk

  25 mai 2017, par user2981223

  I am going through a tv series right now and editing the files to be to my liking. I have one set which has the video I want and one set that has the audio. I have a batch file that I can run that takes the video from every file in folder "A" and the audio from every file in folder "B" and outputs it to a folder named "output." But with this particular series, that is only half of what I need done.

  At the end of every episode of the files in the "B" folder there are some extra things. What I would like to do is take the audio and video from "A" and the audio from "B", combine it all into one file and also take the "A" and "B" files, compare the time stamps, and add the extra video from "B" to the output file.

  Let me put it another way. Let’s say "A" is 1080p with Japanese audio and is 20 minutes long. Let’s say "B" is 720p with English audio and is 23 minutes long. I want the whole 1080p video with both audio tracks, plus the 720p video spliced onto the end. Both files start at the same spot so syncing isn’t an issue. The issue is that the difference in time is different for every episode. So some episodes are 3 minutes longer, some only 30 seconds. Is there a way to make ffmpeg or another tool look at the difference in times and just add the excess to the output file ?

  Sorry for being long winded. Thanks for any help and guidance.