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• Trouble linking ffmpeg example source code

  30 janvier 2012, par Leonard Teo

  I managed to build ffmpeg and libx264 on my Ubuntu 11.10 machine from source.

  I'm trying to work on the example source file decoding_encoding.c. The examples comes with a makefile, so I can just type in "make all" and it magically compiles and links everything. Now, I'm trying to compile and link from the command line but I can't seem to get it to link.

  Here is the makefile :

  # use pkg-config for getting CFLAGS abd LDFLAGS
  
  FFMPEG_LIBS=libavdevice libavformat libavfilter libavcodec libswscale libavutil
  
  CFLAGS+=$(shell pkg-config  --cflags $(FFMPEG_LIBS))
  
  LDFLAGS+=$(shell pkg-config --libs $(FFMPEG_LIBS))
  
  
  
  EXAMPLES=decoding_encoding filtering metadata muxing
  
  
  
  OBJS=$(addsuffix .o,$(EXAMPLES))
  
  
  
  %: %.o
  
          $(CC) $< $(LDFLAGS) -o $@
  
  
  
  %.o: %.c
  
          $(CC) $< $(CFLAGS) -c -o $@
  
  
  
  .phony: all clean
  
  
  
  all: $(OBJS) $(EXAMPLES)
  
  
  
  clean:
  
          rm -rf $(EXAMPLES) $(OBJS)

  I can compile the source using this :

  gcc -Wall -I/usr/local/include -c -o decoding_encoding.o decoding_encoding.c

  When I try to link using this :

  gcc -Wall -L/usr/local/lib -lavdevice -lavformat -lavfilter -lavcodec -lswscale -lavutil -o decoding_encoding decoding_encoding.o

  At this point, I get a huge list of 'undefined reference error'

  decoding_encoding.o: In function `audio_encode_example':
  
  decoding_encoding.c:(.text+0x25): undefined reference to `avcodec_find_encoder'
  
  decoding_encoding.c:(.text+0x6a): undefined reference to `avcodec_alloc_context3'
  
  decoding_encoding.c:(.text+0xad): undefined reference to `avcodec_open'
  
  decoding_encoding.c:(.text+0x1ce): undefined reference to `sin'
  
  decoding_encoding.c:(.text+0x238): undefined reference to `avcodec_encode_audio'
  
  decoding_encoding.c:(.text+0x297): undefined reference to `avcodec_close'
  
  decoding_encoding.c:(.text+0x2a3): undefined reference to `av_free'
  
  decoding_encoding.o: In function `audio_decode_example':
  
  decoding_encoding.c:(.text+0x2f7): undefined reference to `av_init_packet'
  
  decoding_encoding.c:(.text+0x30b): undefined reference to `avcodec_find_decoder'
  
  decoding_encoding.c:(.text+0x359): undefined reference to `avcodec_alloc_context3'
  
  decoding_encoding.c:(.text+0x379): undefined reference to `avcodec_open'
  
  ..... etc.
  
  collect2: ld returned 1 exit status

  Am I doing something wrong with my linker command ? I've examined the makefile and I believe that I'm doing exactly what the makefile is....or am I ?

  Thanks,

  Leo

• FFmpeg : how to use C++ code to change the frame rate of a video file ?

  27 mars 2014, par user1914692

  I know it would be easier to use FFmpeg commands to change the frame rate of a video file.
  But anyway, if I want to do it in C++ code, and use FFmpeg libraries, how could I do it ?

  I think I should've be able to find out the clue in the source code.
  Just before proceeding, I hope there would be some good introductions or examples.

• ffmpeg combine audio mix code into complex concate script

  15 mai 2020, par sisterbrother

  I got currently 2 different ffmpeg scripts which I want to combine. I do not have good ffmpeg experience and those codes are mostly googel code so please be patient with me

  



  The first code is concating 3 videos :

  



  ffmpeg -y -i "$vid1" -i "$fp" -i "$vid1" -filter_complex \
"[0:v]scale=$cResolution:force_original_aspect_ratio=decrease,pad=$cResolution:(ow-iw)/2:(oh-ih)/2,setsar=1,fps=30,format=yuv420p[v0]; \
 [1:v]scale=$cResolution:force_original_aspect_ratio=decrease,pad=$cResolution:(ow-iw)/2:(oh-ih)/2,setsar=1,fps=30,format=yuv420p[v1]; \
 [2:v]scale=$cResolution:force_original_aspect_ratio=decrease,pad=$cResolution:(ow-iw)/2:(oh-ih)/2,setsar=1,fps=30,format=yuv420p[v2]; \
 [0:a]aformat=sample_rates=48000:channel_layouts=stereo[a0]; \
 [1:a]aformat=sample_rates=48000:channel_layouts=stereo[a1]; \
 [2:a]aformat=sample_rates=48000:channel_layouts=stereo[a2]; \
 [v0][a0][v1][a1][v2][a2]concat=n=3:v=1:a=1[v][a]; \
 [v]drawtext=text='example..':y=h-line_h-$h3:x=w/30*mod(t\,20):enable='gt(mod(t,$dr2),$Introdr_rounded)'[v]; \
 [v]drawtext=text='example..':y=h-line_h-$hcentral:x=w/20*mod(t\,100):enable='gt(mod(t,$dr2),$Introdr_rounded)'[v]; \
 [v]drawtext=text='example..':y=h-line_h-23:x=w/30*mod(t\,20):enable='gt(mod(t,$dr2),$Introdr_rounded)'[v]" \
 -map "[v]" -map "[a]" -c:v libx264 -crf 22 -preset veryfast -c:a aac -movflags +faststart "$fp_dest"


  



  The second code is overlay a background mp3 in endless loop to the created video from above. Its important to know that this code does overlap the audio of the video and does not replace it. In future I will lower the volume of the mp3 files to work as background music

  



  ffmpeg -y -i "$fp_dest" -filter_complex "amovie=$audio:loop=0,asetpts=N/SR/TB[aud];[0:a][aud]amix[a]" -map 0:v -map '[a]' -c:v copy -c:a aac -b:a 256k -shortest ./test.mp4



  



  So currently I got 2 steps which I want to combine into 1 step. Can you please help me to include the second code into the first one without change any logic of the code ?