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• Crossfade many audio files into one with FFmpeg ?

  3 octobre 2018, par setouk

  Using FFmpeg, I am trying to combine many audio files into one long one, with a crossfade between each of them. To keep the numbers simple, let’s say I have 10 input files, each 5 minutes, and I want a 10 second crossfade between each. (Resulting duration would be 48:30.) Assume all input files have the same codec/bitrate.

  I was pleasantly surprises to find how simple it was to crossfade two files :

  ffmpeg -i 0.mp3 -i 1.mp3 -vn -filter_complex acrossfade=d=10:c1=tri:c2=tri out.mp3

  But the acrossfade filter does not allow 3+ inputs. So my naive solution is to repeatedly run ffmpeg, crossfading the previous intermediate output with the next input file. It’s not ideal. It leads me to two questions :

  1. Does acrossfade losslessly copy the streams ? (Except where they’re actively crossfading, of course.) Or do the entire input streams get reencoded ?

  If the input streams are entirely reencoded, then my naive approach is very bad. In the example above (calling acrossfade 9 times), the first 4:50 of the first file would be reencoded 9 times ! If I’m combining 50 files, the first file gets reencoded 49 times !

  2. To avoid multiple runs and the reencoding issue, can I achieve the many-crossfade behavior in a single ffmpeg call ?

  I imagine I would need some long filtergraph, but I haven’t figured it out yet. Does anyone have an example of crossfading just 3 input files ? From that I could automate the filtergraphs for longer chains.

  Thanks for any tips !

• Trimming video without encoding

  14 octobre 2020, par Cristian Jorge A. Kusch

  I need to trim a video without encoding into sections that later i can put back together with the concat demuxer of ffmpeg.
I understand that to cut precisely without encoding it is necessary to cut at keyframes, i'm using this command to get the keyframes :

  


  ffprobe -loglevel error -select_streams v:0 -show_entries packet=pts_time,flags -of csv=print_section=0 -input | awk -F',' '/K/ {print $1}'


  


  and they also correspond to the times that Avidemux reports for the keyframes.
I'm using this command to trim the source :

  


  ffmpeg -ss 00:0:2.4607 -noaccurate_seek -avoid_negative_ts 1 -i input.mp4 -to 00:0:3.545 -c copy /content/losslessffmpeg.mp4


  


  But it always ends up with different durations. I would expect that if i cut between keyframe at time 2.460792 and keyframe at time 3.545208 i would get a video of lenght that is the difference between those two times, but it is never the case.
Any help ?
thanks

  


• linker error in Android NDK r25c when cross-compiling FFmpeg

  5 août 2023, par Sai Chaithanya

  I am cross compiling FFmpeg for Android(aarch64) using Android NDK r25c on Linux x86_64 platform. The errors generated by the linker are because of enabling the LTO option.
  
On disabling the LTO options(--enable-lto optional config and -flto=thin cc-flag), there are no failures.

  


  FFmpeg config :

  


  ./configure --arch=aarch64 --target-os=android --enable-cross-compile --disable-everything \ 
 --disable-network --disable-autodetect --enable-small --disable-debug --disable-doc \ 
 --disable-manpages --disable-podpages --disable-txtpages --disable-htmlpages --disable-shared \
 --enable-static --enable-decoder='aac*,ac3*,opus,vorbis,mjpeg,mp3' \ 
 --enable-demuxer='mov,m4v,matroska,image2,mp3' --enable-protocol=file --enable-muxer='mp3,mp4,webm,null' \  
 --enable-libmp3lame --enable-encoder=libmp3lame --enable-filter=aresample --enable-logging \ 
 --enable-pthreads --enable-parser='vorbis,opus,vp8,vp9,mjpeg,h264,aac*,ac3*,mpegvideo,mpegaudio,mpeg4video' \
 --disable-ffprobe --disable-ffplay --prefix='$HOME/Downloads/custom_build' --enable-lto \
 --extra-cflags="-I$HOME/Downloads/custom_build/include -I$HOME/Downloads/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/include -O3 -flto=thin" \
 --extra-ldflags="-L$HOME/Downloads/custom_build/lib -L$HOME/Downloads/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/lib64" \
 --cc="aarch64-linux-android33-clang" --nm=llvm-nm --strip=llvm-strip


  


  Error :

  


  ld: error: undefined symbol: av_packet_alloc
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced 10 more times

ld: error: undefined symbol: av_usleep
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced by ld-temp.o
>>>               lto.tmp:(main)
>>> referenced by ld-temp.o
>>>               lto.tmp:(retry_transfer_wrapper)

ld: error: undefined symbol: av_log
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced 745 more times

ld: error: undefined symbol: av_thread_message_queue_send
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced 1 more times

ld: error: undefined symbol: av_thread_message_queue_recv
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced by ld-temp.o
>>>               lto.tmp:(main)
>>> referenced by ld-temp.o
>>>               lto.tmp:(ffmpeg_cleanup)

ld: error: undefined symbol: av_rescale_q
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced 62 more times

ld: error: undefined symbol: av_packet_move_ref
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced by ld-temp.o
>>>               lto.tmp:(submit_packet)
>>> referenced by ld-temp.o
>>>               lto.tmp:(pkt_move)
>>> referenced 3 more times

ld: error: undefined symbol: av_thread_message_queue_set_err_recv
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)

ld: error: undefined symbol: av_packet_free
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced by ld-temp.o
>>>               lto.tmp:(input_thread)
>>> referenced by ld-temp.o
>>>               lto.tmp:(mux_check_init)
>>> referenced 13 more times

ld: error: undefined symbol: av_compare_ts
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_duration_update)
>>> referenced by ld-temp.o
>>>               lto.tmp:(finish_stream)
>>> referenced by ld-temp.o
>>>               lto.tmp:(finish_stream)
>>> referenced 10 more times

ld: error: undefined symbol: av_dict_set_int
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(of_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(mov_read_ftyp)
>>> referenced 1 more times

ld: error: undefined symbol: av_dict_get
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(configure_filtergraph)
>>> referenced by ld-temp.o
>>>               lto.tmp:(main)
>>> referenced 25 more times

ld: error: undefined symbol: av_opt_set_dict
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(init_output_stream_wrapper)
>>> referenced 4 more times

ld: error: undefined symbol: av_strdup
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced 29 more times

ld: error: undefined symbol: av_mallocz
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(graph_parse)
>>> referenced by ld-temp.o
>>>               lto.tmp:(graph_parse)
>>> referenced 62 more times

ld: error: undefined symbol: av_opt_set_defaults
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(avfilter_graph_alloc)
>>> referenced by ld-temp.o
>>>               lto.tmp:(avfilter_graph_alloc_filter)
>>> referenced 5 more times

ld: error: undefined symbol: av_fast_malloc
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)

ld: error: undefined symbol: av_free
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced 62 more times

ld: error: undefined symbol: av_freep
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced 205 more times

ld: error: undefined symbol: av_asprintf
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(ifile_open)
>>> referenced by ld-temp.o
>>>               lto.tmp:(describe_filter_link)
>>> referenced 3 more times

ld: error: too many errors emitted, stopping now (use -error-limit=0 to see all errors)
clang-14: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [Makefile:131: ffmpeg_g] Error 1


  


  I also compiled LAME encoder (version 3.100) with LTO options, and it worked just fine.
  
How to resolve the error ?

  


  **The libLTO.so file is present under lib64/ hence added that to the —extra-ldflags optional config.
  
**PATH env contains $HOME/Downloads/android-ndk-r25c/toolchains/llvm/prebuilt/linux-x86_64/bin