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• Should H.264 bit rate be multiples of 8 ?

  31 août 2016, par Dan Sharp

  I’m working on a video platform receiving H.264 video and building an HLS stream (transmuxing the H.264 to Mpeg2 TS segments via calls to ffmpeg).

  I wanted to set the bit rate to be about 2000 kbps, but I’m wondering : does it matter if it’s 2000 or 2048 ?

  In other words, do things calculate better if the bit rate is multiples of 8, like 512 or 2024 or 2048 ?

  I don’t know enough about how the bit rate is used, either on the sending side (camera) or on the processing side (ffmpeg).

  From tests... I can’t see any noticeable difference between 2000 and 2048, but maybe one is slightly better than another for the transmuxing and segmenting ?

  I welcome any thoughts/advice.

• How to find best FFmpeg libx265 encoding settings for a specific (set of) file(s)

  19 mai 2020, par Boba0514

  I have only recently discovered FFmpeg and tried using the x265 video codec to reduce the video stream size for some videos, and realized that I can achieve tremendous space savings, especially for video recorded via smarthphones. As I'm new to this, I tried doing some research and found that mostly it's about choosing the correct CRF and preset, so I am thinking it would be sufficient to write a script which iterates through these, creating samples which I could look at and decide what's the best option for a given (set of) video(s).

  



  Is this enough, or should I take some other things into consideration as well ? If so, what would the best solution ? What is the potential range for a good CRF value ? (I am thinking 20-30)

  


• How can I get FFmpeg to locate installed libraries when —sysroot is pointing to another directory ?

  3 février 2013, par Xaero Degreaz

  I've been going at this, literally for days. I'm trying to build FFmpeg with libmp3lame for use in an Android application. The build script sets a --sysroot flag that points to the Android NDK directory necessary to build these libraries in a way that Android can use them.

  The problem comes when I add the flag to --enable-libmp3lame ; I get ERROR: libmp3lame >= 3.98.3 not found during the build start up. I know that LAME, and it's libraries are installed, because I can just run ./configure --enable-libmp3lame manually and the configuration launches without a hitch, and shows that libmp3lame is enabled for this build. However, building like this will simply not work for what I need it for, since I need the Android NDK to do some work.

  I've tracked the problem down to the fact that this build script is declaring the sysroot, and through some research, I've tried adding -Luser/include, -L/user/includeto the extra cflags, and ldflags (which I've read is the default search location for gcc). I've tried several other things as well, but I'm confident that someone out here can help with this specific problem. This entire build script is as follows :

  Extra info :

  • Build OS : Ubuntu 11.10
  • FFmpeg Ver : Latest from git
  • LAME Ver : 3.9.x
  • Android NDK : r7

  build.sh

  #!/bin/bash
  
  
  
  if [ "$NDK" = "" ]; then
  
      echo NDK variable not set, assuming ${HOME}/android-ndk
  
      export NDK=${HOME}/android-ndk
  
  fi
  
  
  
  SYSROOT=$NDK/platforms/android-3/arch-arm
  
  # Expand the prebuilt/* path into the correct one
  
  TOOLCHAIN=`echo $NDK/toolchains/arm-linux-androideabi-4.4.3/prebuilt/*-x86`
  
  export PATH=$TOOLCHAIN/bin:$PATH
  
  
  
  rm -rf build/ffmpeg
  
  mkdir -p build/ffmpeg
  
  cd ffmpeg
  
  
  
  # Don't build any neon version for now
  
  for version in armv5te armv7a; do
  
  
  
          DEST=../build/ffmpeg
  
          FLAGS="--target-os=linux --cross-prefix=arm-linux-androideabi- --arch=arm"
  
          FLAGS="$FLAGS --sysroot=$SYSROOT"
  
          FLAGS="$FLAGS --soname-prefix=/data/data/net.smartnotes/lib/"
  
          FLAGS="$FLAGS --enable-shared --disable-symver"
  
          FLAGS="$FLAGS --enable-small --optimization-flags=-O2"
  
          FLAGS="$FLAGS --disable-everything --enable-protocol=file"
  
          FLAGS="$FLAGS --enable-libmp3lame --enable-encoder=nellymoser"
  
  
  
          case "$version" in
  
                  neon)
  
                      EXTRA_CFLAGS="-march=armv7-a -mfloat-abi=softfp -mfpu=neon"
  
                      EXTRA_LDFLAGS="-Wl,--fix-cortex-a8"
  
                      # Runtime choosing neon vs non-neon requires
  
                      # renamed files
  
                      ABI="armeabi-v7a"
  
                      ;;
  
                  armv7a)
  
                      # I have tried many things here.
  
                      EXTRA_CFLAGS="-march=armv7-a -mfloat-abi=softfp"
  
                      EXTRA_LDFLAGS=""
  
                      ABI="armeabi-v7a"
  
                      ;;
  
                  *)
  
                      # I have tried many things here.
  
                      EXTRA_CFLAGS="-Luser/include"
  
                      EXTRA_LDFLAGS=""
  
                      ABI="armeabi"
  
                      ;;
  
          esac
  
          DEST="$DEST/$ABI"
  
          FLAGS="$FLAGS --prefix=$DEST"
  
  
  
          mkdir -p $DEST
  
          echo $FLAGS --extra-cflags="$EXTRA_CFLAGS" --extra-ldflags="$EXTRA_LDFLAGS" > $DEST/info.txt
  
          ./configure $FLAGS --extra-cflags="$EXTRA_CFLAGS" --extra-ldflags="$EXTRA_LDFLAGS" | tee $DEST/configuration.txt
  
          [ $PIPESTATUS == 0 ] || exit 1
  
          make clean
  
          make -j4 || exit 1
  
          make install || exit 1
  
  
  
  done