Encoding RGB frames using x264 and AVCodec in C

Question

I have RGB24 frames streamed from camera and i want to encode them into h264 ,i found that AVCodec and x264 can do so, the problem is x264 as default accepts YUV420 as input so what i wrote was a program which convert RGB frames to YUV420 .that was by sws_scale function .this works well except that it does not satisfy the required FPS because the converting (RGB->YUV420) takes time.

This is how i setup my encoder context :

videoStream->id = 0;
vCodecCtx = videoStream->codec;

vCodecCtx->coder_type       = AVMEDIA_TYPE_VIDEO;
vCodecCtx->codec_id         = AV_CODEC_ID_H264;
vCodecCtx->bit_rate         = 400000;
vCodecCtx->width            = Width;
vCodecCtx->height           = Height;
vCodecCtx->time_base.den    = FPS;
vCodecCtx->time_base.num    = 1;
//vCodecCtx->time_base      = (AVRational){1,};
vCodecCtx->gop_size         = 12;
vCodecCtx->max_b_frames     = 1;
vCodecCtx->pix_fmt          = AV_PIX_FMT_YUV420P;

if(formatCtx->oformat->flags & AVFMT_GLOBALHEADER)
    vCodecCtx->flags |= CODEC_FLAG_GLOBAL_HEADER;

av_opt_set(vCodecCtx->priv_data, "preset", "ultrafast", 0);
av_opt_set(vCodecCtx->priv_data, "profile", "baseline", AV_OPT_SEARCH_CHILDREN);

if (avcodec_open2(vCodecCtx, h264Codec, NULL) < 0){
    return 0;
}

when i changes AV_PIX_FMT_YUV420P to AV_PIX_FMT_RGB24 ,avcodec_open2 will fail. i read that there is a version of libx264 for RGB called libx264rgb but i even dont know whether i have to rebuild x264 with enabling this option or to download another source or i have to do it programmatically with the first x264 lib.

the question is how to enable RGB as input to libx264 to use with libavcodec in C .or how to make the encoding or sws_scale more fast .

Edit:

How i built ffmpeg :

NDK=D:/AndroidDev/android-ndk-r9
PLATFORM=$NDK/platforms/android-18/arch-arm/
PREBUILT=$NDK/toolchains/arm-linux-androideabi-4.8/prebuilt/windows-x86_64

GENERAL="\
--enable-small \
--enable-cross-compile \
--extra-libs="-lgcc" \
--arch=arm \
--cc=$PREBUILT/bin/arm-linux-androideabi-gcc \
--cross-prefix=$PREBUILT/bin/arm-linux-androideabi- \
--nm=$PREBUILT/bin/arm-linux-androideabi-nm \
--extra-cflags="-I../x264/android/arm/include" \
--extra-ldflags="-L../x264/android/arm/lib" "


MODULES="\
--enable-gpl \
--enable-libx264"

function build_ARMv6
{
  ./configure \
  --target-os=linux \
  --prefix=./android/armeabi \
  ${GENERAL} \
  --sysroot=$PLATFORM \
  --enable-shared \
  --disable-static \
  --extra-cflags=" -O3 -fpic -fasm -Wno-psabi -fno-short-enums -fno-strict-aliasing -finline-limit=300 -mfloat-abi=softfp -mfpu=vfp -marm -march=armv6" \
  --extra-ldflags="-lx264 -Wl,-rpath-link=$PLATFORM/usr/lib -L$PLATFORM/usr/lib -nostdlib -lc -lm -ldl -llog" \
  --enable-zlib \
  ${MODULES} \
  --disable-doc \
  --enable-neon

  make clean
  make
  make install
}

build_ARMv6

echo Android ARMEABI builds finished

How i built x264 :

NDK=D:/AndroidDev/android-ndk-r9
PLATFORM=$NDK/platforms/android-18/arch-arm/
TOOLCHAIN=$NDK/toolchains/arm-linux-androideabi-4.8/prebuilt/windows-x86_64
PREFIX=./android/arm

function build_one
{
  ./configure \
  --prefix=$PREFIX \
  --enable-static \
  --enable-pic \
  --host=arm-linux \
  --cross-prefix=$TOOLCHAIN/bin/arm-linux-androideabi- \
  --sysroot=$PLATFORM

  make clean
  make
  make install
}

build_one

echo Android ARM builds finished

Answer 1

To use RGB pixel formats (AV_PIX_FMT_BGR0, AV_PIX_FMT_BGR24, AV_PIX_FMT_RGB24) with libx264 in libavcodec you need:

1. use libavcodec from ffmpeg project and not from libav project because currently it is only available in there;
2. make sure that libavcodec was compiled with libx264rgb (CONFIG_LIBX264RGB_ENCODER) which as I understand would be enabled if you would use new enough 8-bit libx264 (configured with --enable-libx264);
3. use avcodec_find_encoder_by_name("libx264rgb") instead of avcodec_find_encoder(AV_CODEC_ID_H264).