はじめに
これまでは映像データを取り扱うときにOpenCVのVideoCaptureやVideoWriterを使っていたのですが、FFmpegのAPIを使ったほうがいろいろと融通が利くかなと思ったので、今回はそのコードを書いてみました。
(googleで検索をかけると avcodec_decode_video2() や avpicture_fill() などを使ったコードが見つかるのですが、これらの関数は現在deprecatedとなっているので、今のAPIに即したものを書いてみました。)
コード
ということで、映像ファイル(ここではmp4)を読みこみ、そのネガポジ反転をした映像を書き込むための試験的なコードがこちら。デコードした生のデータ処理自体はOpenCVで行うのがいいかもしれません。
(2021/09/14 追記：タイムスタンプ関連の箇所を変更しました)
(2021/09/17 追記：メモリ解放関連の箇所を修正しました)
#include <iostream>
extern "C"{
#include <libavformat/avformat.h>
#include <libavcodec/avcodec.h>
#include <libavutil/imgutils.h>
#include <libavutil/opt.h>
#include <libswscale/swscale.h>
#include <libswresample/swresample.h>
}
void decode_and_encode_video(const char *output, const char *input);
int main(int argc, char *argv[]){
const char *input = argv[1];
const char *output = argv[2];
decode_and_encode_video(output, input);
return 0;
}
void decode_and_encode_video(const char *output, const char *input){
AVFormatContext *inputFmtContxt = NULL;
AVFormatContext *outputFmtContxt = NULL;
const AVCodec *encoder = NULL;
const AVCodec *decoder = NULL;
AVCodecContext *encoderContxt = NULL;
AVCodecContext *decoderContxt = NULL;
int ret = 0, video_stream_index = 0;
ret = avformat_open_input(&inputFmtContxt, input, NULL, NULL);
if (ret < 0){
std::cout << "Could not open input video" << std::endl;
}
ret = avformat_find_stream_info(inputFmtContxt, NULL);
if (ret < 0){
std::cout << "Could not find the stream info" << std::endl;
}
const AVOutputFormat *outFmt = av_guess_format("mp4", NULL, NULL);
avformat_alloc_output_context2(&outputFmtContxt, outFmt, NULL, NULL);
//デコーダーとエンコーダーを設定
for (int i=0; i<(int)inputFmtContxt->nb_streams; ++i){
AVStream *in_stream = inputFmtContxt->streams[i];
AVCodecParameters *in_par = in_stream->codecpar;
AVStream *out_stream = avformat_new_stream(outputFmtContxt, NULL);
if (in_par->codec_type == AVMEDIA_TYPE_VIDEO){
video_stream_index = i;
decoder = avcodec_find_decoder(in_par->codec_id);
decoderContxt = avcodec_alloc_context3(decoder);
avcodec_parameters_to_context(decoderContxt, in_par);
decoderContxt->framerate = in_stream->r_frame_rate;
decoderContxt->time_base = in_stream->time_base;
avcodec_open2(decoderContxt, decoder, NULL);
encoder = avcodec_find_encoder(in_par->codec_id);
encoderContxt = avcodec_alloc_context3(encoder);
encoderContxt->height = decoderContxt->height;
encoderContxt->width = decoderContxt->width;
encoderContxt->pix_fmt = decoderContxt->pix_fmt;
encoderContxt->qmax = 31;
encoderContxt->qmin = 2;
encoderContxt->qcompress = 0.6;
encoderContxt->max_qdiff = 4;
encoderContxt->gop_size = 250;
encoderContxt->keyint_min = 25;
encoderContxt->max_b_frames = 16;
encoderContxt->refs = 6;
encoderContxt->framerate = in_stream->r_frame_rate;
encoderContxt->time_base = in_stream->time_base;
encoderContxt->bit_rate = decoderContxt->bit_rate;
encoderContxt->flags = AV_CODEC_FLAG_GLOBAL_HEADER;
av_opt_set(encoderContxt->priv_data, "preset", "fast", 0);
av_opt_set(encoderContxt->priv_data, "tune", "zerolatency", 0);
avcodec_open2(encoderContxt, encoder, NULL);
out_stream->time_base = encoderContxt->time_base;
avcodec_parameters_from_context(out_stream->codecpar, encoderContxt);
}
else{
ret = avcodec_parameters_copy(out_stream->codecpar, in_par);
}
}
//出力ファイルを準備
av_dump_format(outputFmtContxt, 0, output, 1);
avio_open(&outputFmtContxt->pb, output, AVIO_FLAG_WRITE);
ret = avformat_write_header(outputFmtContxt, NULL);
//YUV と RGB 間の変換用
enum AVPixelFormat bgr_pix_fmt = AV_PIX_FMT_BGR24;
int HEIGHT = decoderContxt->height;
int WIDTH = decoderContxt->width;
SwsContext *yuv2bgr = sws_getContext(WIDTH, HEIGHT, decoderContxt->pix_fmt,
WIDTH, HEIGHT, bgr_pix_fmt, SWS_BICUBIC, NULL, NULL, NULL);
SwsContext *bgr2yuv = sws_getContext(WIDTH, HEIGHT, bgr_pix_fmt,
WIDTH, HEIGHT, encoderContxt->pix_fmt, SWS_BICUBIC, NULL, NULL, NULL);
//パケットとフレームの準備
int res = 0;
AVPacket *packet = av_packet_alloc();
AVPacket *out_packet = av_packet_alloc();
out_packet->data = NULL;
out_packet->size = 0;
// デコーダーから受け取るフレーム
AVFrame *frame = av_frame_alloc();
// RGBへの変換先のフレーム
AVFrame *bgrframe = av_frame_alloc();
bgrframe->width = decoderContxt->width;
bgrframe->height = decoderContxt->height;
bgrframe->format = bgr_pix_fmt;
ret = av_frame_get_buffer(bgrframe, 0);
uint8_t *buf = (uint8_t*) av_malloc(av_image_get_buffer_size(AV_PIX_FMT_BGR24, decoderContxt->width, decoderContxt->height, 1));
ret = av_image_fill_arrays(bgrframe->data, bgrframe->linesize, buf, AV_PIX_FMT_BGR24, decoderContxt->width, decoderContxt->height, 1);
// エンコーダ―に渡すフレーム
AVFrame *outframe = av_frame_alloc();
outframe->width = decoderContxt->width;
outframe->height = decoderContxt->height;
outframe->format = decoderContxt->pix_fmt;
ret = av_frame_get_buffer(outframe, 0);
uint8_t *outbuf = (uint8_t*) av_malloc(av_image_get_buffer_size(AV_PIX_FMT_YUV420P, decoderContxt->width, decoderContxt->height, 1));
ret = av_image_fill_arrays(outframe->data, outframe->linesize, outbuf, AV_PIX_FMT_YUV420P, decoderContxt->width, decoderContxt->height, 1);
//デコードとエンコードを開始
while (true){
ret = av_read_frame(inputFmtContxt, packet);
if (ret < 0){
break;
}
AVStream *input_stream = inputFmtContxt->streams[packet->stream_index];
AVStream *output_stream = outputFmtContxt->streams[packet->stream_index];
if (input_stream->codecpar->codec_type == video_stream_index){
res = avcodec_send_packet(decoderContxt, packet);
while (res >= 0){
res = avcodec_receive_frame(decoderContxt, frame);
if (res == AVERROR(EAGAIN) || res == AVERROR_EOF){
break;
}
if (res >= 0){
outframe->pict_type = frame->pict_type;
outframe->pts = frame->pts;
outframe->pkt_dts = frame->pkt_dts;
outframe->pkt_duration = frame->pkt_duration;
ret = av_frame_make_writable(outframe);
//YUVフレームをRGBフレームに変換
sws_scale(yuv2bgr, frame->data, frame->linesize, 0, frame->height, bgrframe->data, bgrframe->linesize);
//ネガポジ反転
int h = bgrframe->height;
int l = bgrframe->linesize[0];
for (int i=0; i<h; ++i){
for (int j=0; j<l; ++j){
bgrframe->data[0][i * l + j] = 255 - bgrframe->data[0][i * l + j];
}
}
//RGBからYUVに戻す
sws_scale(bgr2yuv, bgrframe->data, bgrframe->linesize, 0, h, outframe->data, outframe->linesize);
res = avcodec_send_frame(encoderContxt, outframe);
//フレームの書き込み
while (res >= 0){
res = avcodec_receive_packet(encoderContxt, out_packet);
if (res == AVERROR(EAGAIN) || res == AVERROR_EOF){
break;
}
out_packet->pts = av_rescale_q_rnd(outframe->pts, input_stream->time_base, output_stream->time_base, AV_ROUND_NEAR_INF);
out_packet->dts = outframe->pts;
out_packet->duration = av_rescale_q(packet->duration, input_stream->time_base, output_stream->time_base);
res = av_interleaved_write_frame(outputFmtContxt, out_packet);
}
av_packet_unref(out_packet);
}
av_frame_unref(frame);
}
av_packet_unref(packet);
}
else{
//音声データはそのまま書き込み
packet->pts = av_rescale_q_rnd(packet->pts, input_stream->time_base, output_stream->time_base, AV_ROUND_NEAR_INF);
packet->dts = av_rescale_q_rnd(packet->dts, input_stream->time_base, output_stream->time_base, AV_ROUND_NEAR_INF);
packet->duration = av_rescale_q(packet->duration, input_stream->time_base, output_stream->time_base);
res = av_interleaved_write_frame(outputFmtContxt, packet);
av_packet_unref(packet);
}
}
//各メモリの解放
av_packet_free(&packet);
av_frame_free(&frame);
avformat_free_context(inputFmtContxt);
avcodec_free_context(&decoderContxt);
av_packet_free(&out_packet);
av_write_trailer(outputFmtContxt);
avformat_free_context(outputFmtContxt);
avcodec_free_context(&encoderContxt);
av_freep(&buf);
av_freep(&outbuf);
sws_freeContext(yuv2bgr);
sws_freeContext(bgr2yuv);
}