我目前正在开展一个FFMPEG项目。我正在尝试使用此代码将RGB图像转换为YUV图像（我昨晚在互联网上找到了它）：
void Decode::video_encode_example(const char *filename, int codec_id)
{
AVCodec *codec;
AVCodecContext *c= NULL;
int i, ret, x, y, got_output;
FILE *f;
AVFrame *frame;
AVPacket pkt;
uint8_t endcode[] = { 0, 0, 1, 0xb7 };
printf("Encode video file %s\n", filename);
/* find the mpeg1 video encoder */
codec = avcodec_find_encoder((enum AVCodecID)codec_id);
if (!codec) {
fprintf(stderr, "Codec not found\n");
exit(1);
}
c = avcodec_alloc_context3(codec);
if (!c) {
fprintf(stderr, "Could not allocate video codec context\n");
exit(2);
}
/* put sample parameters */
c->bit_rate = 400000;
/* resolution must be a multiple of two */
c->width = 352;
c->height = 288;
/* frames per second */
c->time_base = (AVRational){1,25};
/* emit one intra frame every ten frames
* check frame pict_type before passing frame
* to encoder, if frame->pict_type is AV_PICTURE_TYPE_I
* then gop_size is ignored and the output of encoder
* will always be I frame irrespective to gop_size
*/
c->gop_size = 10;
c->max_b_frames = 1;
c->pix_fmt = AV_PIX_FMT_YUV420P;
if (codec_id == AV_CODEC_ID_H264)
av_opt_set(c->priv_data, "preset", "slow", 0);
/* open it */
if (avcodec_open2(c, codec, NULL) < 0) {
fprintf(stderr, "Could not open codec\n");
exit(3);
}
f = fopen(filename, "wb");
if (!f) {
fprintf(stderr, "Could not open %s\n", filename);
exit(4);
}
frame = avcodec_alloc_frame();// Dans une version plus récente c'est av_frame_alloc
if (!frame) {
fprintf(stderr, "Could not allocate video frame\n");
exit(5);
}
frame->format = c->pix_fmt;
frame->width = c->width;
frame->height = c->height;
/* the image can be allocated by any means and av_image_alloc() is
* just the most convenient way if av_malloc() is to be used */
ret = av_image_alloc(frame->data, frame->linesize, c->width, c->height,
c->pix_fmt, 32);
if (ret < 0) {
fprintf(stderr, "Could not allocate raw picture buffer\n");
exit(6);
}
//
// RGB to YUV:
// http://stackoverflow.com/questions/16667687/how-to-convert-rgb-from-yuv420p-for-ffmpeg-encoder
//
// Create some dummy RGB "frame"
uint8_t *rgba32Data = new uint8_t[4*c->width*c->height];
SwsContext * ctx = sws_getContext(c->width, c->height,
AV_PIX_FMT_RGBA, c->width, c->height,
AV_PIX_FMT_YUV420P, 0, 0, 0, 0);
/* encode 1 second of video */
for (i = 0; i < 25; i++) {
av_init_packet(&pkt);
pkt.data = NULL; // packet data will be allocated by the encoder
pkt.size = 0;
fflush(stdout);
/* prepare a dummy image */
/* Y */
// for (y = 0; y < c->height; y++) {
// for (x = 0; x < c->width; x++) {
// frame->data[0][y * frame->linesize[0] + x] = x + y + i * 3;
// }
// }
//
// /* Cb and Cr */
// for (y = 0; y < c->height/2; y++) {
// for (x = 0; x < c->width/2; x++) {
// frame->data[1][y * frame->linesize[1] + x] = 128 + y + i * 2;
// frame->data[2][y * frame->linesize[2] + x] = 64 + x + i * 5;
// }
// }
uint8_t *pos = rgba32Data;
for (y = 0; y < c->height; y++)
{
for (x = 0; x < c->width; x++)
{
pos[0] = i / (float)25 * 255;
pos[1] = 0;
pos[2] = x / (float)(c->width) * 255;
pos[3] = 255;
pos += 4;
}
}
uint8_t * inData[1] = { rgba32Data }; // RGBA32 have one plane
//
// NOTE: In a more general setting, the rows of your input image may
// be padded; that is, the bytes per row may not be 4 * width.
// In such cases, inLineSize should be set to that padded width.
//
int inLinesize[1] = { 4*c->width }; // RGBA stride
sws_scale(ctx, inData, inLinesize, 0, c->height, frame->data, frame->linesize);
frame->pts = i;
/* encode the image */
ret = avcodec_encode_video2(c, &pkt, frame, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding frame\n");
exit(7);
}
if (got_output) {
printf("Write frame %3d (size=%5d)\n", i, pkt.size);
fwrite(pkt.data, 1, pkt.size, f);
av_free_packet(&pkt);
}
}
/* get the delayed frames */
for (got_output = 1; got_output; i++) {
fflush(stdout);
ret = avcodec_encode_video2(c, &pkt, NULL, &got_output);
if (ret < 0) {
fprintf(stderr, "Error encoding frame\n");
exit(8);
}
if (got_output) {
printf("Write frame %3d (size=%5d)\n", i, pkt.size);
fwrite(pkt.data, 1, pkt.size, f);
av_free_packet(&pkt);
}
}
/* add sequence end code to have a real mpeg file */
fwrite(endcode, 1, sizeof(endcode), f);
fclose(f);
avcodec_close(c);
av_free(c);
av_freep(&frame->data[0]);
avcodec_free_frame(&frame);// Dans une version plus récente c'est av_frame_alloc
printf("\n");
}
int main()
{
Decode d;
avcodec_register_all();
d.video_encode_example("/home/Dave/Desktop/test.mpg",AV_CODEC_ID_MPEG2VIDEO);
}
当我运行此应用程序时，我的Linux终端显示以下错误：
[swscaler @ 0x1e1dc60]必须选择一个缩放器算法 分段错误（核心转储）
我不知道实际发生了什么。你能帮帮我吗？
答案 0 :(得分：1)
SwsContext * ctx = sws_getContext(c->width, c->height, AV_PIX_FMT_RGBA, c->width, c->height, AV_PIX_FMT_YUV420P, 0, 0, 0, 0);
你的＆＃34;旗帜＆＃34;字段（请参阅https://gcc.gnu.org/onlinedocs/cpp/Character-sets.html - 4个零列表中的第一个）需要非零。有效值为docs顶部列表中的SWS_FAST_BILINEAR - SWS_ERROR_DIFFUSION。一个好的默认设置是仅设置缩放算法，并使用例如this page作为SWS_BICUBIC插值的值。高端缩放算法（如bicubic插值的SPS_SPLINE）将更加计算密集，而低端缩放算法（如spline插值的SWS_POINT）倾向于看起来更糟糕的是，您在此选择的确切值取决于您愿意花多少CPU以及您对最终结果的视觉质量的关注程度。