这是我的第一个问题，所以我希望我做得正确。如果没有，请让我知道解决它。
我试图使用ffmpeg库将短暂的（10秒）mp4视频文件转换为gif（我很高兴使用ffmpeg）。该程序很好地转换为gif，但有时会随机崩溃。
这是我使用的ffmpeg库的版本：
libavutil 54. 27.100
libavcodec 56. 41.100
libavformat 56. 36.100
libavdevice 56. 4.100
libavfilter 5. 16.101
libavresample 2. 1. 0
libswscale 3. 1.101
libswresample 1. 2.100
libpostproc 53. 3.100
我使用的是1920x1080p的视频，所以为了生成gif我正在进行像素格式转换，从AV_PIX_FMT_YUV420P到AV_PIX_FMT_RGB8，从初始分辨率调整大小至432x240p。
以下是代码：
int VideoManager::loadVideo(QString filename, bool showInfo)
{
if(avformat_open_input(&iFmtCtx, filename.toStdString().c_str(), 0, 0) < 0)
{
qDebug() << "Could not open input file " << filename;
closeInput();
return -1;
}
if (avformat_find_stream_info(iFmtCtx, 0) < 0)
{
qDebug() << "Failed to retrieve input stream information";
closeInput();
return -2;
}
videoStreamIndex = -1;
for(unsigned int i = 0; i < iFmtCtx->nb_streams; ++i)
if(iFmtCtx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO)
{
videoStreamIndex = i;
break;
}
if(videoStreamIndex == -1)
{
qDebug() << "Didn't find any video stream!";
closeInput();
return -3;
}
iCodecCtx = iFmtCtx->streams[videoStreamIndex]->codec;
iCodec = avcodec_find_decoder(iCodecCtx->codec_id);
if(iCodec == NULL) // Codec not found
{
qDebug() << "Codec not found!";
closeInput();
return -4;
}
if(avcodec_open2(iCodecCtx, iCodec, NULL) < 0)
{
qDebug() << "Could not open codec!";
closeInput();
return -1;
}
if(showInfo)
av_dump_format(iFmtCtx, 0, filename.toStdString().c_str(), 0);
return 0;
}
void VideoManager::generateGif(QString filename)
{
int ret, frameCount = 0;
AVPacket packet;
packet.data = NULL;
packet.size = 0;
AVFrame *frame = NULL;
unsigned int stream_index;
int got_frame;
gifHeight = iFmtCtx->streams[videoStreamIndex]->codec->height;
gifWidth = iFmtCtx->streams[videoStreamIndex]->codec->width;
if(gifHeight > MAX_GIF_HEIGHT || gifWidth > MAX_GIF_WIDTH)
{
if(gifHeight > gifWidth)
{
gifWidth = (float)gifWidth * ( (float)MAX_GIF_HEIGHT / (float)gifHeight );
gifHeight = MAX_GIF_HEIGHT;
}
else
{
gifHeight = (float)gifHeight * ( (float)MAX_GIF_WIDTH / (float)gifWidth );
gifWidth = MAX_GIF_WIDTH;
}
}
if(openOutputFile(filename.toStdString().c_str()) < 0)
{
qDebug() << "Error openning output file: " << filename;
return;
}
while (1) {
int ret = av_read_frame(iFmtCtx, &packet);
if (ret < 0)
{
if(ret != AVERROR_EOF)
qDebug() << "Error reading frame: " << ret;
break;
}
stream_index = packet.stream_index;
if(stream_index == videoStreamIndex)
{
frame = av_frame_alloc();
if (!frame) {
qDebug() << "Error allocating frame";
break;
}
av_packet_rescale_ts(&packet,
iFmtCtx->streams[stream_index]->time_base,
iFmtCtx->streams[stream_index]->codec->time_base);
ret = avcodec_decode_video2(iFmtCtx->streams[stream_index]->codec, frame,
&got_frame, &packet);
if (ret < 0) {
qDebug() << "Decoding failed";
break;
}
if(got_frame)
{
qDebug() << ++frameCount;
nframes++;
frame->pts = av_frame_get_best_effort_timestamp(frame);
////////////////////////////////////////////////////////////////////////////////
/// Pixel format convertion and resize
////////////////////////////////////////////////////////////////////////////////
uint8_t *out_buffer = NULL;
SwsContext *img_convert_ctx = NULL;
AVFrame *pFrameRGB = av_frame_alloc();
if(pFrameRGB == NULL)
{
qDebug() << "Error allocating frameRGB";
break;
}
AVPixelFormat pixFmt;
switch (iFmtCtx->streams[stream_index]->codec->pix_fmt)
{
case AV_PIX_FMT_YUVJ420P : pixFmt = AV_PIX_FMT_YUV420P; break;
case AV_PIX_FMT_YUVJ422P : pixFmt = AV_PIX_FMT_YUV422P; break;
case AV_PIX_FMT_YUVJ444P : pixFmt = AV_PIX_FMT_YUV444P; break;
case AV_PIX_FMT_YUVJ440P : pixFmt = AV_PIX_FMT_YUV440P; break;
default:
pixFmt = iFmtCtx->streams[stream_index]->codec->pix_fmt;
}
out_buffer = (uint8_t*)av_malloc( avpicture_get_size( AV_PIX_FMT_RGB8,
gifWidth,
gifHeight ));
if(!out_buffer)
{
qDebug() << "Error alocatting out_buffer!";
}
avpicture_fill((AVPicture *)pFrameRGB, out_buffer, AV_PIX_FMT_RGB8,
gifWidth,
gifHeight);
img_convert_ctx = sws_getContext( iFmtCtx->streams[stream_index]->codec->width,
iFmtCtx->streams[stream_index]->codec->height,
pixFmt,
gifWidth,
gifHeight,
AV_PIX_FMT_RGB8,
SWS_ERROR_DIFFUSION, NULL, NULL, NULL );
if(!img_convert_ctx)
{
qDebug() << "error getting sws context";
}
sws_scale( img_convert_ctx, (const uint8_t* const*)frame->data,
frame->linesize, 0,
iFmtCtx->streams[stream_index]->codec->height,
pFrameRGB->data,
pFrameRGB->linesize );
pFrameRGB->format = AV_PIX_FMT_RGB8;
pFrameRGB->pts = frame->pts;
pFrameRGB->best_effort_timestamp = frame->best_effort_timestamp;
pFrameRGB->width = gifWidth;
pFrameRGB->height = gifHeight;
pFrameRGB->pkt_dts = frame->pkt_dts;
pFrameRGB->pkt_pts = frame->pkt_pts;
pFrameRGB->pkt_duration = frame->pkt_duration;
pFrameRGB->pkt_pos = frame->pkt_pos;
pFrameRGB->pkt_size = frame->pkt_size;
pFrameRGB->interlaced_frame = frame->interlaced_frame;
////////////////////////////////////////////////////////////////////////////////
ret = encodeAndWriteFrame(pFrameRGB, stream_index, NULL);
//av_frame_free(&frame);
//av_free(out_buffer);
//sws_freeContext(img_convert_ctx);
if (ret < 0)
{
qDebug() << "Error encoding and writting frame";
//av_free_packet(&packet);
closeOutput();
}
}
else {
//av_frame_free(&frame);
}
}
av_free_packet(&packet);
}
ret = flushEncoder(videoStreamIndex);
if (ret < 0)
{
qDebug() << "Flushing encoder failed";
}
av_write_trailer(oFmtCtx);
//av_free_packet(&packet);
//av_frame_free(&frame);
closeOutput();
}
void VideoManager::closeOutput()
{
if (oFmtCtx && oFmtCtx->nb_streams > 0 && oFmtCtx->streams[0] && oFmtCtx->streams[0]->codec)
avcodec_close(oFmtCtx->streams[0]->codec);
if (oFmtCtx && oFmt && !(oFmt->flags & AVFMT_NOFILE))
avio_closep(&oFmtCtx->pb);
avformat_free_context(oFmtCtx);
}
int VideoManager::openOutputFile(const char *filename)
{
AVStream *out_stream;
AVStream *in_stream;
AVCodecContext *dec_ctx, *enc_ctx;
AVCodec *encoder;
int ret;
oFmtCtx = NULL;
avformat_alloc_output_context2(&oFmtCtx, NULL, NULL, filename);
if (!oFmtCtx) {
qDebug() << "Could not create output context";
return AVERROR_UNKNOWN;
}
oFmt = oFmtCtx->oformat;
out_stream = avformat_new_stream(oFmtCtx, NULL);
if (!out_stream) {
qDebug() << "Failed allocating output stream";
return AVERROR_UNKNOWN;
}
in_stream = iFmtCtx->streams[videoStreamIndex];
dec_ctx = in_stream->codec;
enc_ctx = out_stream->codec;
encoder = avcodec_find_encoder(AV_CODEC_ID_GIF);
if (!encoder) {
qDebug() << "FATAL!: Necessary encoder not found";
return AVERROR_INVALIDDATA;
}
enc_ctx->height = gifHeight;
enc_ctx->width = gifWidth;
enc_ctx->sample_aspect_ratio = dec_ctx->sample_aspect_ratio;
enc_ctx->pix_fmt = AV_PIX_FMT_RGB8;
enc_ctx->time_base = dec_ctx->time_base;
ret = avcodec_open2(enc_ctx, encoder, NULL);
if (ret < 0) {
qDebug() << "Cannot open video encoder for gif";
return ret;
}
if (oFmt->flags & AVFMT_GLOBALHEADER)
enc_ctx->flags |= CODEC_FLAG_GLOBAL_HEADER;
if (!(oFmt->flags & AVFMT_NOFILE)) {
ret = avio_open(&oFmtCtx->pb, filename, AVIO_FLAG_WRITE);
if (ret < 0) {
qDebug() << "Could not open output file " << filename;
return ret;
}
}
ret = avformat_write_header(oFmtCtx, NULL);
if (ret < 0) {
qDebug() << "Error occurred when opening output file";
return ret;
}
return 0;
}
int VideoManager::encodeAndWriteFrame(AVFrame *frame, unsigned int stream_index, int *got_frame) {
int ret;
int got_frame_local;
AVPacket enc_pkt;
if (!got_frame)
got_frame = &got_frame_local;
enc_pkt.data = NULL;
enc_pkt.size = 0;
av_init_packet(&enc_pkt);
ret = avcodec_encode_video2(oFmtCtx->streams[stream_index]->codec, &enc_pkt,
frame, got_frame);
//av_frame_free(&frame);
if (ret < 0)
return ret;
if (!(*got_frame))
return 0;
enc_pkt.stream_index = stream_index;
av_packet_rescale_ts(&enc_pkt,
oFmtCtx->streams[stream_index]->codec->time_base,
oFmtCtx->streams[stream_index]->time_base);
ret = av_interleaved_write_frame(oFmtCtx, &enc_pkt);
return ret;
}
int VideoManager::flushEncoder(unsigned int stream_index)
{
int ret;
int got_frame;
if (!(oFmtCtx->streams[stream_index]->codec->codec->capabilities &
CODEC_CAP_DELAY))
return 0;
while (1) {
ret = encodeAndWriteFrame(NULL, stream_index, &got_frame);
if (ret < 0)
break;
if (!got_frame)
return 0;
}
return ret;
}
我知道有很多内存泄漏。我删除/评论了大部分免费功能的意图，因为我认为这是问题所在。
我使用Qtcreator，所以当我调试程序时，这是输出：
Level Function Line
0 av_image_copy 303
1 frame_copy_video 650
2 av_frame_copy 687
3 av_frame_ref 384
4 gif_encode_frame 307
5 avcodec_encode_video2 2191
6 VideoManager::encodeAndWriteFrame 813
7 VideoManager::generateGif 375
8 qMain 31
9 WinMain*16 112
10 main
我已检查过程序崩溃是否存在特定帧，但它也是一个随机帧。
知道我做错了什么？任何帮助都将非常感激。
修改
经过几天的痛苦，痛苦和挫折之后，我决定从头开始编写整个代码。两次我都是从this示例开始并修改它以便像我之前描述的那样工作。它现在完美地运作：D！我在旧代码（之前发布）中找到的唯一错误是当我尝试访问我使用videoStreamIndex的输出文件中的视频流时，但该索引来自输入文件中的视频流。有时它可能是相同的索引，有时则不是。但它并没有解释为什么它会随机崩溃。如果这是崩溃的原因，每次我使用相同的视频运行代码时它都应该崩溃。可能，该代码中存在更多错误。
请注意，如果在上面的代码中修复该错误实际上解决了崩溃问题，我还没有测试过。
答案 0 :(得分：0)
我认为你的参数可能会混淆。 According to what I'm reading from the documentation avcodec_decode_video2的原型如下：
int avcodec_decode_video2 (AVCodecContext * avctx,
AVFrame * picture,
int * got_picture_ptr,
const AVPacket * avpkt)
并且被称为：
ret = avcodec_encode_video2(oFmtCtx->streams[stream_index]->codec, // Dunno.
&enc_pkt, //AVPacket * should be AVFrame *
frame, //AVFrame * Should be int *
got_frame); // int * should be AVPacket *