下面的代码是一个类，用于通过add_frame()方法将多张图像转换为带有encode()的GIF。它还使用过滤器来生成和应用调色板。用法是这样的：
代码调用示例
std::unique_ptr<px::GIF::FFMPEG> gif_obj = nullptr;
try
{
gif_obj = std::make_unique<px::GIF::FFMPEG>({1000,1000}, 12, "C:/out.gif",
"format=pix_fmts=rgb24,split [a][b];[a]palettegen[p];[b][p]paletteuse");
// Example: a simple vector of images (usually process internally)
for(auto img : image_vector)
gif_obj->add_frame(img);
// Once all frame were added, encode the final GIF with the filter applied.
gif_obj->encode();
}
catch(const std::exception& e)
{
// An error occured! We must close FFMPEG properly and delete the created file.
gif_obj->cancel();
}
我有以下问题。如果代码由于任何原因引发异常，我将调用ffmpeg->cancel()，它假定要删除磁盘上的GIF文件。但这永远都行不通，我认为文件上有一个锁或类似的东西。所以这是我的问题：
关闭/释放ffmpeg对象以便随后删除文件的正确方法是什么？
下面的完整课程代码
标题
// C++ Standard includes
#include <memory>
#include <string>
#include <vector>
// 3rd Party incldues
#ifdef __cplusplus
extern "C" {
#include "libavformat/avformat.h"
#include "libavfilter/avfilter.h"
#include "libavutil/opt.h"
#include "libavfilter/buffersrc.h"
#include "libavfilter/buffersink.h"
#include "libswscale/swscale.h"
#include "libavutil/imgutils.h"
}
#endif
#define FFMPEG_MSG_LEN 2000
namespace px
{
namespace GIF
{
class FFMPEG
{
public:
FFMPEG(const px::Point2D<int>& dim,
const int framerate,
const std::string& filename,
const std::string& filter_cmd);
~FFMPEG();
void add_frame(pxImage * const img);
void encode();
void cancel();
private:
void init_filters(); // Init everything that needed to filter the input frame.
void init_muxer(); // The muxer that creates the output file.
void muxing_one_frame(AVFrame* frame);
void release();
int _ret = 0; // status code from FFMPEG.
char _err_msg[FFMPEG_MSG_LEN]; // Error message buffer.
int m_width = 0; // The width that all futur images must have to be accepted.
int m_height = 0; // The height that all futur images must have to be accepted.
int m_framerate = 0; // GIF Framerate.
std::string m_filename = ""; // The GIF filename (on cache?)
std::string m_filter_desc = ""; // The FFMPEG filter to apply over the frames.
bool as_frame = false;
AVFrame* picture_rgb24 = nullptr; // Temporary frame that will hold the pxImage in an RGB24 format (NOTE: TOP-LEFT origin)
AVFormatContext* ofmt_ctx = nullptr; // ouput format context associated to the
AVCodecContext* o_codec_ctx = nullptr; // output codec for the GIF
AVFilterGraph* filter_graph = nullptr; // filter graph associate with the string we want to execute
AVFilterContext* buffersrc_ctx = nullptr; // The buffer that will store all the frames in one place for the palette generation.
AVFilterContext* buffersink_ctx = nullptr; // The buffer that will store the result afterward (once the palette are used).
int64_t m_pts_increment = 0;
};
};
};
ctor
px::GIF::FFMPEG::FFMPEG(const px::Point2D<int>& dim,
const int framerate,
const std::string& filename,
const std::string& filter_cmd) :
m_width(dim.x()),
m_height(dim.y()),
m_framerate(framerate),
m_filename(filename),
m_filter_desc(filter_cmd)
{
#if !_DEBUG
av_log_set_level(AV_LOG_QUIET); // Set the FFMPEG log to quiet to avoid too much logs.
#endif
// Allocate the temporary buffer that hold the ffmpeg image (pxImage to AVFrame conversion).
picture_rgb24 = av_frame_alloc();
picture_rgb24->pts = 0;
picture_rgb24->data[0] = NULL;
picture_rgb24->linesize[0] = -1;
picture_rgb24->format = AV_PIX_FMT_RGB24;
picture_rgb24->height = m_height;
picture_rgb24->width = m_width;
if ((_ret = av_image_alloc(picture_rgb24->data, picture_rgb24->linesize, m_width, m_height, (AVPixelFormat)picture_rgb24->format, 24)) < 0)
throw px::GIF::Error("Failed to allocate the AVFrame for pxImage conversion with error: " +
std::string(av_make_error_string(_err_msg, FFMPEG_MSG_LEN, _ret)),
"GIF::FFMPEG CTOR");
//printf("allocated picture of size %d, linesize %d %d %d %d\n", _ret, picture_rgb24->linesize[0], picture_rgb24->linesize[1], picture_rgb24->linesize[2], picture_rgb24->linesize[3]);
init_muxer(); // Prepare the GIF encoder (open it on disk).
init_filters(); // Prepare the filter that will be applied over the frame.
// Instead of hardcoder {1,100} which is the GIF tbn, we collect it from its stream.
// This will avoid future problem if the codec change in ffmpeg.
if (ofmt_ctx && ofmt_ctx->nb_streams > 0)
m_pts_increment = av_rescale_q(1, { 1, m_framerate }, ofmt_ctx->streams[0]->time_base);
else
m_pts_increment = av_rescale_q(1, { 1, m_framerate }, { 1, 100 });
}
FFMPEG初始化（过滤器和多路复用器）
void px::GIF::FFMPEG::init_filters()
{
const AVFilter* buffersrc = avfilter_get_by_name("buffer");
const AVFilter* buffersink = avfilter_get_by_name("buffersink");
AVRational time_base = { 1, m_framerate };
AVRational aspect_pixel = { 1, 1 };
AVFilterInOut* inputs = avfilter_inout_alloc();
AVFilterInOut* outputs = avfilter_inout_alloc();
filter_graph = avfilter_graph_alloc();
try
{
if (!outputs || !inputs || !filter_graph)
throw px::GIF::Error("Failed to 'init_filters' could not allocated the graph/filters.", "GIF::FFMPEG init_filters");
char args[512];
snprintf(args, sizeof(args),
"video_size=%dx%d:pix_fmt=%d:time_base=%d/%d:pixel_aspect=%d/%d",
m_width, m_height,
picture_rgb24->format,
time_base.num, time_base.den,
aspect_pixel.num, aspect_pixel.den);
if (avfilter_graph_create_filter(&buffersrc_ctx, buffersrc, "in", args, nullptr, filter_graph) < 0)
throw px::GIF::Error("Failed to create the 'source buffer' in init_filer method.", "GIF::FFMPEG init_filters");
if (avfilter_graph_create_filter(&buffersink_ctx, buffersink, "out", nullptr, nullptr, filter_graph) < 0)
throw px::GIF::Error("Failed to create the 'sink buffer' in init_filer method.", "GIF::FFMPEG init_filters");
// GIF has possible output of PAL8.
enum AVPixelFormat pix_fmts[] = { AV_PIX_FMT_PAL8, AV_PIX_FMT_NONE };
if (av_opt_set_int_list(buffersink_ctx, "pix_fmts", pix_fmts, AV_PIX_FMT_NONE, AV_OPT_SEARCH_CHILDREN) < 0)
throw px::GIF::Error("Failed to set the output pixel format.", "GIF::FFMPEG init_filters");
outputs->name = av_strdup("in");
outputs->filter_ctx = buffersrc_ctx;
outputs->pad_idx = 0;
outputs->next = nullptr;
inputs->name = av_strdup("out");
inputs->filter_ctx = buffersink_ctx;
inputs->pad_idx = 0;
inputs->next = nullptr;
// GIF has possible output of PAL8.
if (avfilter_graph_parse_ptr(filter_graph, m_filter_desc.c_str(), &inputs, &outputs, nullptr) < 0)
throw px::GIF::Error("Failed to parse the filter graph (bad string!).", "GIF::FFMPEG init_filters");
if (avfilter_graph_config(filter_graph, nullptr) < 0)
throw px::GIF::Error("Failed to configure the filter graph (bad string!).", "GIF::FFMPEG init_filters");
avfilter_inout_free(&inputs);
avfilter_inout_free(&outputs);
}
catch (const std::exception& e)
{
// Catch exception to delete element.
avfilter_inout_free(&inputs);
avfilter_inout_free(&outputs);
throw e; // re-throuw
}
}
void px::GIF::FFMPEG::init_muxer()
{
AVOutputFormat* o_fmt = av_guess_format("gif", m_filename.c_str(), "video/gif");
if ((_ret = avformat_alloc_output_context2(&ofmt_ctx, o_fmt, "gif", m_filename.c_str())) < 0)
throw px::GIF::Error(std::string(av_make_error_string(_err_msg, FFMPEG_MSG_LEN, _ret)) + " allocate output format.", "GIF::FFMPEG init_muxer");
AVCodec* codec = avcodec_find_encoder(AV_CODEC_ID_GIF);
if (!codec) throw px::GIF::Error("Could to find the 'GIF' codec.", "GIF::FFMPEG init_muxer");
#if 0
const AVPixelFormat* p = codec->pix_fmts;
while (p != NULL && *p != AV_PIX_FMT_NONE) {
printf("supported pix fmt: %s\n", av_get_pix_fmt_name(*p));
++p;
}
#endif
AVStream* stream = avformat_new_stream(ofmt_ctx, codec);
AVCodecParameters* codec_paramters = stream->codecpar;
codec_paramters->codec_tag = 0;
codec_paramters->codec_id = codec->id;
codec_paramters->codec_type = AVMEDIA_TYPE_VIDEO;
codec_paramters->width = m_width;
codec_paramters->height = m_height;
codec_paramters->format = AV_PIX_FMT_PAL8;
o_codec_ctx = avcodec_alloc_context3(codec);
avcodec_parameters_to_context(o_codec_ctx, codec_paramters);
o_codec_ctx->time_base = { 1, m_framerate };
if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
o_codec_ctx->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;
if ((_ret = avcodec_open2(o_codec_ctx, codec, NULL)) < 0)
throw px::GIF::Error(std::string(av_make_error_string(_err_msg, FFMPEG_MSG_LEN, _ret)) + " open output codec.", "GIF::FFMPEG init_muxer");
if ((_ret = avio_open(&ofmt_ctx->pb, m_filename.c_str(), AVIO_FLAG_WRITE)) < 0)
throw px::GIF::Error(std::string(av_make_error_string(_err_msg, FFMPEG_MSG_LEN, _ret)) + " avio open error.", "GIF::FFMPEG init_muxer");
if ((_ret = avformat_write_header(ofmt_ctx, NULL)) < 0)
throw px::GIF::Error(std::string(av_make_error_string(_err_msg, FFMPEG_MSG_LEN, _ret)) + " write GIF header", "GIF::FFMPEG init_muxer");
#if _DEBUG
// This print the stream/output format.
av_dump_format(ofmt_ctx, -1, m_filename.c_str(), 1);
#endif
}
添加帧（通常是在循环中）
void px::GIF::FFMPEG::add_frame(pxImage * const img)
{
if (img->getImageType() != PXT_BYTE || img->getNChannels() != 4)
throw px::GIF::Error("Failed to 'add_frame' since image is not PXT_BYTE and 4-channels.", "GIF::FFMPEG add_frame");
if (img->getWidth() != m_width || img->getHeight() != m_height)
throw px::GIF::Error("Failed to 'add_frame' since the size is not same to other inputs.", "GIF::FFMPEG add_frame");
const int pitch = picture_rgb24->linesize[0];
auto px_ptr = getImageAccessor<pxUChar_C4>(img);
for (int y = 0; y < m_height; y++)
{
const int px_row = img->getOrigin() == ORIGIN_BOT_LEFT ? m_height - y - 1 : y;
for (int x = 0; x < m_width; x++)
{
const int idx = y * pitch + 3 * x;
picture_rgb24->data[0][idx] = px_ptr[px_row][x].ch[PX_RE];
picture_rgb24->data[0][idx + 1] = px_ptr[px_row][x].ch[PX_GR];
picture_rgb24->data[0][idx + 2] = px_ptr[px_row][x].ch[PX_BL];
}
}
// palettegen need a whole stream, just add frame to buffer.
if ((_ret = av_buffersrc_add_frame_flags(buffersrc_ctx, picture_rgb24, AV_BUFFERSRC_FLAG_KEEP_REF)) < 0)
throw px::GIF::Error("Failed to 'add_frame' to global buffer with error: " +
std::string(av_make_error_string(_err_msg, FFMPEG_MSG_LEN, _ret)),
"GIF::FFMPEG add_frame");
// Increment the FPS of the picture for the next add-up to the buffer.
picture_rgb24->pts += m_pts_increment;
as_frame = true;
}
编码器（最后一步）
void px::GIF::FFMPEG::encode()
{
if (!as_frame)
throw px::GIF::Error("Please 'add_frame' before running the Encoding().", "GIF::FFMPEG encode");
// end of buffer
if ((_ret = av_buffersrc_add_frame_flags(buffersrc_ctx, nullptr, AV_BUFFERSRC_FLAG_KEEP_REF)) < 0)
throw px::GIF::Error("error add frame to buffer source: " + std::string(av_make_error_string(_err_msg, FFMPEG_MSG_LEN, _ret)), "GIF::FFMPEG encode");
do {
AVFrame* filter_frame = av_frame_alloc();
_ret = av_buffersink_get_frame(buffersink_ctx, filter_frame);
if (_ret == AVERROR(EAGAIN) || _ret == AVERROR_EOF) {
av_frame_unref(filter_frame);
break;
}
// write the filter frame to output file
muxing_one_frame(filter_frame);
av_frame_unref(filter_frame);
} while (_ret >= 0);
av_write_trailer(ofmt_ctx);
}
void px::GIF::FFMPEG::muxing_one_frame(AVFrame* frame)
{
int ret = avcodec_send_frame(o_codec_ctx, frame);
AVPacket *pkt = av_packet_alloc();
av_init_packet(pkt);
while (ret >= 0) {
ret = avcodec_receive_packet(o_codec_ctx, pkt);
if (ret == AVERROR(EAGAIN) || ret == AVERROR_EOF) {
break;
}
av_write_frame(ofmt_ctx, pkt);
}
av_packet_unref(pkt);
}
DTOR，释放并取消
px::GIF::FFMPEG::~FFMPEG()
{
release();
}
void px::GIF::FFMPEG::release()
{
// Muxer stuffs
if (ofmt_ctx != nullptr) avformat_free_context(ofmt_ctx);
if (o_codec_ctx != nullptr) avcodec_close(o_codec_ctx);
if (o_codec_ctx != nullptr) avcodec_free_context(&o_codec_ctx);
ofmt_ctx = nullptr;
o_codec_ctx = nullptr;
// Filter stuffs
if (buffersrc_ctx != nullptr) avfilter_free(buffersrc_ctx);
if (buffersink_ctx != nullptr) avfilter_free(buffersink_ctx);
if (filter_graph != nullptr) avfilter_graph_free(&filter_graph);
buffersrc_ctx = nullptr;
buffersink_ctx = nullptr;
filter_graph = nullptr;
// Conversion image.
if (picture_rgb24 != nullptr) av_frame_free(&picture_rgb24);
picture_rgb24 = nullptr;
}
void px::GIF::FFMPEG::cancel()
{
// In-case of failure we must close ffmpeg and exit.
av_write_trailer(ofmt_ctx);
// Release and close all elements.
release();
// Delete the file on disk.
if (remove(m_filename.c_str()) != 0)
PX_LOG0(PX_LOGLEVEL_ERROR, "GIF::FFMPEG - On 'cancel' failed to remove the file.");
}
花了我一段时间，但终于明白了！
我在我的取消方法中缺少一个avio_close(ofmt_ctx->pb);。
一旦从ffmpeg释放文件，std::remove()就像一个超级按钮。
注意，只有在成功执行av_write_trailer时才应调用avio_close和init_muxer，因此我有一个成员变量来标记成功与否。然后，我在取消中进行适当的调用。