过去几周我一直在努力使用ffmpeg API，因为我找不到清晰的文档，而且我也觉得很难搜索，因为我在网上找到的所有解决方案都不涉及c API而是ffmpeg.c命令行程序。我正在创建一个程序，需要从网络摄像头和音频中捕获视频，在屏幕上显示帧并将音频和帧记录到视频文件中。我也使用QT作为这个项目的框架。
我已经能够在屏幕上显示帧，甚至记录它们，但我的问题是音频和视频的记录。我决定创建一个更简单的测试程序，它只将流保存到文件而不在屏幕上显示框架，从ffmpeg文档的remuxing.c example开始。我的代码如下：
//This is the variables on the .h
AVOutputFormat *ofmt;
AVFormatContext *ifmt_ctx, *ofmt_ctx;
QString cDeviceName;
QString aDeviceName;
int audioStream, videoStream;
bool done;
//The .cpp
#include "cameratest.h"
#include <QtConcurrent/QtConcurrent>
#include <QDebug>
CameraTest::CameraTest(QString cDeviceName, QString aDeviceName, QObject *parent) :
QObject(parent)
{
done = false;
this->cDeviceName = cDeviceName;
this->aDeviceName = aDeviceName;
av_register_all();
avdevice_register_all();
}
void CameraTest::toggleDone() {
done = !done;
}
int CameraTest::init() {
ofmt = NULL;
ifmt_ctx = NULL;
ofmt_ctx = NULL;
QString fullDName = cDeviceName.prepend("video=") + ":" + aDeviceName.prepend("audio=");
qDebug() << fullDName;
AVInputFormat *fmt = av_find_input_format("dshow");
int ret, i;
if (avformat_open_input(&ifmt_ctx, fullDName.toUtf8().data(), fmt, NULL) < 0) {
fprintf(stderr, "Could not open input file '%s'", fullDName.toUtf8().data());
return -1;
}
if ((ret = avformat_find_stream_info(ifmt_ctx, 0)) < 0) {
fprintf(stderr, "Failed to retrieve input stream information");
return -1;
}
av_dump_format(ifmt_ctx, 0, fullDName.toUtf8().data(), 0);
avformat_alloc_output_context2(&ofmt_ctx, NULL, NULL, "test.avi");
if (!ofmt_ctx) {
fprintf(stderr, "Could not create output context\n");
ret = AVERROR_UNKNOWN;
return -1;
}
ofmt = ofmt_ctx->oformat;
for (i = 0; i < ifmt_ctx->nb_streams; i++) {
AVStream *in_stream = ifmt_ctx->streams[i];
AVStream *out_stream = avformat_new_stream(ofmt_ctx, in_stream->codec->codec);
if (ifmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
videoStream = i;
}
else if (ifmt_ctx->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO) {
audioStream = i;
}
if (!out_stream) {
fprintf(stderr, "Failed allocating output stream\n");
ret = AVERROR_UNKNOWN;
return -1;
}
ret = avcodec_copy_context(out_stream->codec, in_stream->codec);
if (ret < 0) {
fprintf(stderr, "Failed to copy context from input to output stream codec context\n");
return -1;
}
out_stream->codec->codec_tag = 0;
if (ofmt_ctx->oformat->flags & AVFMT_GLOBALHEADER)
out_stream->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;
}
av_dump_format(ofmt_ctx, 0, "test.avi", 1);
if (!(ofmt->flags & AVFMT_NOFILE)) {
ret = avio_open(&ofmt_ctx->pb, "test.avi", AVIO_FLAG_WRITE);
if (ret < 0) {
fprintf(stderr, "Could not open output file '%s'", "test.avi");
return -1;
}
}
ret = avformat_write_header(ofmt_ctx, NULL);
if (ret < 0) {
fprintf(stderr, "Error occurred when opening output file\n");
return -1;
}
QtConcurrent::run(this, &CameraTest::grabFrames);
return 0;
}
void CameraTest::grabFrames() {
AVPacket pkt;
int ret;
while (av_read_frame(ifmt_ctx, &pkt) >= 0) {
AVStream *in_stream, *out_stream;
in_stream = ifmt_ctx->streams[pkt.stream_index];
out_stream = ofmt_ctx->streams[pkt.stream_index];
/* copy packet */
pkt.pts = av_rescale_q_rnd(pkt.pts, in_stream->time_base, out_stream->time_base, (AVRounding) (AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
pkt.dts = av_rescale_q_rnd(pkt.dts, in_stream->time_base, out_stream->time_base, (AVRounding) (AV_ROUND_NEAR_INF|AV_ROUND_PASS_MINMAX));
pkt.duration = av_rescale_q(pkt.duration, in_stream->time_base, out_stream->time_base);
pkt.pos = -1;
int ret = av_interleaved_write_frame(ofmt_ctx, &pkt);
if (ret < 0) {
qDebug() << "Error muxing packet";
//break;
}
av_free_packet(&pkt);
if(done) break;
}
av_write_trailer(ofmt_ctx);
avformat_close_input(&ifmt_ctx);
/* close output */
if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE))
avio_close(ofmt_ctx->pb);
avformat_free_context(ofmt_ctx);
if (ret < 0 && ret != AVERROR_EOF) {
//return -1;
//fprintf(stderr, "Error occurred: %s\n", av_err2str(ret));
}
}
av_interleaved_write_frame会返回视频数据包的错误。结束文件只显示第一帧，但音频似乎没问题。
在控制台上，这是打印的内容：
Input #0, dshow, from 'video=Integrated Camera:audio=Microfone interno (Conexant 206':
Duration: N/A, start: 146544.738000, bitrate: 1411 kb/s
Stream #0:0: Video: rawvideo, bgr24, 640x480, 30 tbr, 10000k tbn, 30 tbc
Stream #0:1: Audio: pcm_s16le, 44100 Hz, 2 channels, s16, 1411 kb/s
Output #0, avi, to 'test.avi':
Stream #0:0: Video: rawvideo, bgr24, 640x480, q=2-31, 30 tbc
Stream #0:1: Audio: pcm_s16le, 44100 Hz, 2 channels, s16, 1411 kb/s
[avi @ 0089f660] Using AVStream.codec.time_base as a timebase hint to the muxer is deprecated. Set AVStream.time_base instead.
[avi @ 0089f660] Using AVStream.codec.time_base as a timebase hint to the muxer is deprecated. Set AVStream.time_base instead.
[avi @ 0089f660] Application provided invalid, non monotonically increasing dts to muxer in stream 0: 4396365 >= 4396365
[avi @ 0089f660] Too large number of skipped frames 4396359 > 60000
[avi @ 0089f660] Too large number of skipped frames 4396360 > 60000
[avi @ 0089f660] Application provided invalid, non monotonically increasing dts to muxer in stream 0: 4396390 >= 4396390
[avi @ 0089f660] Too large number of skipped frames 4396361 > 60000
[avi @ 0089f660] Too large number of skipped frames 4396362 > 60000
[avi @ 0089f660] Too large number of skipped frames 4396364 > 60000
[avi @ 0089f660] Too large number of skipped frames 4396365 > 60000
[avi @ 0089f660] Too large number of skipped frames 4396366 > 60000
[avi @ 0089f660] Too large number of skipped frames 4396367 > 60000
在我看来，这似乎是一个需要解决的简单问题，但我真的对ffmpeg API一无所知，如果有人能引导我走向正确的方向那就太棒了！
谢谢！
答案 0 :(得分：2)
你的问题似乎有点特定于DirectShow。不幸的是，我没有访问DirectShow系统，但从症状看起来捕获不是你的问题。有什么问题是复用部分。可能是AVI不直接支持视频数据包的格式，也可能是数据包上的时间戳被破坏。
我会推荐一些你应该尝试的东西，一次一个：
av_write_frame代替av_interleaved_write_frame。grabFrames中获取原始视频数据包并将其转储到文件中。这应该给你一个可以通过ffplay播放的文件。 （您可能必须在ffplay命令中指定分辨率，像素格式和格式。）demuxing_decoding.c和decoding_encoding.c。这应该给你一个合适的视频文件。 （在大多数玩家中都可玩。）我对DirectShow一无所知，我不知道你的用例。所以我的建议主要关注FFmpeg API。其中一些可能过度/可能无法做你想做的事。