增加FFmpegEncoder和test_audio_transcode, 主要修改有:

- 使用FFmpegAudioFifo来简化代码
- 修复转码时间戳不规则递增，导致的音频破音和不连续问题
- 使用double来保存_tsp，避免出现2.5ms的frame_size(ffmpeg内置的opus)

tests/test_audio_transcode.cpp

@@ -0,0 +1,118 @@
+#include "Codec/Transcode.h"
+#include "Record/MP4Demuxer.h"
+#include "Record/MP4Muxer.h"
+#include "Extension/AAC.h"
+#include "Extension/Opus.h"
+#include "Extension/G711.h"
+#include "Util/logger.h"
+using namespace mediakit;
+struct TransCtx {
+    using Ptr = std::shared_ptr<TransCtx>;
+    TransCtx(const char *prefix, CodecId codec) {
+        char path[256];
+        Track::Ptr track;
+        switch (codec) {
+        case CodecAAC:
+            track.reset(new AACTrack(44100, 1));
+            sprintf(path, "%s_aac.mp4", prefix);
+            break;
+        case CodecOpus:
+            track.reset(new OpusTrack());
+            sprintf(path, "%s_opus.mp4", prefix);
+            break;
+        case CodecG711A:
+        case CodecG711U:
+            track.reset(new G711Track(codec, 8000, 1, 16));
+            sprintf(path, "%s_711%c.mp4", prefix, codec == CodecG711A ? 'A' : 'U');
+            break;
+        default:
+            return;
+            break;
+        }
+        file.reset(new MP4Muxer());
+        file->openMP4(path);
+        file->addTrack(track);
+        enc.reset(new FFmpegEncoder(track));
+        enc->setOnEncode([this](const Frame::Ptr &frame) { file->inputFrame(frame); });
+    }
+    ~TransCtx() {
+        enc = nullptr;
+        file = nullptr;
+    }
+    void inputFrame(const FFmpegFrame::Ptr &frame) { enc->inputFrame(frame, false); }
+    FFmpegEncoder::Ptr enc;
+    std::shared_ptr<MP4Muxer> file;
+};
+
+int TranscodeAudio(const char *srcPath, const char *dstPath) {
+    MP4Demuxer srcMp4;
+    srcMp4.openMP4(srcPath);
+
+    auto srcTrack = srcMp4.getTrack(TrackAudio);
+    if (!srcTrack) {
+        printf("unable to find audioTrack %s\n", srcPath);
+        return -1;
+    }
+    std::vector<TransCtx::Ptr> trans;
+    FFmpegDecoder audioDec(srcTrack);
+    auto dstCodec = getCodecId(dstPath);
+    if (!strcasecmp(dstPath, "aac"))
+        dstCodec = CodecAAC;
+    if (dstCodec != CodecInvalid) {
+        std::string dstFile(srcPath);
+        auto pos = dstFile.rfind('_');
+        if (pos == dstFile.npos)
+            pos = dstFile.rfind('.');
+        if (pos != dstFile.npos)
+            dstFile = dstFile.substr(0, pos);
+        if (dstCodec == srcTrack->getCodecId()) {
+            printf("same codec %s, skip transcode\n", dstPath);
+            return 0;
+        }
+        trans.push_back(std::make_shared<TransCtx>(dstFile.c_str(), dstCodec));
+    }
+    else {
+        for (auto codec : { CodecAAC, CodecOpus, CodecG711A, CodecG711U }) {
+            if (codec == srcTrack->getCodecId())
+                continue;
+            trans.push_back(std::make_shared<TransCtx>(dstPath, codec));
+        }
+    }
+    // srcTrack -> audioDec
+    srcTrack->addDelegate([&](const Frame::Ptr &frame) -> bool {
+        audioDec.inputFrame(frame, true, false, false);
+        return true;
+    });
+    // audioDec -> audioEnc
+    audioDec.setOnDecode([&](const FFmpegFrame::Ptr &frame) {
+        for (TransCtx::Ptr p : trans)
+            p->inputFrame(frame);
+    });
+    toolkit::Ticker tick;
+    printf("startReadMp4 %" PRIu64 "ms\n", srcMp4.getDurationMS());
+    bool key, eof;
+    Frame::Ptr frame;
+    while (true) {
+        // srcMp4->srcTrack
+        frame = srcMp4.readFrame(key, eof);
+        if (eof) {
+            printf("eof break loop, it tooks %" PRIu64 " ms\n", tick.elapsedTime());
+            break;
+        }
+    }
+    return 0;
+}
+
+int main(int argc, char *argv[]) {
+    if (argc != 3) {
+        printf("usage src.mp4 dst_prefix/codecName\n");
+        return 0;
+    }
+    toolkit::Logger::Instance().add(std::make_shared<toolkit::ConsoleChannel>());
+    try {
+        return TranscodeAudio(argv[1], argv[2]);
+    } catch (std::exception e) {
+        printf("exception: %s\n", e.what());
+        return -1;
+    }
+}