Feature: cut video with specific offset-time and duration

app/CMakeLists.txt

@@ -31,6 +31,7 @@ add_library( # Sets the name of the library.
             src/main/cpp/ffmpeg_pusher.cpp
             src/main/cpp/video_filter.c
             src/main/cpp/ffprobe_cmd.cpp
+            src/main/cpp/cut_video.cpp
             src/main/cpp/visualizer/fft.cpp
             src/main/cpp/visualizer/fixed_fft.cpp
             src/main/cpp/visualizer/block_queue.c

app/src/main/cpp/cut_video.cpp

@@ -0,0 +1,116 @@
+//
+// Created by xu fulong on 2022/5/13.
+//
+
+#include <cut_video.h>
+
+#ifdef __ANDROID__
+#include <android/log.h>
+#define LOGE(FORMAT, ...) __android_log_print(ANDROID_LOG_ERROR, "CutVideo", FORMAT, ##__VA_ARGS__)
+#else
+#include <stdio.h>
+#define LOGE(FORMAT, ...) printf(FORMAT, ##__VA_ARGS__)
+#endif
+
+int CutVideo::open_output_file(AVFormatContext *ifmt_ctx, const char *filename)
+{
+    int ret;
+    avformat_alloc_output_context2(&ofmt_ctx, nullptr, nullptr, filename);
+    if (!ofmt_ctx) {
+        LOGE("Could not create output context\n");
+        return AVERROR_UNKNOWN;
+    }
+
+    for (int i = 0; i < ifmt_ctx->nb_streams; i++) {
+        AVStream* in_stream = ifmt_ctx->streams[i];
+        AVCodecParameters* codecpar = in_stream->codecpar;
+
+        AVCodec* dec = avcodec_find_decoder(codecpar->codec_id);
+        AVStream* out_stream = avformat_new_stream(ofmt_ctx, dec);
+        if (!out_stream) {
+            LOGE("Failed allocating output stream\n");
+            ret = AVERROR_UNKNOWN;
+            return ret;
+        }
+        avcodec_parameters_copy(out_stream->codecpar, codecpar);
+    }
+
+    av_dump_format(ofmt_ctx, 0, filename, 1);
+    if (!(ofmt_ctx->oformat->flags & AVFMT_NOFILE)) {
+        ret = avio_open(&ofmt_ctx->pb, filename, AVIO_FLAG_WRITE);
+        if (ret < 0) {
+            LOGE("Could not open output file %s\n", filename);
+            return ret;
+        }
+    }
+    /* init muxer, write output file header */
+    ret = avformat_write_header(ofmt_ctx, nullptr);
+    if (ret < 0) {
+        LOGE("Error occurred when opening output file\n");
+        return ret;
+    }
+
+    return 0;
+}
+
+AVPacket* CutVideo::copy_packet(AVFormatContext *ifmt_ctx, AVPacket *packet) {
+    AVStream* in_stream;
+    AVStream* out_stream;
+    auto* pkt = (AVPacket*)av_malloc(sizeof(AVPacket));
+    av_new_packet(pkt, 0);
+    if (0 == av_packet_ref(pkt, packet)) {
+        in_stream  = ifmt_ctx->streams[pkt->stream_index];
+        out_stream = ofmt_ctx->streams[pkt->stream_index];
+        // 转换pts与dts
+        pkt->pts = av_rescale_q_rnd(pkt->pts, in_stream->time_base, out_stream->time_base,
+                                    static_cast<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,
+                                    static_cast<AVRounding>(AV_ROUND_NEAR_INF |
+                                                            AV_ROUND_PASS_MINMAX));
+        pkt->duration = av_rescale_q(pkt->duration, in_stream->time_base, out_stream->time_base);
+        return pkt;
+    }
+    return nullptr;
+}
+
+int CutVideo::write_internal(AVFormatContext *ifmt_ctx, AVPacket *packet)
+{
+    int ret;
+    AVPacket *pkt = copy_packet(ifmt_ctx, packet);
+    if (pkt == nullptr) {
+        LOGE("packet is NULL\n");
+        return -1;
+    }
+    // sub the first timestamp offset
+    pkt->pts = pkt->pts - start_pts;
+    pkt->dts = pkt->dts - start_dts;
+    // write packet into file
+    if ((ret = av_interleaved_write_frame(ofmt_ctx, pkt)) < 0) {
+        LOGE("Error muxing packet\n");
+    }
+    av_packet_unref(pkt);
+    return ret;
+}
+
+void CutVideo::write_output_file(AVFormatContext *ifmt_ctx, AVPacket *packet) {
+    int64_t timestamp = packet->pts * av_q2d(ifmt_ctx->streams[packet->stream_index]->time_base);
+    if (timestamp >= start_time && timestamp < start_time + duration) {
+//        if (start_pts == 0 && start_dts == 0) {
+//            start_pts = packet->pts;
+//            start_dts = packet->dts;
+//        }
+        LOGE("write frame timestamp=%ld\n", timestamp);
+        write_internal(ifmt_ctx, packet);
+    }
+}
+
+void CutVideo::close_output_file() {
+    if (!ofmt_ctx)
+        return;
+    av_write_trailer(ofmt_ctx);
+    if (!(ofmt_ctx->oformat->flags & AVFMT_NOFILE)) {
+        avio_close(ofmt_ctx->pb);
+    }
+    avformat_free_context(ofmt_ctx);
+}

app/src/main/cpp/cut_video.h

@@ -0,0 +1,39 @@
+//
+// Created by xu fulong on 2022/5/13.
+//
+
+#ifndef CUT_VIDEO_H
+#define CUT_VIDEO_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+#include "libavformat/avformat.h"
+#ifdef __cplusplus
+}
+#endif
+
+class CutVideo {
+private:
+
+    int64_t start_time = 15;
+    int64_t duration   = 10;
+
+    int64_t start_dts = 0;
+    int64_t start_pts = 0;
+    AVFormatContext *ofmt_ctx = nullptr;
+
+    AVPacket* copy_packet(AVFormatContext *ifmt_ctx, AVPacket *packet);
+
+    int write_internal(AVFormatContext *ifmt_ctx, AVPacket *packet);
+
+public:
+
+    int open_output_file(AVFormatContext *ifmt_ctx, const char *filename);
+
+    void write_output_file(AVFormatContext *ifmt_ctx, AVPacket *packet);
+
+    void close_output_file();
+};
+
+#endif //CUT_VIDEO_H