134 lines
4.1 KiB
Markdown
134 lines
4.1 KiB
Markdown
# 1. ffmpeg开发文档
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## 1.1. ffplay命令使用
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* 播放G711a音频文件
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```code
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$ ffplay -i audio.g711a -f alaw -ac 1 -ar 8000
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```
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ffmpeg -i input.g711a -acodec alaw output.wav
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* 播放h264视频文件
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```code
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$ ffplay video.h264
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```
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* g711a音频文件转wav音频文件
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```code
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$ fmpeg -f mulaw -ar 8000 -i audio.g711a audio.wav
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```
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* 播放pcm文件
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```code
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$ ffplay -f s16le -ar 8000 -ac 1 test.pcm
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```
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* 生成jpeg
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```code
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$ ./ffmpeg -i test.h264 -vframes 1 -vf "scale=640:480:force_original_aspect_ratio=decrease" -f image2 output.jpeg
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```
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```code
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void FfmpegThumbnail::GetDecodeDataCallback(AVFrame *frame)
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{
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LogInfo("GetDecodeDataCallback frame->width = %d, frame->height = %d\n", frame->width, frame->height);
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// Allocate output frame for YUV420P format
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AVFrame *output_frame = av_frame_alloc();
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output_frame->format = AV_PIX_FMT_YUV420P;
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output_frame->width = 640;
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output_frame->height = 480;
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// Calculate buffer size for YUV420P
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int yuv_buf_size = av_image_get_buffer_size(AV_PIX_FMT_YUV420P, 640, 480, 1);
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uint8_t *yuv_buf = (uint8_t *)av_malloc(yuv_buf_size);
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// Fill output frame with YUV420P buffer
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av_image_fill_arrays(output_frame->data, output_frame->linesize, yuv_buf, AV_PIX_FMT_YUV420P, 640, 480, 1);
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// Create SwsContext for pixel format conversion from YUV420P (1920x2160) to YUV420P (640x480)
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SwsContext *sws_ctx = sws_getContext(frame->width, frame->height, static_cast<AVPixelFormat>(frame->format),
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output_frame->width, output_frame->height, AV_PIX_FMT_YUV420P,
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SWS_BILINEAR, nullptr, nullptr, nullptr);
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if (!sws_ctx) {
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LogError("Failed to create SwsContext for pixel format conversion\n");
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av_frame_free(&output_frame);
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av_free(yuv_buf);
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return;
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}
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// Perform pixel format conversion and scaling
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sws_scale(sws_ctx, frame->data, frame->linesize, 0, frame->height,
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output_frame->data, output_frame->linesize);
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// Clean up SwsContext
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sws_freeContext(sws_ctx);
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// Encode the YUV420P frame to JPEG using mEncoder
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if (mEncoder) {
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mEncoder->EncodeData(output_frame, mStream, mEncodeCallback);
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}
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// Free allocated resources
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av_frame_free(&output_frame);
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av_free(yuv_buf);
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}
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```
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* 将h264和wav文件合成mp4文件
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**注意：未发现可以将h264和g711a文件合成mp4文件**
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```code
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$ ffmpeg -i video.h264 -i audio.wav -c:v copy -c:a aac -b:a 96k test.mp4
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```
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## 1.2. 问题记录
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### 1.2.1. avformat_open_input 执行失败
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  在执行avformat_open_input时，返回-1094995529<0，错误
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解决：在Ubuntu编译时，使能所有的编译选项，并且把--arch=赋值为linux
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```code
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# 详见：//external/ffmpeg/CMakeLists.txt
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set(CONFIGURE_COMMAND "--enable-cross-compile --target-os=linux --arch=linux \
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--cc=${CMAKE_C_COMPILER} \
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--cxx=${CMAKE_CXX_COMPILER} \
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--prefix=${EXTERNAL_LIBS_OUTPUT_PATH}/ffmpeg \
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--enable-parsers --enable-decoder=h264 \
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--enable-ffmpeg --enable-shared --enable-static \
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--enable-gpl --enable-nonfree --enable-version3 --enable-small \
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--enable-muxer=mov --enable-muxer=mp4 \
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--enable-decoder=aac \
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--enable-demuxer=mov \
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--enable-protocol=file --enable-bsf=aac_adtstoasc --enable-bsf=h264_mp4toannexb --enable-bsf=hevc_mp4toannexb")
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```
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### 1.2.2. avformat_open_input 执行失败
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  打开g711a文件时，提示无效数据。如下：
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**Invalid data found when processing input**
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解决：
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调用 avformat_open_input 函数时，指定输入文件的格式（第三个参数），g711a文件格式为：alaw。
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```code
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# //utils/MediaBase/src/MediaBaseImpl.cpp
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const AVInputFormat *iformat = av_find_input_format(InputFormat(mType));
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AVFormatContext *pFormatCtx = nullptr;
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if ((result = avformat_open_input(&pFormatCtx, path.c_str(), iformat, nullptr)) < 0) {
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char error_str[AV_ERROR_MAX_STRING_SIZE] = {0};
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av_make_error_string(error_str, AV_ERROR_MAX_STRING_SIZE, result);
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LogError("Couldn't open file: %s, result=%s\n", path.c_str(), error_str);
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return CreateStatusCode(STATUS_CODE_NOT_OK);
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}
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```
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