# 1. ffmpeg开发文档

## 1.1. ffplay命令使用

* 播放G711a音频文件

```code
$ ffplay -i audio.g711a -f alaw -ac 1 -ar 8000
```
ffmpeg -i input.g711a -acodec alaw output.wav

* 播放h264视频文件

```code
$ ffplay video.h264
```

* g711a音频文件转wav音频文件

```code
$ fmpeg -f mulaw -ar 8000 -i audio.g711a audio.wav
```

* 播放pcm文件

```code
$ ffplay -f s16le -ar 8000 -ac 1 test.pcm
```

* 生成jpeg

```code
$ ./ffmpeg -i test.h264 -vframes 1 -vf "scale=640:480:force_original_aspect_ratio=decrease" -f image2 output.jpeg
```

```code
void FfmpegThumbnail::GetDecodeDataCallback(AVFrame *frame)
{
    LogInfo("GetDecodeDataCallback frame->width = %d, frame->height = %d\n", frame->width, frame->height);

    // Allocate output frame for YUV420P format
    AVFrame *output_frame = av_frame_alloc();
    output_frame->format = AV_PIX_FMT_YUV420P;
    output_frame->width = 640;
    output_frame->height = 480;

    // Calculate buffer size for YUV420P
    int yuv_buf_size = av_image_get_buffer_size(AV_PIX_FMT_YUV420P, 640, 480, 1);
    uint8_t *yuv_buf = (uint8_t *)av_malloc(yuv_buf_size);

    // Fill output frame with YUV420P buffer
    av_image_fill_arrays(output_frame->data, output_frame->linesize, yuv_buf, AV_PIX_FMT_YUV420P, 640, 480, 1);

    // Create SwsContext for pixel format conversion from YUV420P (1920x2160) to YUV420P (640x480)
    SwsContext *sws_ctx = sws_getContext(frame->width, frame->height, static_cast<AVPixelFormat>(frame->format),
                                         output_frame->width, output_frame->height, AV_PIX_FMT_YUV420P,
                                         SWS_BILINEAR, nullptr, nullptr, nullptr);
    if (!sws_ctx) {
        LogError("Failed to create SwsContext for pixel format conversion\n");
        av_frame_free(&output_frame);
        av_free(yuv_buf);
        return;
    }

    // Perform pixel format conversion and scaling
    sws_scale(sws_ctx, frame->data, frame->linesize, 0, frame->height,
              output_frame->data, output_frame->linesize);

    // Clean up SwsContext
    sws_freeContext(sws_ctx);

    // Encode the YUV420P frame to JPEG using mEncoder
    if (mEncoder) {
        mEncoder->EncodeData(output_frame, mStream, mEncodeCallback);
    }

    // Free allocated resources
    av_frame_free(&output_frame);
    av_free(yuv_buf);
}

```

* 将h264和wav文件合成mp4文件

**注意：未发现可以将h264和g711a文件合成mp4文件**

```code
$ ffmpeg -i video.h264 -i audio.wav -c:v copy -c:a aac -b:a 96k test.mp4
```

## 1.2. 问题记录

### 1.2.1. avformat_open_input 执行失败

&emsp;&emsp;在执行avformat_open_input时，返回-1094995529<0，错误

解决：在Ubuntu编译时，使能所有的编译选项，并且把--arch=赋值为linux

```code
# 详见：//external/ffmpeg/CMakeLists.txt
set(CONFIGURE_COMMAND "--enable-cross-compile --target-os=linux --arch=linux \
--cc=${CMAKE_C_COMPILER} \
--cxx=${CMAKE_CXX_COMPILER} \
--prefix=${EXTERNAL_LIBS_OUTPUT_PATH}/ffmpeg \
--enable-parsers --enable-decoder=h264 \
--enable-ffmpeg --enable-shared --enable-static \
--enable-gpl --enable-nonfree --enable-version3 --enable-small \
--enable-muxer=mov --enable-muxer=mp4 \
--enable-decoder=aac \
--enable-demuxer=mov \
--enable-protocol=file --enable-bsf=aac_adtstoasc --enable-bsf=h264_mp4toannexb --enable-bsf=hevc_mp4toannexb")
```

### 1.2.2. avformat_open_input 执行失败

&emsp;&emsp;打开g711a文件时，提示无效数据。如下：
**Invalid data found when processing input**

解决：
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。

```code
# //utils/MediaBase/src/MediaBaseImpl.cpp
const AVInputFormat *iformat = av_find_input_format(InputFormat(mType));
AVFormatContext *pFormatCtx = nullptr;
if ((result = avformat_open_input(&pFormatCtx, path.c_str(), iformat, nullptr)) < 0) {
    char error_str[AV_ERROR_MAX_STRING_SIZE] = {0};
    av_make_error_string(error_str, AV_ERROR_MAX_STRING_SIZE, result);
    LogError("Couldn't open file: %s, result=%s\n", path.c_str(), error_str);
    return CreateStatusCode(STATUS_CODE_NOT_OK);
}
```