# Media Data Muxing

You can call the native APIs provided by the AVMuxer module to mux audio and video streams, that is, to store encoded audio and video data to a file in a certain format.

For details about the supported muxing formats, see [AVCodec Supported Formats](avcodec-support-formats.md#media-data-muxing).

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**Usage Scenario**

- Video and audio recording
  
  After you encode audio and video streams, mux them into files.

- Audio and video editing
  
  After you edit audio and video, mux them into files.

- Audio and video transcoding

  After you transcode audio and video, mux them into files.

## How to Develop

Read [AVMuxer](../../reference/apis-avcodec-kit/_a_v_muxer.md) for the API reference.

> **NOTE**
>
> To call the AVMuxer module to write a local file, request the **ohos.permission.READ_MEDIA** and **ohos.permission.WRITE_MEDIA** permissions by following the instructions provided in [Requesting User Authorization](../../security/AccessToken/request-user-authorization.md).

### Linking the Dynamic Library in the CMake Script

``` cmake
target_link_libraries(sample PUBLIC libnative_media_avmuxer.so)
target_link_libraries(sample PUBLIC libnative_media_core.so)
```

### How to Develop

The following walks you through how to implement the entire process of audio and video muxing. It uses the MP4 format as an example.

1. Add the header files.

   ```c++
   #include <multimedia/player_framework/native_avmuxer.h>
   #include <multimedia/player_framework/native_avcodec_base.h>
   #include <multimedia/player_framework/native_avformat.h>
   #include <multimedia/player_framework/native_avbuffer.h>
   #include <fcntl.h>
   ```

2. Call **OH_AVMuxer_Create()** to create an **OH_AVMuxer** instance.

   ```c++
   // Set the muxing format to MP4.
   OH_AVOutputFormat format = AV_OUTPUT_FORMAT_MPEG_4;
   // Create a File Descriptor (FD) in read/write mode.
   int32_t fd = open("test.mp4", O_CREAT | O_RDWR | O_TRUNC, S_IRUSR | S_IWUSR);
   OH_AVMuxer *muxer = OH_AVMuxer_Create(fd, format);
   ```

3. (Optional) Call **OH_AVMuxer_SetRotation()** to set the rotation angle.

   ```c++
   // Set the rotation angle when a video image needs to be rotated.
   OH_AVMuxer_SetRotation(muxer, 0);
   ```

4. Add an audio track.

   **Method 1: Use OH_AVFormat_Create to create the format.**

   ```c++
   int audioTrackId = -1;
   uint8_t *buffer = ...; // Encoding configuration data. If there is no configuration data, leave the parameter unspecified.
   size_t size =...; // Length of the encoding configuration data. Set this parameter based on project requirements.
   OH_AVFormat *formatAudio = OH_AVFormat_Create (); // Call OH_AVFormat_Create to create a format. The following showcases how to mux an AAC-LC audio with the sampling rate of 44100 Hz and two audio channels.
   OH_AVFormat_SetStringValue(formatAudio, OH_MD_KEY_CODEC_MIME, OH_AVCODEC_MIMETYPE_AUDIO_AAC); // Mandatory.
   OH_AVFormat_SetIntValue(formatAudio, OH_MD_KEY_AUD_SAMPLE_RATE, 44100); // Mandatory.
   OH_AVFormat_SetIntValue(formatAudio, OH_MD_KEY_AUD_CHANNEL_COUNT, 2); // Mandatory.
   OH_AVFormat_SetIntValue(formatAudio, OH_MD_KEY_PROFILE, AAC_PROFILE_LC); // Optional.
   OH_AVFormat_SetBuffer(formatAudio, OH_MD_KEY_CODEC_CONFIG, buffer, size); // Optional.
   
   int ret = OH_AVMuxer_AddTrack(muxer, &audioTrackId, formatAudio);
   if (ret != AV_ERR_OK || audioTrackId < 0) {
       // Failure to add the audio track.
   }
   OH_AVFormat_Destroy (formatAudio); // Destroy the format.
   ```

   **Method 2: Use OH_AVFormat_CreateAudioFormat to create the format.**

   ```c++
   int audioTrackId = -1;
   uint8_t *buffer = ...; // Encoding configuration data. If there is no configuration data, leave the parameter unspecified.
   size_t size =...; // Length of the encoding configuration data. Set this parameter based on project requirements.
   OH_AVFormat *formatAudio = OH_AVFormat_CreateAudioFormat(OH_AVCODEC_MIMETYPE_AUDIO_AAC, 44100, 2);
   OH_AVFormat_SetIntValue(formatAudio, OH_MD_KEY_PROFILE, AAC_PROFILE_LC); // Optional.
   OH_AVFormat_SetBuffer(formatAudio, OH_MD_KEY_CODEC_CONFIG, buffer, size); // Optional.
   
   int ret = OH_AVMuxer_AddTrack(muxer, &audioTrackId, formatAudio);
   if (ret != AV_ERR_OK || audioTrackId < 0) {
       // Failure to add the audio track.
   }
   OH_AVFormat_Destroy (formatAudio); // Destroy the format.
   ```

5. Add a video track.

   **Method 1: Use OH_AVFormat_Create to create the format.**

   ```c++
   int videoTrackId = -1;
   uint8_t *buffer = ...; // Encoding configuration data. If there is no configuration data, leave the parameter unspecified.
   size_t size =...; // Length of the encoding configuration data. Set this parameter based on project requirements.
   OH_AVFormat *formatVideo = OH_AVFormat_Create();
   OH_AVFormat_SetStringValue(formatVideo, OH_MD_KEY_CODEC_MIME, OH_AVCODEC_MIMETYPE_VIDEO_AVC); // Mandatory.
   OH_AVFormat_SetIntValue(formatVideo, OH_MD_KEY_WIDTH, 1280); // Mandatory.
   OH_AVFormat_SetIntValue(formatVideo, OH_MD_KEY_HEIGHT, 720); // Mandatory.
   OH_AVFormat_SetBuffer(formatVideo, OH_MD_KEY_CODEC_CONFIG, buffer, size); // Optional
   
   int ret = OH_AVMuxer_AddTrack(muxer, &videoTrackId, formatVideo);
   if (ret != AV_ERR_OK || videoTrackId < 0) {
       // Failure to add the video track.
   }
   OH_AVFormat_Destroy(formatVideo); // Destroy the format.
   ```

   **Method 2: Use OH_AVFormat_CreateVideoFormat to create the format.**

   ```c++
   int videoTrackId = -1;
   uint8_t *buffer = ...; // Encoding configuration data. If there is no configuration data, leave the parameter unspecified.
   size_t size =...; // Length of the encoding configuration data. Set this parameter based on project requirements.
   OH_AVFormat *formatVideo = OH_AVFormat_CreateVideoFormat(OH_AVCODEC_MIMETYPE_VIDEO_AVC, 1280, 720);
   OH_AVFormat_SetBuffer(formatVideo, OH_MD_KEY_CODEC_CONFIG, buffer, size); // Optional
   
   int ret = OH_AVMuxer_AddTrack(muxer, &videoTrackId, formatVideo);
   if (ret != AV_ERR_OK || videoTrackId < 0) {
       // Failure to add the video track.
   }
   OH_AVFormat_Destroy(formatVideo); // Destroy the format.
   ```

6. Add a cover track.

   **Method 1: Use OH_AVFormat_Create to create the format.**

   ```c++
   int coverTrackId = -1;
   OH_AVFormat *formatCover = OH_AVFormat_Create();
   OH_AVFormat_SetStringValue(formatCover, OH_MD_KEY_CODEC_MIME, OH_AVCODEC_MIMETYPE_IMAGE_JPG);
   OH_AVFormat_SetIntValue(formatCover, OH_MD_KEY_WIDTH, 1280);
   OH_AVFormat_SetIntValue(formatCover, OH_MD_KEY_HEIGHT, 720);
   
   int ret = OH_AVMuxer_AddTrack(muxer, &coverTrackId, formatCover);
   if (ret != AV_ERR_OK || coverTrackId < 0) {
       // Failure to add the cover track.
   }
   OH_AVFormat_Destroy(formatCover); // Destroy the format.
   ```

   **Method 2: Use OH_AVFormat_CreateVideoFormat to create the format.**

   ```c++
   int coverTrackId = -1;
   OH_AVFormat *formatCover = OH_AVFormat_CreateVideoFormat(OH_AVCODEC_MIMETYPE_IMAGE_JPG, 1280, 720);
   
   int ret = OH_AVMuxer_AddTrack(muxer, &coverTrackId, formatCover);
   if (ret != AV_ERR_OK || coverTrackId < 0) {
       // Failure to add the cover track.
   }
   OH_AVFormat_Destroy(formatCover); // Destroy the format.
   ```

7. Call **OH_AVMuxer_Start()** to start muxing.

   ```c++
   // Call Start() to write the file header. After this API is called, you cannot set media parameters or add tracks.
   if (OH_AVMuxer_Start(muxer) != AV_ERR_OK) {
       // Exception handling.
   }
   ```

8. Call **OH_AVMuxer_WriteSampleBuffer()** to write data. The encapsulated data includes video, audio, and cover data.

   ```c++
   // Data can be written only after Start() is called.
   int size = ...;
   OH_AVBuffer *sample = OH_AVBuffer_Create(size); // Create an AVBuffer instance.
   // Write data to the sample buffer by using OH_AVBuffer_GetAddr(sample). For details, see the usage of OH_AVBuffer.
   // Mux the cover. One image must be written at a time.
   
   // Set buffer information.
   OH_AVCodecBufferAttr info = {0};
   info.pts =...; // Playback start time of the current data, in microseconds. The relative time is used.
   info.size = size; // Length of the current data.
   info.offset = 0; // Offset. Generally, the value is 0.
   info.flags |= AVCODEC_BUFFER_FLAGS_SYNC_FRAME; // Flag of the current data. For details, see OH_AVCodecBufferFlags.
   info.flags |= AVCODEC_BUFFER_FLAGS_CODEC_DATA; // The AVC in annex-b format contains the codec configuration flag.
   OH_AVBuffer_SetBufferAttr(sample, &info); // Set the buffer attribute.
   int trackId = audioTrackId; // Select the audio or video track to be written.
   
   int ret = OH_AVMuxer_WriteSampleBuffer(muxer, trackId, sample);
   if (ret != AV_ERR_OK) {
       // Exception handling.
   }
   ```

9. Call **OH_AVMuxer_Stop()** to stop muxing.

   ```c++
   // Call Stop() to write the file trailer. After this API is called, you cannot write media data.
   if (OH_AVMuxer_Stop(muxer) != AV_ERR_OK) {
       // Exception handling.
   }
   ```

10. Call **OH_AVMuxer_Destroy()** to release the instance. Do not repeatedly destroy the instance. Otherwise, the program may crash.

    ```c++
    if (OH_AVMuxer_Destroy(muxer) != AV_ERR_OK) {
        // Exception handling.
    }
    muxer = NULL;
    close(fd); // Close the FD.
    ```