FFmpeg 内存输入&输出

[[N_FFmpeg]]
实例 内存输入/输出

ffmpeg内存编解码

内存输入

关键点就两个:

• 初始化AVIOContext时, 指定自定义的回调函数指针
  

1. //AVIOContext中的缓存
2. unsigned char* _iobuffer = (unsigned char*)av_malloc(40690);// 注意缓存容器要足够大
3. AVIOContext* avio = avio_alloc_context(_iobuffer , 40690 , 0 , this, fill_buffer,nullptr,nullptr);
4. assert( avio != NULL);
5. pFormatCtx->pb = avio;//给AVFormatContext
6. if(avformat_open_input(&pFormatCtx,NULL,NULL,NULL)!=0){
7.     printf("Couldn't open inputstream.(无法打开输入流)\n");
8.     return -1;
9. }

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• 回调函数
  

1. ///注意缓存 容器 要足够大
2. int fill_buffer(void * opaque,uint8_t *buf, int bufsize){
3.     SDKSource2Player *instance = static_cast<SDKSource2Player*>( opaque);
4.     callback_data * data =  instance->source2->takeDataPacketSync();
5.     memcpy( buf, data->data, data->size);//复制到容器 给 ffmpeg
6.     int size =  data->size;
7.     SDKSource2::destoryDataPacket(data);//销毁
8.     return size;
9.   }

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内存输出

• 回调函数
  

1. //内存输出数据
2. int fill_buffer_out(void * opaque, uint8_t *buf, int bufsize){
3.     WebSocketPlayer *instance = static_cast<WebSocketPlayer*>( opaque);
4.     instance->onAVPacketOutData(buf,bufsize );
5.    return bufsize;
6. }

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• 分配
  

1. // 内存输出
2. unsigned char* out_buffer = (unsigned char*)av_malloc(40690);//~40k
3. AVIOContext* out_avio = avio_alloc_context(out_buffer , 40690 , 1 , this, nullptr,nullptr,nullptr);
4. assert( out_avio != NULL);
5. AVOutputFormat *oformat = av_guess_format("mp4", nullptr, nullptr);
6. ret = avformat_alloc_output_context2(&outAvFormatCtx,oformat,nullptr,nullptr);
7. outAvFormatCtx->pb = out_avio;
8. outAvFormatCtx->flags = AVFMT_FLAG_CUSTOM_IO;

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• 踩坑指南
  

• 内存输出的时候需要注意 avio_alloc_context 的第三个参数 write_flag=1 表示 可写
  
• 输出 AVFormatContext 的flag 需要标记为 AVFMT_FLAG_CUSTOM_IO
  

1. ...
2. outAvFormatCtx->pb = out_avio;
3. outAvFormatCtx->flags = AVFMT_FLAG_CUSTOM_IO;
4. ...

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• 打开输出avio_open的时候, 第二参数不能是 NULL, 即使没有什么意义; ~~貌似自定义输出,不调用也可以 (实测) ~~
  

1. avio_open(&outAvFormatCtx->pb, "nothing",AVIO_FLAG_WRITE) ;
2. if (!outAvFormatCtx->pb ) {
3.     qDebug()<<"错误: format->pd is NULL";
4.     throw ("Error open ouput fail ");
5. }

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AVFormatContext 的pd 属性

AVFormatContext 有个 pd 属性指针, 读写数据都是通过它

1. // ============================
2. //      自定义 AVIO 输出
3. // ============================
5. struct AVIOCtxWrapper {
6.     JNIEnv *env;
7.     jobject wsServer;
8.     jmethodID broadcastFrame;
9. };
10. // 将 FFmpeg 封装输出的数据通过 WebSocket 发出
11. static int write_packet(void *opaque, uint8_t *buf, int buf_size) {
12.     auto *wrapper = (AVIOCtxWrapper *)opaque;
13.     if (!wrapper || !wrapper->env || !wrapper->wsServer) return 0;
15.     jbyteArray arr = wrapper->env->NewByteArray(buf_size);
16.     if (!arr) return 0;
17.     wrapper->env->SetByteArrayRegion(arr, 0, buf_size, reinterpret_cast<const jbyte*>(buf));
18.     wrapper->env->CallVoidMethod(wrapper->wsServer, wrapper->broadcastFrame, arr);
19.     wrapper->env->DeleteLocalRef(arr);
20.     return buf_size;
21. }
23. ................
25.          // --- 创建输出 fMP4 ---
26.         if (avformat_alloc_output_context2(&out_fmt, nullptr, "mp4", nullptr) < 0) {
27.                 LOGE("Failed to alloc output context");
28.                 cleanup();
29.                 return;
30.         }
31.         out_fmt->flags = AVFMT_FLAG_CUSTOM_IO;
32.        
33.   // 注意：write_packet 期望 wrapper 中持有一个有效的 JNIEnv 与 wsServer/global ref
34.     AVIOCtxWrapper wrapper;
35.     wrapper.env = env;
36.     wrapper.wsServer = ctx->wsServer;
37.     wrapper.broadcastFrame = broadcastFrame;
39.     avio = avio_alloc_context(
40.             avioBuffer, 8192, 1, &wrapper,
41.             nullptr,
42.             reinterpret_cast<int (*)(void *, const uint8_t *, int)>(write_packet),
43.             nullptr
44.     );
45.     if (!avio) {
46.         LOGE("avio_alloc_context failed");
47.         cleanup();
48.         return;
49.     }
50.     out_fmt->pb = avio;

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avio_alloc_context

1. /**
2.     * I/O context.
3.     *
4.     * - demuxing: either set by the user before avformat_open_input() (then
5.     *             the user must close it manually) or set by avformat_open_input().
6.     * - muxing: set by the user before avformat_write_header(). The caller must
7.     *           take care of closing / freeing the IO context.
8.     *
9.     * Do NOT set this field if AVFMT_NOFILE flag is set in
10.     * iformat/oformat.flags. In such a case, the (de)muxer will handle
11.     * I/O in some other way and this field will be NULL.
12.     */
13. AVIOContext *pb;

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可参考官方API 关于 avformat_open_input的文档:

If you want to use custom IO, preallocate the format context and set its pb field.

1. /**
2. * Allocate and initialize an AVIOContext for buffered I/O. It must be later
3. * freed with avio_context_free().
4. *
5. * @param buffer Memory block for input/output operations via AVIOContext.
6. *        The buffer must be allocated with av_malloc() and friends.
7. *        It may be freed and replaced with a new buffer by libavformat.
8. *        AVIOContext.buffer holds the buffer currently in use,
9. *        which must be later freed with av_free(). (输入输出的'操作容器',必须使用av_malloc()和friends来分配,av_free()释放, AVIOContext.buffer属性保存当前正在使用的)
10. * @param buffer_size The buffer size is very important for performance.
11. *        For protocols with fixed blocksize it should be set to this blocksize.
12. *        For others a typical size is a cache page, e.g. 4kb.['操作容器' 的大小]
13. * @param write_flag Set to 1 if the buffer should be writable, 0 otherwise.(如果 '操作容器' 可以写设置为1, 否则设置为0] 简而言之是否可写 /注意是个小坑)
14. * @param opaque An opaque pointer to user-specific data.[用户数据指针, 回调用]
15. * @param read_packet  A function for refilling the buffer, may be NULL.
16. *                     For stream protocols, must never return 0 but rather
17. *                     a proper AVERROR code. [读的 回调函数指针]
18. * @param write_packet A function for writing the buffer contents, may be NULL.
19. *        The function may not change the input buffers content.[写的 回调函数指针]
20. * @param seek A function for seeking to specified byte position, may be NULL.
21. *
22. * @return Allocated AVIOContext or NULL on failure.
23. */
24. AVIOContext *avio_alloc_context(
25.                   unsigned char *buffer,
26.                   int buffer_size,
27.                   int write_flag,
28.                   void *opaque,
29.                   int (*read_packet)(void *opaque, uint8_t *buf, int buf_size),
30.                   int (*write_packet)(void *opaque, uint8_t *buf, int buf_size),
31.                   int64_t (*seek)(void *opaque, int64_t offset, int whence));

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雷神的博客 - https://blog.csdn.net/leixiaohua1020/article/details/39759163

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