從記憶中讀書

libavformat 通常接受檔名並直接從檔案系統讀取媒體。如果要從記憶體中讀取（例如流），請執行以下操作：

// Define your buffer size
const int FILESTREAMBUFFERSZ = 8192;

// A IStream - you choose where it comes from
IStream* fileStreamData;

// Alloc a buffer for the stream
unsigned char* fileStreamBuffer = (unsigned char*)av_malloc(FILESTREAMBUFFERSZ);
if (fileStreamBuffer == nullptr){
    // out of memory
}

// Get a AVContext stream
AVIOContext* ioContext = avio_alloc_context(
    fileStreamBuffer,    // Buffer
    FILESTREAMBUFFERSZ,  // Buffer size
    0,                   // Buffer is only readable - set to 1 for read/write
    fileStreamData,      // User (your) specified data
    FileStreamRead,      // Function - Reading Packets (see example)
    0,                   // Function - Write Packets
    FileStreamSeek       // Function - Seek to position in stream (see example)
);
if(ioContext == nullptr){
    // out of memory
}

// Allocate a AVContext
AVFormatContext *formatContext = avformat_alloc_context();

// Set up the Format Context
formatContext->pb = ioContext;
formatContext->flags |= AVFMT_FLAG_CUSTOM_IO; // we set up our own IO

// Open "file" (open our custom IO)
// Empty string is where filename would go. Doesn't matter since we aren't reading a file
// NULL params are format and demuxer settings, respectively
if (avformat_open_input(&formatContext, "", nullptr, nullptr) < 0){
    // Error opening file
}

// Do something with the formatContext

// Free resources!
avformat_close_input(&formatContext);
av_free(ioContext);