c++ - 源阅读器和自定义不可搜索的字节流

Question

我正在实现自定义 IMFByteStream 以通过网络流式传输视频，但问题是我无法将其对象传递给源解析器以创建媒体源，因为 CreateObjectFromByteStream 返回错误:

0xc00d36ee : The provided bytestream was expected to be seekable and it is not.

当然，我的自定义字节流是不可搜索的，因为无法通过网络进行搜索。所以问题是如何使用不可搜索的字节流创建媒体源？我的最终目标是创建一个 IMFSourceReader 对象。源内容类型为ASF。

Answer 1

我已经实现了两个 IMFByteStream 接口(interface)，一个称为 MediaByteStream，用于非存储内存流，另一个称为 StoreByteStream(是的，我知道)，用于内存存储。

将下面的代码放在您的 IMFByteStream 实现中将消除您的可搜索错误并且不会影响您的流式传输能力。

        /// <summary>
        /// Retrieves the characteristics of the byte stream.
        /// </summary>
        /// <param name="pdwCapabilities">Receives a bitwise OR of zero or more flags. The following flags are defined. [out]</param>
        /// <returns>The result of the operation.</returns>
        HRESULT MediaByteStream::GetCapabilities(
            DWORD *pdwCapabilities)
        {
            HRESULT hr = S_OK;

            // Stream can read, can write, can seek.
            *pdwCapabilities = MFBYTESTREAM_IS_READABLE | MFBYTESTREAM_IS_WRITABLE | MFBYTESTREAM_IS_SEEKABLE;

            // Return the result.
            return hr;
        }

如果您希望实现 IMFByteStream 接口(interface)的 Seek 方法，您可以这样做，但在您的情况下(网络流)，您可以只返回搜索位置。

        /// <summary>
        /// Moves the current position in the stream by a specified offset.
        /// </summary>
        /// <param name="SeekOrigin">Specifies the origin of the seek as a member of the MFBYTESTREAM_SEEK_ORIGIN enumeration. The offset is calculated relative to this position. [in]</param>
        /// <param name="qwSeekOffset">Specifies the new position, as a byte offset from the seek origin. [in]</param>
        /// <param name="dwSeekFlags">Specifies zero or more flags. The following flags are defined. [in]</param>
        /// <param name="pqwCurrentPosition">Receives the new position after the seek. [out]</param>
        /// <returns>The result of the operation.</returns>
        HRESULT MediaByteStream::Seek(
            MFBYTESTREAM_SEEK_ORIGIN SeekOrigin,
            LONGLONG                 qwSeekOffset,
            DWORD                    dwSeekFlags,
            QWORD                    *pqwCurrentPosition)
        {
            HRESULT hr = S_OK;
            _seekRequest = true;

            // Select the seek origin.
            switch (SeekOrigin)
            {
            case MFBYTESTREAM_SEEK_ORIGIN::msoCurrent:
                // If the buffer is less or same.
                if ((qwSeekOffset + _position) < size)
                    _position += qwSeekOffset;
                else
                    _position = size;

                break;

            case MFBYTESTREAM_SEEK_ORIGIN::msoBegin:
            default:
                // If the buffer is less or same.
                if (qwSeekOffset < size)
                    _position = qwSeekOffset;
                else
                    _position = size;

                break;
            }

            // Get the current position in the stream.
            *pqwCurrentPosition = _position;

            // Return the result.
            return hr;
        }