DVSDK码率控制的理解
1.动态参数和静态参数：
创建编码器的时候，有params和dynParams两种参数，顾名思义，Venc根据params创建，运行过程中又可以对dynParams改变配置
Venc1_Handle Venc1_create(Engine_Handle hEngine, Char *codecName,
VIDENC1_Params *params,VIDENC1_DynamicParams *dynParams)
| typedef struct IVIDENC1_Params { XDAS_Int32 size; /**< @sizeField */ XDAS_Int32 encodingPreset; /**< Encoding preset. */ XDAS_Int32 rateControlPreset;/**< @copydoc IVIDEO_RateControlPreset * * @sa IVIDEO_RateControlPreset */ XDAS_Int32 maxHeight; /**< Maximum height. */ XDAS_Int32 maxWidth; /**< Maximum width. */ XDAS_Int32 maxFrameRate; /**< Maximum frame rate in fps * 1000. * For example, if max frame rate is 30 * frames per second, set this field * to 30000. */ XDAS_Int32 maxBitRate; /**< Maximum bit rate, bits per second. */ XDAS_Int32 dataEndianness; /**< Endianness of output data. * * @sa XDM_DataFormat */ XDAS_Int32 maxInterFrameInterval;/**< I to P frame distance. e.g. = 1 if * no B frames, 2 to insert one B frame. * * @remarks This is used for setting the * maximum number of B frames * between two refererence frames. */ XDAS_Int32 inputChromaFormat;/**< Chroma format for the input buffer. * * @sa XDM_ChromaFormat */ XDAS_Int32 inputContentType;/**< Video content type of the buffer being * encoded. * * @sa IVIDEO_ContentType */ XDAS_Int32 reconChromaFormat;/**< Chroma formats for the reconstruction * buffers. * * @remarks The application should set * this to #XDM_CHROMA_NA * if reconstruction * buffers are not * required. * * @sa XDM_ChromaFormat */ } IVIDENC1_Params; |
typedef struct IVIDENC1_DynamicParams { XDAS_Int32 size; /**< @sizeField */ XDAS_Int32 inputHeight; /**< Input frame height. */ XDAS_Int32 inputWidth; /**< Input frame width. */ XDAS_Int32 refFrameRate; /**< Reference, or input, frame rate in * fps * 1000. * * @remarks For example, if ref frame * rate is 30 frames per second, * this field will be 30000. */ XDAS_Int32 targetFrameRate; /**< Target frame rate in * fps * 1000. * * @remarks For example, if target frame * rate is 30 frames per second, * this field will be 30000. */ XDAS_Int32 targetBitRate; /**< Target bit rate in bits per second. */ XDAS_Int32 intraFrameInterval;/**< The number of frames between two I * frames. For example, 30. * * @remarks For example, this field will be: * - 0 - Only first frame to be intra * coded. e.g. IPPPPPP... * - 1 - No inter frames (all intra * frames). * - 2 - Consecutive IPIPIP... sequence (if * no B frames). * - 3 - IPPIPP... or IPBIPBI... and so on. */ XDAS_Int32 generateHeader; /**< @copydoc XDM_EncMode * * @sa XDM_EncMode */ XDAS_Int32 captureWidth; /**< DEFAULT(0): use imagewidth as * pitch else use given capture * width for pitch provided it * is greater than image width. */ XDAS_Int32 forceFrame; /**< Force the current (immediate) frame to be * encoded as a specific frame type. * * @remarks For example, this field will be: * - IVIDEO_NA_FRAME - No forcing of any * specific frame type for the frame. * - IVIDEO_I_FRAME - Force the frame to be * encoded as I frame. * - IVIDEO_IDR_FRAME - Force the frame to * be encoded as an IDR frame (specific * to H.264 codecs). * - IVIDEO_P_FRAME - Force the frame to be * encoded as a P frame. * - IVIDEO_B_FRAME - Force the frame to be * encoded as a B frame. * * @sa IVIDEO_FrameType. */ XDAS_Int32 interFrameInterval;/**< Number of B frames between two reference * frames; that is, the number of B frames * between two P frames or I/P frames. * DEFAULT(0). * * @remarks For example, this field will be: * - 0 - to use maxInterFrameInterval. * - 1 - 0 B frames between two reference * frames. * - 2 - 1 B frame between two reference * frames. * - 3 - 2 B frames between two reference * frames. * - and so on... * * @sa IVIDENC1_Params.maxInterFrameInterval. */ XDAS_Int32 mbDataFlag; /**< Flag to indicate that the algorithm should * use MB data supplied in additional buffer * within inBufs. */ } IVIDENC1_DynamicParams; |
2.重要参数
若要进行码率和帧率控制，首先静态参数中，rateControlPreset是非常重要的一个参数，可选项有以下五种，其中CBR和VBR是我们要进行选择的，若不需要对码率帧率控制可直接选择NONE。
CBR编码时，在配置为较低比特率的时候，帧率也会随之下降，若采用VBR编码，可以始终保持较高的帧率，因为CBR是很定比特率编码，而VBR是根据图片复杂度优化。较少的变化采用较少的bit，复杂的地方采用较多的bit。因此码率较高的时候，CBR速度快，码率低的时候VBR较能改变图片质量。
IVIDEO_LOW_DELAY = 1, /**< CBR rate control for video conferencing. */
IVIDEO_STORAGE = 2, /**< VBR rate control for local storage (DVD)
* recording.
*/
IVIDEO_TWOPASS = 3, /**< Two pass rate control for non real time
* applications.
*/
IVIDEO_NONE = 4, /**< No configurable video rate control
* mechanism.
*/
IVIDEO_USER_DEFINED = 5,/**< User defined configuration using extended
* parameters.
在动态参数中，有两个值是同一个意思，可能是为了兼容性考虑，targetFrameRate是DM6467要配置的，refFrameRate虽然可以置之不理，但是当两个值设置为一致时，配置才不会报错，
XDAS_Int32 refFrameRate; /**< Reference, or input, frame rate in
* fps * 1000.
*
* @remarks For example, if ref frame
* rate is 30 frames per second,
* this field will be 30000.
*/
XDAS_Int32 targetFrameRate; /**< Target frame rate in
* fps * 1000.
*
* @remarks For example, if target frame
* rate is 30 frames per second,
* this field will be 30000.
*/