106 строки
4.5 KiB
Plaintext
106 строки
4.5 KiB
Plaintext
@TEMPLATE encoder_tmpl.c
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Simple Encoder
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==============
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ INTRODUCTION
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This is an example of a simple encoder loop. It takes an input file in
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YV12 format, passes it through the encoder, and writes the compressed
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frames to disk in IVF format. Other decoder examples build upon this
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one.
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The details of the IVF format have been elided from this example for
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simplicity of presentation, as IVF files will not generally be used by
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your application. In general, an IVF file consists of a file header,
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followed by a variable number of frames. Each frame consists of a frame
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header followed by a variable length payload. The length of the payload
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is specified in the first four bytes of the frame header. The payload is
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the raw compressed data.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ INTRODUCTION
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Standard Includes
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-----------------
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For encoders, you only have to include `vpx_encoder.h` and then any
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header files for the specific codecs you use. In this case, we're using
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vp8. The `VPX_CODEC_DISABLE_COMPAT` macro can be defined to ensure
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strict compliance with the latest SDK by disabling some backwards
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compatibility features. Defining this macro is encouraged.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ENC_INCLUDES
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@DEFAULT
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ENC_INCLUDES
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Getting The Default Configuration
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---------------------------------
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Encoders have the notion of "usage profiles." For example, an encoder
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may want to publish default configurations for both a video
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conferencing appliction and a best quality offline encoder. These
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obviously have very different default settings. Consult the
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documentation for your codec to see if it provides any default
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configurations. All codecs provide a default configuration, number 0,
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which is valid for material in the vacinity of QCIF/QVGA.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ENC_DEF_CFG
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@DEFAULT
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ENC_DEF_CFG
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Updating The Configuration
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---------------------------------
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Almost all applications will want to update the default configuration
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with settings specific to their usage. Here we set the width and height
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of the video file to that specified on the command line. We also scale
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the default bitrate based on the ratio between the default resolution
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and the resolution specified on the command line.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ENC_SET_CFG
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@DEFAULT
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ENC_SET_CFG
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Initializing The Codec
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----------------------
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The encoder is initialized by the following code.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ENC_INIT
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@DEFAULT
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ENC_INIT
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Encoding A Frame
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----------------
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The frame is read as a continuous block (size width * height * 3 / 2)
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from the input file. If a frame was read (the input file has not hit
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EOF) then the frame is passed to the encoder. Otherwise, a NULL
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is passed, indicating the End-Of-Stream condition to the encoder. The
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`frame_cnt` is reused as the presentation time stamp (PTS) and each
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frame is shown for one frame-time in duration. The flags parameter is
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unused in this example. The deadline is set to VPX_DL_REALTIME to
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make the example run as quickly as possible.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ENCODE_FRAME
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@DEFAULT
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ENCODE_FRAME
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Processing The Encoded Data
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---------------------------
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Each packet of type `VPX_CODEC_CX_FRAME_PKT` contains the encoded data
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for this frame. We write a IVF frame header, followed by the raw data.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PROCESS_FRAME
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@DEFAULT
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PROCESS_FRAME
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Cleanup
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-------
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The `vpx_codec_destroy` call frees any memory allocated by the codec.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ DESTROY
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@DEFAULT
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ DESTROY
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Error Handling
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--------------
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This example does not special case any error return codes. If there was
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an error, a descriptive message is printed and the program exits. With
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few exeptions, vpx_codec functions return an enumerated error status,
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with the value `0` indicating success.
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ DIE_CODEC
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@DEFAULT
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ DIE_CODEC
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