* allocated with swr_alloc() or swr_alloc_set_opts(). It is opaque, so all parameters
* must be set with the @ref avoptions API.
*
+ * The first thing you will need to do in order to use lswr is to allocate
+ * SwrContext. This can be done with swr_alloc() or swr_alloc_set_opts(). If you
+ * are using the former, you must set options through the @ref avoptions API.
+ * The latter function provides the same feature, but it allows you to set some
+ * common options in the same statement.
+ *
* For example the following code will setup conversion from planar float sample
* format to interleaved signed 16-bit integer, downsampling from 48kHz to
* 44.1kHz and downmixing from 5.1 channels to stereo (using the default mixing
- * matrix):
+ * matrix). This is using the swr_alloc() function.
* @code
* SwrContext *swr = swr_alloc();
* av_opt_set_channel_layout(swr, "in_channel_layout", AV_CH_LAYOUT_5POINT1, 0);
* av_opt_set_sample_fmt(swr, "out_sample_fmt", AV_SAMPLE_FMT_S16, 0);
* @endcode
*
+ * The same job can be done using swr_alloc_set_opts() as well:
+ * @code
+ * SwrContext *swr = swr_alloc_set_opts(NULL, // we're allocating a new context
+ * AV_CH_LAYOUT_STEREO, // out_ch_layout
+ * AV_SAMPLE_FMT_S16, // out_sample_fmt
+ * 44100, // out_sample_rate
+ * AV_CH_LAYOUT_5POINT1, // in_ch_layout
+ * AV_SAMPLE_FMT_FLTP, // in_sample_fmt
+ * 48000, // in_sample_rate
+ * 0, // log_offset
+ * NULL); // log_ctx
+ * @endcode
+ *
* Once all values have been set, it must be initialized with swr_init(). If
* you need to change the conversion parameters, you can change the parameters
- * as described above, or by using swr_alloc_set_opts(), then call swr_init()
- * again.
+ * using @ref AVOptions, as described above in the first example; or by using
+ * swr_alloc_set_opts(), but with the first argument the allocated context.
+ * You must then call swr_init() again.
*
* The conversion itself is done by repeatedly calling swr_convert().
* Note that the samples may get buffered in swr if you provide insufficient
* At the end of conversion the resampling buffer can be flushed by calling
* swr_convert() with NULL in and 0 in_count.
*
+ * The samples used in the conversion process can be managed with the libavutil
+ * @ref lavu_sampmanip "samples manipulation" API, including av_samples_alloc()
+ * function used in the following example.
+ *
* The delay between input and output, can at any time be found by using
* swr_get_delay().
*
*
* When the conversion is finished, the conversion
* context and everything associated with it must be freed with swr_free().
+ * A swr_close() function is also available, but it exists mainly for
+ * compatibility with libavresample, and is not required to be called.
+ *
* There will be no memory leak if the data is not completely flushed before
* swr_free().
*/
#define SWR_CH_MAX 32 ///< Maximum number of channels
#endif
+/**
+ * @name Option constants
+ * These constants are used for the @ref avoptions interface for lswr.
+ * @{
+ *
+ */
+
#define SWR_FLAG_RESAMPLE 1 ///< Force resampling even if equal sample rate
//TODO use int resample ?
//long term TODO can we enable this dynamically?
+/** Dithering algorithms */
enum SwrDitherType {
SWR_DITHER_NONE = 0,
SWR_DITHER_RECTANGULAR,
SWR_FILTER_TYPE_KAISER, /**< Kaiser Windowed Sinc */
};
+/**
+ * @}
+ */
+
+/**
+ * The libswresample context. Unlike libavcodec and libavformat, this structure
+ * is opaque. This means that if you would like to set options, you must use
+ * the @ref avoptions API and cannot directly set values to members of the
+ * structure.
+ */
typedef struct SwrContext SwrContext;
/**
- * Get the AVClass for swrContext. It can be used in combination with
+ * Get the AVClass for SwrContext. It can be used in combination with
* AV_OPT_SEARCH_FAKE_OBJ for examining options.
*
* @see av_opt_find().
+ * @return the AVClass of SwrContext
*/
const AVClass *swr_get_class(void);
/**
+ * @name SwrContext constructor functions
+ * @{
+ */
+
+/**
* Allocate SwrContext.
*
* If you use this function you will need to set the parameters (manually or
/**
* Initialize context after user parameters have been set.
*
+ * @param[in,out] s Swr context to initialize
* @return AVERROR error code in case of failure.
*/
int swr_init(struct SwrContext *s);
/**
* Check whether an swr context has been initialized or not.
*
+ * @param[in] s Swr context to check
+ * @see swr_init()
* @return positive if it has been initialized, 0 if not initialized
*/
int swr_is_initialized(struct SwrContext *s);
* other hand, swr_alloc() can use swr_alloc_set_opts() to set the parameters
* on the allocated context.
*
- * @param s Swr context, can be NULL
+ * @param s existing Swr context if available, or NULL if not
* @param out_ch_layout output channel layout (AV_CH_LAYOUT_*)
* @param out_sample_fmt output sample format (AV_SAMPLE_FMT_*).
* @param out_sample_rate output sample rate (frequency in Hz)
int log_offset, void *log_ctx);
/**
+ * @}
+ *
+ * @name SwrContext destructor functions
+ * @{
+ */
+
+/**
* Free the given SwrContext and set the pointer to NULL.
+ *
+ * @param[in] s a pointer to a pointer to Swr context
*/
void swr_free(struct SwrContext **s);
/**
* Closes the context so that swr_is_initialized() returns 0.
*
- * the context can be brougt back to life by running swr_init(),
+ * The context can be brought back to life by running swr_init(),
* swr_init() can also be used without swr_close().
* This function is mainly provided for simplifying the usecase
- * where one tries to support libavresample and libswresample
+ * where one tries to support libavresample and libswresample.
+ *
+ * @param[in,out] s Swr context to be closed
*/
void swr_close(struct SwrContext *s);
/**
- * Convert audio.
+ * @}
+ *
+ * @name Core conversion functions
+ * @{
+ */
+
+/** Convert audio.
*
* in and in_count can be set to 0 to flush the last few samples out at the
* end.
* timestamps are in 1/(in_sample_rate * out_sample_rate) units.
*
* @note There are 2 slightly differently behaving modes.
- * First is when automatic timestamp compensation is not used, (min_compensation >= FLT_MAX)
+ * @li When automatic timestamp compensation is not used, (min_compensation >= FLT_MAX)
* in this case timestamps will be passed through with delays compensated
- * Second is when automatic timestamp compensation is used, (min_compensation < FLT_MAX)
- * in this case the output timestamps will match output sample numbers
- *
- * @param pts timestamp for the next input sample, INT64_MIN if unknown
+ * @li When automatic timestamp compensation is used, (min_compensation < FLT_MAX)
+ * in this case the output timestamps will match output sample numbers.
+ * See ffmpeg-resampler(1) for the two modes of compensation.
+ *
+ * @param s[in] initialized Swr context
+ * @param pts[in] timestamp for the next input sample, INT64_MIN if unknown
+ * @see swr_set_compensation(), swr_drop_output(), and swr_inject_silence() are
+ * function used internally for timestamp compensation.
* @return the output timestamp for the next output sample
*/
int64_t swr_next_pts(struct SwrContext *s, int64_t pts);
/**
- * Activate resampling compensation.
+ * @}
+ *
+ * @name Low-level option setting functions
+ * These functons provide a means to set low-level options that is not possible
+ * with the AVOption API.
+ * @{
+ */
+
+/**
+ * Activate resampling compensation ("soft" compensation). This function is
+ * internally called when needed in swr_next_pts().
+ *
+ * @param[in,out] s allocated Swr context. If it is not initialized,
+ * or SWR_FLAG_RESAMPLE is not set, swr_init() is
+ * called with the flag set.
+ * @param[in] sample_delta delta in PTS per sample
+ * @param[in] compensation_distance number of samples to compensate for
+ * @return >= 0 on success, AVERROR error codes if:
+ * @li @c s is NULL,
+ * @li @c compensation_distance is less than 0,
+ * @li @c compensation_distance is 0 but sample_delta is not,
+ * @li compensation unsupported by resampler, or
+ * @li swr_init() fails when called.
*/
int swr_set_compensation(struct SwrContext *s, int sample_delta, int compensation_distance);
/**
* Set a customized input channel mapping.
*
- * @param s allocated Swr context, not yet initialized
- * @param channel_map customized input channel mapping (array of channel
- * indexes, -1 for a muted channel)
- * @return AVERROR error code in case of failure.
+ * @param[in,out] s allocated Swr context, not yet initialized
+ * @param[in] channel_map customized input channel mapping (array of channel
+ * indexes, -1 for a muted channel)
+ * @return >= 0 on success, or AVERROR error code in case of failure.
*/
int swr_set_channel_mapping(struct SwrContext *s, const int *channel_map);
* @param matrix remix coefficients; matrix[i + stride * o] is
* the weight of input channel i in output channel o
* @param stride offset between lines of the matrix
- * @return AVERROR error code in case of failure.
+ * @return >= 0 on success, or AVERROR error code in case of failure.
*/
int swr_set_matrix(struct SwrContext *s, const double *matrix, int stride);
/**
+ * @}
+ *
+ * @name Sample handling functions
+ * @{
+ */
+
+/**
* Drops the specified number of output samples.
+ *
+ * This function, along with swr_inject_silence(), is called by swr_next_pts()
+ * if needed for "hard" compensation.
+ *
+ * @param s allocated Swr context
+ * @param count number of samples to be dropped
+ *
+ * @return >= 0 on success, or a negative AVERROR code on failure
*/
int swr_drop_output(struct SwrContext *s, int count);
/**
* Injects the specified number of silence samples.
+ *
+ * This function, along with swr_drop_output(), is called by swr_next_pts()
+ * if needed for "hard" compensation.
+ *
+ * @param s allocated Swr context
+ * @param count number of samples to be dropped
+ *
+ * @return >= 0 on success, or a negative AVERROR code on failure
*/
int swr_inject_silence(struct SwrContext *s, int count);
* for upsampling and the input sample rate.
*
* @param s swr context
- * @param base timebase in which the returned delay will be
- * if its set to 1 the returned delay is in seconds
- * if its set to 1000 the returned delay is in milli seconds
- * if its set to the input sample rate then the returned delay is in input samples
- * if its set to the output sample rate then the returned delay is in output samples
- * an exact rounding free delay can be found by using LCM(in_sample_rate, out_sample_rate)
- * @returns the delay in 1/base units.
+ * @param base timebase in which the returned delay will be:
+ * @li if it's set to 1 the returned delay is in seconds
+ * @li if it's set to 1000 the returned delay is in milliseconds
+ * @li if it's set to the input sample rate then the returned
+ * delay is in input samples
+ * @li if it's set to the output sample rate then the returned
+ * delay is in output samples
+ * @li if it's the least common multiple of in_sample_rate and
+ * out_sample_rate then an exact rounding-free delay will be
+ * returned
+ * @returns the delay in 1 / @c base units.
*/
int64_t swr_get_delay(struct SwrContext *s, int64_t base);
/**
- * Return the LIBSWRESAMPLE_VERSION_INT constant.
+ * @}
+ *
+ * @name Configuration accessors
+ * @{
+ */
+
+/**
+ * Return the @ref LIBSWRESAMPLE_VERSION_INT constant.
+ *
+ * This is useful to check if the build-time libswresample has the same version
+ * as the run-time one.
+ *
+ * @returns the unsigned int-typed version
*/
unsigned swresample_version(void);
/**
* Return the swr build-time configuration.
+ *
+ * @returns the build-time @c ./configure flags
*/
const char *swresample_configuration(void);
/**
* Return the swr license.
+ *
+ * @returns the license of libswresample, determined at build-time
*/
const char *swresample_license(void);
/**
* @}
+ * @}
*/
#endif /* SWRESAMPLE_SWRESAMPLE_H */
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