ffmpeg重采样中swr_convert和swr_get_out_samples的用法
在做mux的时候关于重采样可以用fifo,或者audiofifo做缓存处理,当做demux的时候关于重采样就可以用到上面的swr_convert和swr_get_out_samples做配合处理。先看下这两个函数的注释:
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- /** Convert audio.
- *
- * in and in_count can be set to 0 to flush the last few samples out at the
- * end.
- *
- * If more input is provided than output space, then the input will be buffered.
- * You can avoid this buffering by using swr_get_out_samples() to retrieve an
- * upper bound on the required number of output samples for the given number of
- * input samples. Conversion will run directly without copying whenever possible.
- *
- * @param s allocated Swr context, with parameters set
- * @param out output buffers, only the first one need be set in case of packed audio
- * @param out_count amount of space available for output in samples per channel
- * @param in input buffers, only the first one need to be set in case of packed audio
- * @param in_count number of input samples available in one channel
- *
- * @return number of samples output per channel, negative value on error
- */
- int swr_convert(struct SwrContext *s, uint8_t **out, int out_count,
- const uint8_t **in , int in_count);
[cpp] view plain copy
- /**
- * Find an upper bound on the number of samples that the next swr_convert
- * call will output, if called with in_samples of input samples. This
- * depends on the internal state, and anything changing the internal state
- * (like further swr_convert() calls) will may change the number of samples
- * swr_get_out_samples() returns for the same number of input samples.
- *
- * @param in_samples number of input samples.
- * @note any call to swr_inject_silence(), swr_convert(), swr_next_pts()
- * or swr_set_compensation() invalidates this limit
- * @note it is recommended to pass the correct available buffer size
- * to all functions like swr_convert() even if swr_get_out_samples()
- * indicates that less would be used.
- * @returns an upper bound on the number of samples that the next swr_convert
- * will output or a negative value to indicate an error
- */
- int swr_get_out_samples(struct SwrContext *s, int in_samples);
就说如果传入的nb_samles大于了传出的nb_samplse则SwrContext中会有缓存,会导致内存一直暴涨,解决方法,可以看如下代码:
没有缓存的重采样这么处理:
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- ret = swr_convert(swrcontext, pOutputFrame->data,pOutputFrame->nb_samples,
- (const uint8_t**)pInputFrame->data,pInputFrame->nb_samples);
有缓存的代码这么处理:
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- //如果还有缓存在swrcontext中,第二个参数要填写0才能获取到,缓存数据
- int fifo_size = swr_get_out_samples(swrcontext,0);
- if ( fifo_size >= pOutputFrame->nb_samples)
- {
- ret = swr_convert(swrcontext, pOutputFrame->data,pOutputFrame->nb_samples,
- NULL,0);
- }
即如果有缓存则先判断是否有缓存在里面,如果有则传入数据为空取出缓存。