Fix stutter in ffmpeg movie audio

Attempting to calculate the resampling delay for determining the number
of out samples was actually causing underruns. There is no harm in not
accounting for any resample delay because any samples not taken are
buffered for the next conversion.

CorsixTH/Src/th_movie.cpp

@@ -1004,7 +1004,6 @@ int THMovie::decodeAudioFrame(bool fFirst)
         }
     }
 
-#if LIBSWRESAMPLE_VERSION_INT < AV_VERSION_INT(0, 12, 100)
     //over-estimate output samples
     iOutSamples = (int)av_rescale_rnd(m_frame->nb_samples, m_iMixerFrequency, m_pAudioCodecContext->sample_rate, AV_ROUND_UP);
     iSampleSize = av_get_bytes_per_sample(AV_SAMPLE_FMT_S16) * iOutSamples * m_iMixerChannels;
@@ -1018,27 +1017,6 @@ int THMovie::decodeAudioFrame(bool fFirst)
         m_pbAudioBuffer = (uint8_t*)av_malloc(iSampleSize);
         m_iAudioBufferMaxSize = iSampleSize;
     }
-#else
-    //output samples = (input samples + delay) * output rate / input rate
-    iOutSamples = (int)av_rescale_rnd(
-        swr_get_delay(
-            m_pAudioResampleContext,
-            m_pAudioCodecContext->sample_rate) + m_frame->nb_samples,
-            m_iMixerFrequency,
-            m_pAudioCodecContext->sample_rate,
-            AV_ROUND_UP);
-    iSampleSize = av_samples_get_buffer_size(NULL, m_iMixerChannels, iOutSamples, AV_SAMPLE_FMT_S16, 0);
-
-    if(iSampleSize > m_iAudioBufferMaxSize)
-    {
-        if(m_iAudioBufferMaxSize > 0)
-        {
-            av_free(m_pbAudioBuffer);
-        }
-        av_samples_alloc(&m_pbAudioBuffer, NULL, m_iMixerChannels, iOutSamples, AV_SAMPLE_FMT_S16, 0);
-        m_iAudioBufferMaxSize = iSampleSize;
-    }
-#endif
 
 #ifdef CORSIX_TH_USE_FFMPEG
     swr_convert(m_pAudioResampleContext, &m_pbAudioBuffer, iOutSamples, (const uint8_t**)&m_frame->data[0], m_frame->nb_samples);