diff --git a/aegisub/audio_provider_lavc.cpp b/aegisub/audio_provider_lavc.cpp index 4f1feba43..65cb4ac29 100644 --- a/aegisub/audio_provider_lavc.cpp +++ b/aegisub/audio_provider_lavc.cpp @@ -105,20 +105,23 @@ LAVCAudioProvider::LAVCAudioProvider(Aegisub::String _filename) if (avcodec_open(codecContext, codec) < 0) throw _T("Failed to open audio decoder"); - /* aegisub currently supports mono only, so always resample */ - sample_rate = Options.AsInt(_T("Audio Sample Rate")); if (!sample_rate) sample_rate = codecContext->sample_rate; channels = 1; - bytes_per_sample = 2; + /* FIXME: this entire provider always assumes 16-bit audio. Currently that isn't a problem since + ffmpeg always converts everything to 16-bit, but in the future it might become one. */ + bytes_per_sample = 2; - rsct = audio_resample_init(1, codecContext->channels, sample_rate, codecContext->sample_rate); - if (!rsct) - throw _T("Failed to initialize resampling"); + /* aegisub currently supports mono only, so always resample unless it's mono with the desired samplerate */ + if ((sample_rate != codecContext->sample_rate) || (codecContext->channels > 1)) { + rsct = audio_resample_init(1, codecContext->channels, sample_rate, codecContext->sample_rate); + if (!rsct) + throw _T("Failed to initialize resampling"); - resample_ratio = (float)sample_rate / (float)codecContext->sample_rate; + resample_ratio = (float)sample_rate / (float)codecContext->sample_rate; + } double length = (double)stream->duration * av_q2d(stream->time_base); num_samples = (int64_t)(length * sample_rate); @@ -154,42 +157,49 @@ void LAVCAudioProvider::Destroy() void LAVCAudioProvider::GetAudio(void *buf, int64_t start, int64_t count) { int16_t *_buf = (int16_t *)buf; - int64_t _count = num_samples - start; - if (count < _count) - _count = count; - if (_count < 0) - _count = 0; + int64_t samples_to_decode = num_samples - start; /* samples left to the end of the stream */ + if (count < samples_to_decode) /* haven't reached the end yet, so just decode the requested number of samples */ + samples_to_decode = count; + if (samples_to_decode < 0) /* requested beyond the end of the stream */ + samples_to_decode = 0; - memset(_buf + _count, 0, (count - _count) << 1); + /* if we got asked for more samples than there are left in the stream, add zeros to the decoding buffer until + we have enough to fill the request */ + memset(_buf + samples_to_decode, 0, (count - samples_to_decode) * 2); AVPacket packet; - while (_count > 0 && av_read_frame(lavcfile->fctx, &packet) >= 0) { + while (samples_to_decode > 0 && av_read_frame(lavcfile->fctx, &packet) >= 0) { while (packet.stream_index == audStream) { - int bytesout = AVCODEC_MAX_AUDIO_FRAME_SIZE; /* see constructor, it malloc()'s buffer to this */ - int samples; - /* returns negative if error, 0 if no frame decoded, number of bytes used on success */ - if (avcodec_decode_audio2(codecContext, buffer, &bytesout, packet.data, packet.size) <= 0) + int temp_output_buffer_size = AVCODEC_MAX_AUDIO_FRAME_SIZE; /* see constructor, it malloc()'s buffer to this */ + int decoded_samples; + + if (avcodec_decode_audio2(codecContext, buffer, &temp_output_buffer_size, packet.data, packet.size) <= 0) throw _T("Failed to decode audio"); - if (bytesout == 0) /* sanity checking */ + if (temp_output_buffer_size == 0) /* gets changed to number of bytes actually output, so this is sanity checking */ break; - samples = bytesout >> 1; + decoded_samples = temp_output_buffer_size / 2; + /* do we need to resample? */ if (rsct) { - if ((int64_t)(samples * resample_ratio / codecContext->channels) > _count) - samples = (int64_t)(_count / resample_ratio * codecContext->channels); - samples = audio_resample(rsct, _buf, buffer, samples / codecContext->channels); + if ((int64_t)(decoded_samples * resample_ratio / codecContext->channels) > samples_to_decode) + decoded_samples = (int64_t)(samples_to_decode / resample_ratio * codecContext->channels); + decoded_samples = audio_resample(rsct, _buf, buffer, decoded_samples / codecContext->channels); - assert(samples <= _count); + /* make sure we somehow didn't end up with more samples than we wanted */ + assert(decoded_samples <= samples_to_decode); } else { - /* currently dead code, rsct != NULL because we're resampling for mono */ - if (samples > _count) - samples = _count; - memcpy(_buf, buffer, samples << 1); + /* no resampling needed, just copy to the buffer */ + /* if (decoded_samples > samples_to_decode) + decoded_samples = samples_to_decode; */ + /* I do not understand the point of the above, changed to a more reasonable assertation instead -Fluff */ + assert(decoded_samples <= samples_to_decode); + + memcpy(_buf, buffer, temp_output_buffer_size); } - _buf += samples; - _count -= samples; - break; + _buf += decoded_samples; + samples_to_decode -= decoded_samples; + /* break; */ /* why did this loop need to be broken manually? */ } av_free_packet(&packet);