1、从解码数组获取到解码后的数据
static int audio_decode_frame(VideoState *is)
{
int data_size, resampled_data_size;
av_unused double audio_clock0;
int wanted_nb_samples;
Frame *af;
if (is->paused)
return -1;
//音频数组队列获取数据
do {
#if defined(_WIN32)
while (frame_queue_nb_remaining(&is->sampq) == 0) {
if ((av_gettime_relative() - audio_callback_time) > 1000000LL * is->audio_hw_buf_size / is->audio_tgt.bytes_per_sec / 2)
return -1;
av_usleep (1000);
}
#endif
if (!(af = frame_queue_peek_readable(&is->sampq)))
return -1;
frame_queue_next(&is->sampq);
} while (af->serial != is->audioq.serial);
// 获取音频数据
data_size = av_samples_get_buffer_size(NULL, af->frame->ch_layout.nb_channels, af->frame->nb_samples, af->frame->format, 1);
// 同步视频的转换
wanted_nb_samples = synchronize_audio(is, af->frame->nb_samples);
// 格式是否与SDL输出格式一样
if (af->frame->format != is->audio_src.fmt ||
av_channel_layout_compare(&af->frame->ch_layout, &is->audio_src.ch_layout) ||
af->frame->sample_rate != is->audio_src.freq ||
(wanted_nb_samples != af->frame->nb_samples && !is->swr_ctx)) {
swr_free(&is->swr_ctx);
// 重采样上下文
swr_alloc_set_opts2(&is->swr_ctx,
&is->audio_tgt.ch_layout, is->audio_tgt.fmt, is->audio_tgt.freq,
&af->frame->ch_layout, af->frame->format, af->frame->sample_rate,
0, NULL);
if (!is->swr_ctx || swr_init(is->swr_ctx) < 0) {
av_log(NULL, AV_LOG_ERROR,
"Cannot create sample rate converter for conversion of %d Hz %s %d channels to %d Hz %s %d channels!\n",
af->frame->sample_rate, av_get_sample_fmt_name(af->frame->format), af->frame->ch_layout.nb_channels,
is->audio_tgt.freq, av_get_sample_fmt_name(is->audio_tgt.fmt), is->audio_tgt.ch_layout.nb_channels);
swr_free(&is->swr_ctx);
return -1;
}
if (av_channel_layout_copy(&is->audio_src.ch_layout, &af->frame->ch_layout) < 0)
return -1;
is->audio_src.freq = af->frame->sample_rate;
is->audio_src.fmt = af->frame->format;
}
if (is->swr_ctx) {// 格式不同需要转换
//分配空间
const uint8_t **in = (const uint8_t **)af->frame->extended_data;
uint8_t **out = &is->audio_buf1;
int out_count = (int64_t)wanted_nb_samples * is->audio_tgt.freq / af->frame->sample_rate + 256;
int out_size = av_samples_get_buffer_size(NULL, is->audio_tgt.ch_layout.nb_channels, out_count, is->audio_tgt.fmt, 0);
int len2;
if (out_size < 0) {
av_log(NULL, AV_LOG_ERROR, "av_samples_get_buffer_size() failed\n");
return -1;
}
if (wanted_nb_samples != af->frame->nb_samples) {
if (swr_set_compensation(is->swr_ctx, (wanted_nb_samples - af->frame->nb_samples) * is->audio_tgt.freq / af->frame->sample_rate,
wanted_nb_samples * is->audio_tgt.freq / af->frame->sample_rate) < 0) {
av_log(NULL, AV_LOG_ERROR, "swr_set_compensation() failed\n");
return -1;
}
}
av_fast_malloc(&is->audio_buf1, &is->audio_buf1_size, out_size);
if (!is->audio_buf1)
return AVERROR(ENOMEM);
// 转换
len2 = swr_convert(is->swr_ctx, out, out_count, in, af->frame->nb_samples);
if (len2 < 0) {
av_log(NULL, AV_LOG_ERROR, "swr_convert() failed\n");
return -1;
}
if (len2 == out_count) {
av_log(NULL, AV_LOG_WARNING, "audio buffer is probably too small\n");
if (swr_init(is->swr_ctx) < 0)
swr_free(&is->swr_ctx);
}
is->audio_buf = is->audio_buf1;
resampled_data_size = len2 * is->audio_tgt.ch_layout.nb_channels * av_get_bytes_per_sample(is->audio_tgt.fmt);
} else {// 格式相同直接传递
is->audio_buf = af->frame->data[0];
resampled_data_size = data_size;
}
audio_clock0 = is->audio_clock;
// af->pts不是无效值时，更新VideoState音频的PTS，让video同步用
if (!isnan(af->pts))
is->audio_clock = af->pts + (double) af->frame->nb_samples / af->frame->sample_rate;
else
is->audio_clock = NAN;
is->audio_clock_serial = af->serial;
#ifdef DEBUG
{
static double last_clock;
printf("audio: delay=%0.3f clock=%0.3f clock0=%0.3f\n", is->audio_clock - last_clock, is->audio_clock, audio_clock0);
last_clock = is->audio_clock;
}
#endif
return resampled_data_size;
}
2、放到sdl缓存播放回调函数
static void sdl_audio_callback(void *opaque, Uint8 *stream, int len)
{
VideoState *is = opaque;
int audio_size, len1;
audio_callback_time = av_gettime_relative();
// 缓存区需要数据填充
while (len > 0) {
// audio_buf的播放数据已经消耗完了，需要重新获取数据
if (is->audio_buf_index >= is->audio_buf_size) {
audio_size = audio_decode_frame(is);
if (audio_size < 0) {
/* if error, just output silence */
is->audio_buf = NULL;
is->audio_buf_size = SDL_AUDIO_MIN_BUFFER_SIZE / is->audio_tgt.frame_size * is->audio_tgt.frame_size;
} else {
if (is->show_mode != SHOW_MODE_VIDEO)
update_sample_display(is, (int16_t *)is->audio_buf, audio_size);
is->audio_buf_size = audio_size;
}
is->audio_buf_index = 0;
}
// 可播放数据长度
len1 = is->audio_buf_size - is->audio_buf_index;
if (len1 > len)
len1 = len;
//拷贝数据
if (!is->muted && is->audio_buf && is->audio_volume == SDL_MIX_MAXVOLUME) //音量最大时直接拷贝
memcpy(stream, (uint8_t *)is->audio_buf + is->audio_buf_index, len1);
else {
//清空stream
memset(stream, 0, len1);
//不是静音时混音处理
if (!is->muted && is->audio_buf)
SDL_MixAudioFormat(stream, (uint8_t *)is->audio_buf + is->audio_buf_index, AUDIO_S16SYS, len1, is->audio_volume);
}
// 移动位置
len -= len1;
stream += len1;
is->audio_buf_index += len1;
}
// 音频播放数据
is->audio_write_buf_size = is->audio_buf_size - is->audio_buf_index;
// 当audio时钟无效时，通过计算采样点获取，我们假设 SDL 使用的音频驱动程序有两个周期。
if (!isnan(is->audio_clock)) {
set_clock_at(&is->audclk, is->audio_clock - (double)(2 * is->audio_hw_buf_size + is->audio_write_buf_size) / is->audio_tgt.bytes_per_sec, is->audio_clock_serial, audio_callback_time / 1000000.0);
sync_clock_to_slave(&is->extclk, &is->audclk);
}
}
3、sdl音频播放初始化，在stream_component_open打开音频时打开
static int audio_open(void *opaque, AVChannelLayout *wanted_channel_layout, int wanted_sample_rate, struct AudioParams *audio_hw_params)
{
SDL_AudioSpec wanted_spec, spec;
const char *env;
static const int next_nb_channels[] = {0, 0, 1, 6, 2, 6, 4, 6};
static const int next_sample_rates[] = {0, 44100, 48000, 96000, 192000};
int next_sample_rate_idx = FF_ARRAY_ELEMS(next_sample_rates) - 1;
int wanted_nb_channels = wanted_channel_layout->nb_channels;
// 获取SDL通道数
env = SDL_getenv("SDL_AUDIO_CHANNELS");
if (env) {
wanted_nb_channels = atoi(env);
av_channel_layout_uninit(wanted_channel_layout);
av_channel_layout_default(wanted_channel_layout, wanted_nb_channels);
}
// 声道布局变声道数
if (wanted_channel_layout->order != AV_CHANNEL_ORDER_NATIVE) {
av_channel_layout_uninit(wanted_channel_layout);
av_channel_layout_default(wanted_channel_layout, wanted_nb_channels);
}
wanted_nb_channels = wanted_channel_layout->nb_channels;
// 初始化SDL播放参数
wanted_spec.channels = wanted_nb_channels;
wanted_spec.freq = wanted_sample_rate;
if (wanted_spec.freq <= 0 || wanted_spec.channels <= 0) {
av_log(NULL, AV_LOG_ERROR, "Invalid sample rate or channel count!\n");
return -1;
}
while (next_sample_rate_idx && next_sample_rates[next_sample_rate_idx] >= wanted_spec.freq)
next_sample_rate_idx--;
wanted_spec.format = AUDIO_S16SYS;
wanted_spec.silence = 0;
wanted_spec.samples = FFMAX(SDL_AUDIO_MIN_BUFFER_SIZE, 2 << av_log2(wanted_spec.freq / SDL_AUDIO_MAX_CALLBACKS_PER_SEC));
wanted_spec.callback = sdl_audio_callback;
wanted_spec.userdata = opaque;
// 打开SDL音频播放器
while (!(audio_dev = SDL_OpenAudioDevice(NULL, 0, &wanted_spec, &spec, SDL_AUDIO_ALLOW_FREQUENCY_CHANGE | SDL_AUDIO_ALLOW_CHANNELS_CHANGE))) {
av_log(NULL, AV_LOG_WARNING, "SDL_OpenAudio (%d channels, %d Hz): %s\n", wanted_spec.channels, wanted_spec.freq, SDL_GetError());
wanted_spec.channels = next_nb_channels[FFMIN(7, wanted_spec.channels)];
if (!wanted_spec.channels) {
wanted_spec.freq = next_sample_rates[next_sample_rate_idx--];
wanted_spec.channels = wanted_nb_channels;
if (!wanted_spec.freq) {
av_log(NULL, AV_LOG_ERROR, "No more combinations to try, audio open failed\n");
return -1;
}
}
av_channel_layout_default(wanted_channel_layout, wanted_spec.channels);
}
// 检测打开的格式是否正确
if (spec.format != AUDIO_S16SYS) {
av_log(NULL, AV_LOG_ERROR, "SDL advised audio format %d is not supported!\n", spec.format);
return -1;
}
// 检测打开的通道数是否正确
if (spec.channels != wanted_spec.channels) {
av_channel_layout_uninit(wanted_channel_layout);
av_channel_layout_default(wanted_channel_layout, spec.channels);
if (wanted_channel_layout->order != AV_CHANNEL_ORDER_NATIVE) {
av_log(NULL, AV_LOG_ERROR, "SDL advised channel count %d is not supported!\n", spec.channels);
return -1;
}
}
// 返回播放的音频参数，播放时是否需要转换
audio_hw_params->fmt = AV_SAMPLE_FMT_S16;
audio_hw_params->freq = spec.freq;
if (av_channel_layout_copy(&audio_hw_params->ch_layout, wanted_channel_layout) < 0)
return -1;
audio_hw_params->frame_size = av_samples_get_buffer_size(NULL, audio_hw_params->ch_layout.nb_channels, 1, audio_hw_params->fmt, 1);
audio_hw_params->bytes_per_sec = av_samples_get_buffer_size(NULL, audio_hw_params->ch_layout.nb_channels, audio_hw_params->freq, audio_hw_params->fmt, 1);
if (audio_hw_params->bytes_per_sec <= 0 || audio_hw_params->frame_size <= 0) {
av_log(NULL, AV_LOG_ERROR, "av_samples_get_buffer_size failed\n");
return -1;
}
return spec.size;
}