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我有一个程序，应该解复用输入mpeg-ts，将mpeg2转码为h264，然后将音频与转码后的视频一起复用。当我用VLC打开产生的多路复用文件时，我既没有音频也没有视频。这是相关的代码。MUX与libav
我的主要工作人员环路如下：
void
*writer_thread(void *thread_ctx) {
struct transcoder_ctx_t *ctx = (struct transcoder_ctx_t *) thread_ctx;
AVStream *video_stream = NULL, *audio_stream = NULL;
AVFormatContext *output_context = init_output_context(ctx, &video_stream, &audio_stream);
struct mux_state_t mux_state = {0};
//from omxtx
mux_state.pts_offset = av_rescale_q(ctx->input_context->start_time, AV_TIME_BASE_Q, output_context->streams[ctx->video_stream_index]->time_base);
//write stream header if any
avformat_write_header(output_context, NULL);
//do not start doing anything until we get an encoded packet
pthread_mutex_lock(&ctx->pipeline.video_encode.is_running_mutex);
while (!ctx->pipeline.video_encode.is_running) {
pthread_cond_wait(&ctx->pipeline.video_encode.is_running_cv, &ctx->pipeline.video_encode.is_running_mutex);
}
while (!ctx->pipeline.video_encode.eos || !ctx->processed_audio_queue->queue_finished) {
//FIXME a memory barrier is required here so that we don't race
//on above variables
//fill a buffer with video data
OERR(OMX_FillThisBuffer(ctx->pipeline.video_encode.h, omx_get_next_output_buffer(&ctx->pipeline.video_encode)));
write_audio_frame(output_context, audio_stream, ctx); //write full audio frame
//FIXME no guarantee that we have a full frame per packet?
write_video_frame(output_context, video_stream, ctx, &mux_state); //write full video frame
//encoded_video_queue is being filled by the previous command
}
av_write_trailer(output_context);
//free all the resources
avcodec_close(video_stream->codec);
avcodec_close(audio_stream->codec);
/* Free the streams. */
for (int i = 0; i < output_context->nb_streams; i++) {
av_freep(&output_context->streams[i]->codec);
av_freep(&output_context->streams[i]);
}
if (!(output_context->oformat->flags & AVFMT_NOFILE)) {
/* Close the output file. */
avio_close(output_context->pb);
}
/* free the stream */
av_free(output_context);
free(mux_state.pps);
free(mux_state.sps);
}
用于初始化libav输出上下文中的代码是这样的：
static
AVFormatContext *
init_output_context(const struct transcoder_ctx_t *ctx, AVStream **video_stream, AVStream **audio_stream) {
AVFormatContext *oc;
AVOutputFormat *fmt;
AVStream *input_stream, *output_stream;
AVCodec *c;
AVCodecContext *cc;
int audio_copied = 0; //copy just 1 stream
fmt = av_guess_format("mpegts", NULL, NULL);
if (!fmt) {
fprintf(stderr, "[DEBUG] Error guessing format, dying\n");
exit(199);
}
oc = avformat_alloc_context();
if (!oc) {
fprintf(stderr, "[DEBUG] Error allocating context, dying\n");
exit(200);
}
oc->oformat = fmt;
snprintf(oc->filename, sizeof(oc->filename), "%s", ctx->output_filename);
oc->debug = 1;
oc->start_time_realtime = ctx->input_context->start_time;
oc->start_time = ctx->input_context->start_time;
oc->duration = 0;
oc->bit_rate = 0;
for (int i = 0; i < ctx->input_context->nb_streams; i++) {
input_stream = ctx->input_context->streams[i];
output_stream = NULL;
if (input_stream->index == ctx->video_stream_index) {
//copy stuff from input video index
c = avcodec_find_encoder(CODEC_ID_H264);
output_stream = avformat_new_stream(oc, c);
*video_stream = output_stream;
cc = output_stream->codec;
cc->width = input_stream->codec->width;
cc->height = input_stream->codec->height;
cc->codec_id = CODEC_ID_H264;
cc->codec_type = AVMEDIA_TYPE_VIDEO;
cc->bit_rate = ENCODED_BITRATE;
cc->time_base = input_stream->codec->time_base;
output_stream->avg_frame_rate = input_stream->avg_frame_rate;
output_stream->r_frame_rate = input_stream->r_frame_rate;
output_stream->start_time = AV_NOPTS_VALUE;
} else if ((input_stream->codec->codec_type == AVMEDIA_TYPE_AUDIO) && !audio_copied) {
/* i care only about audio */
c = avcodec_find_encoder(input_stream->codec->codec_id);
output_stream = avformat_new_stream(oc, c);
*audio_stream = output_stream;
avcodec_copy_context(output_stream->codec, input_stream->codec);
/* Apparently fixes a crash on .mkvs with attachments: */
av_dict_copy(&output_stream->metadata, input_stream->metadata, 0);
/* Reset the codec tag so as not to cause problems with output format */
output_stream->codec->codec_tag = 0;
audio_copied = 1;
}
}
for (int i = 0; i < oc->nb_streams; i++) {
if (oc->oformat->flags & AVFMT_GLOBALHEADER)
oc->streams[i]->codec->flags |= CODEC_FLAG_GLOBAL_HEADER;
if (oc->streams[i]->codec->sample_rate == 0)
oc->streams[i]->codec->sample_rate = 48000; /* ish */
}
if (!(fmt->flags & AVFMT_NOFILE)) {
fprintf(stderr, "[DEBUG] AVFMT_NOFILE set, allocating output container\n");
if (avio_open(&oc->pb, ctx->output_filename, AVIO_FLAG_WRITE) < 0) {
fprintf(stderr, "[DEBUG] error creating the output context\n");
exit(1);
}
}
return oc;
}
最后，这是用于编写音频代码：
static
void
write_audio_frame(AVFormatContext *oc, AVStream *st, struct transcoder_ctx_t *ctx) {
AVPacket pkt = {0}; // data and size must be 0;
struct packet_t *source_audio;
av_init_packet(&pkt);
if (!(source_audio = packet_queue_get_next_item_asynch(ctx->processed_audio_queue))) {
return;
}
pkt.stream_index = st->index;
pkt.size = source_audio->data_length;
pkt.data = source_audio->data;
pkt.pts = source_audio->PTS;
pkt.dts = source_audio->DTS;
pkt.duration = source_audio->duration;
pkt.destruct = avpacket_destruct;
/* Write the compressed frame to the media file. */
if (av_interleaved_write_frame(oc, &pkt) != 0) {
fprintf(stderr, "[DEBUG] Error while writing audio frame\n");
}
packet_queue_free_packet(source_audio, 0);
}
生成的mpeg4文件可以从这里获得：http://87.120.131.41/dl/mpeg4.h264
我已经中省略了write_video_frame代码，因为它是一个复杂得多，我可能会犯一些错误存在，因为我做的时基的对话等。然而声音我在做1：1拷贝。每个packet_t包都包含来自输入mpegts容器的av_read_frame的数据。在最糟糕的情况下，我希望我的音频工作，而不是我的视频。不过，我无法让其中的任何一个工作。看起来这些文档在做这类事情时相当模糊 - 我试过libav和ffmpeg irc频道都无济于事。任何有关我如何调试问题的信息将不胜感激。
您使用MPEGTS输出格式。我不认为这是正确的，尝试一个容器，如MP4或AVI –
AVI没有帮助，但与MP4我没有得到图片，但没有声音。我不明白的是为什么它会影响容器的性能？ – LordDoskias
我需要看到更多的程序。我可以提取音频（它是来自脏作业的剪辑）但是视频流有些问题。 – szatmary