说明
一般使用av_find_stream_info函数探测码流格式，它的作用是为pFormatContext->streams填充上正确的音视频格式信息。可以通过av_dump_format函数将音视频数据格式通过av_log输出到指定的文件或者控制台,方便开发者了解输入的视音频格式，对于程序的调用，删除该函数的调用没有任何的影响
声明
/**
* Print detailed information about the input or output format, such as
* duration, bitrate, streams, container, programs, metadata, side data,
* codec and time base（打印输入或者输出格式的信息，例如视频总时长，波特率，流，容器，程序，元数据，边数据，编码器，时间戳）.
*
* @param ic the context to analyze（被分析的视音频上下文）
* @param index index of the stream to dump information about（需要解析的流索引号，例如0是视频流，1是音频流）
* @param url the URL to print, such as source or destination file（打印URL，例如源文件或者目的文件）
* @param is_output Select whether the specified context is an input(0) or output(1)（指定的视音频上下文是输入流（0）还是输出流（1））
*/
void av_dump_format(AVFormatContext *ic,
int index,
const char *url,
int is_output);调用代码
av_dump_format(pFormatContext, 0, "", 0);注意：最后一个参数如果是输入流取值0，如果是输出流取值1
日志输出
通过av_log_set_callback设置日志文件输出，输出的结果如下：
Input #0, h264, from '':
Duration: N/A, bitrate: N/A
Stream #0:0, 0, 1/1200000: Video: h264 (Baseline), yuvj420p, 1920x1080, 25 fps, 0.04 tbr, 1200k tbn当前没有打印视频总时长是因为这是h264裸留数据
代码剖析
void av_dump_format(AVFormatContext *ic, int index, const char *url, int is_output)
{
int i;
uint8_t *printed = ic->nb_streams ? av_mallocz(ic->nb_streams) : NULL;
if (ic->nb_streams && !printed)
return;
//如果is_output是0，说明是输入流
av_log(NULL, AV_LOG_INFO, "%s #%d, %s, %s '%s':\n",
is_output ? "Output" : "Input",
index,
is_output ? ic->oformat->name : ic->iformat->name,
is_output ? "to" : "from", url);
dump_metadata(NULL, ic->metadata, " ");
//如果is_output指定为0，开始计算视频总时长
if (!is_output) {
av_log(NULL, AV_LOG_INFO, " Duration: ");
//如果上下文中的总时长字段有效，说明不是h264裸留，h264裸留是没有dts/pts字段数据的，开始计算视频总时长
if (ic->duration != AV_NOPTS_VALUE) {
int hours, mins, secs, us;
int64_t duration = ic->duration + (ic->duration <= INT64_MAX - 5000 ? 5000 : 0);
secs = duration / AV_TIME_BASE;
us = duration % AV_TIME_BASE;
mins = secs / 60;
secs %= 60;
hours = mins / 60;
mins %= 60;
av_log(NULL, AV_LOG_INFO, "%02d:%02d:%02d.%02d", hours, mins, secs,
(100 * us) / AV_TIME_BASE);
} else {
av_log(NULL, AV_LOG_INFO, "N/A");
}
//判断开始是否开始时间有效
if (ic->start_time != AV_NOPTS_VALUE) {
int secs, us;
av_log(NULL, AV_LOG_INFO, ", start: ");
secs = llabs(ic->start_time / AV_TIME_BASE);
us = llabs(ic->start_time % AV_TIME_BASE);
av_log(NULL, AV_LOG_INFO, "%s%d.%06d",
ic->start_time >= 0 ? "" : "-",
secs,
(int) av_rescale(us, 1000000, AV_TIME_BASE));
}
av_log(NULL, AV_LOG_INFO, ", bitrate: ");
if (ic->bit_rate)
av_log(NULL, AV_LOG_INFO, "%"PRId64" kb/s", ic->bit_rate / 1000);
else
av_log(NULL, AV_LOG_INFO, "N/A");
av_log(NULL, AV_LOG_INFO, "\n");
}
for (i = 0; i < ic->nb_chapters; i++) {
AVChapter *ch = ic->chapters[i];
av_log(NULL, AV_LOG_INFO, " Chapter #%d:%d: ", index, i);
av_log(NULL, AV_LOG_INFO,
"start %f, ", ch->start * av_q2d(ch->time_base));
av_log(NULL, AV_LOG_INFO,
"end %f\n", ch->end * av_q2d(ch->time_base));
dump_metadata(NULL, ch->metadata, " ");
}
if (ic->nb_programs) {
int j, k, total = 0;
for (j = 0; j < ic->nb_programs; j++) {
AVDictionaryEntry *name = av_dict_get(ic->programs[j]->metadata,
"name", NULL, 0);
av_log(NULL, AV_LOG_INFO, " Program %d %s\n", ic->programs[j]->id,
name ? name->value : "");
dump_metadata(NULL, ic->programs[j]->metadata, " ");
for (k = 0; k < ic->programs[j]->nb_stream_indexes; k++) {
dump_stream_format(ic, ic->programs[j]->stream_index[k],
index, is_output);
printed[ic->programs[j]->stream_index[k]] = 1;
}
total += ic->programs[j]->nb_stream_indexes;
}
if (total < ic->nb_streams)
av_log(NULL, AV_LOG_INFO, " No Program\n");
}
for (i = 0; i < ic->nb_streams; i++)
if (!printed[i])
dump_stream_format(ic, i, index, is_output);
av_free(printed);
}