FFmpeg里面有一个模块FFprobe（https://ffmpeg.org/ffprobe.html）专门用来检测多媒体格式数据，它的作用类似Android中的MediaMetadataRetriever。FFprobe支持检测format、streams、frames，用法与FFmpeg类似，我们可以单独使用，也可以结合在一起使用，下面举例说明一下：
1、format
仅是显示format：ffprobe -i xxx.mp4 -show_format
既显示又打印format：ffprobe -i xxx.mp4 -show_format -print_format json
2、streams
显示音视频流：ffprobe -i xxx.mp4 -show_streams
3、frames
显示视频帧：ffprobe -i xxx.mp4 -show_frames
4、format与streams
ffprobe -i xxx.mp4 -show_streams -show_format -print_format json
最终打印出来是json格式(也可以选择xml格式)，我们需要解析一下json数据，提取我们需要的信息，最终数据如下图：
看到上图，伙伴们有木有恍然大悟，感觉到与Android的MediaMetadataRetriever的功能似曾相识呢？FFprobe可以检测的多媒体信息包括：时长、码率、文件大小、封装格式、多媒体流的个数、视频分辨率、宽高比、像素格式、帧率、视频编码器、音频采样率、声道个数、声道布局、音频编码器等等。它比Android自带的MediaMetadataRetriever的优势在于：ffprobe可支持更多多媒体格式，兼容性好；而MediaMetadataRetriever取决于系统的硬解码器，不同手机的MediaCodec编解码能力存在差异。下面我们来具体讨论下FFprobe检测多媒体信息的实现过程：
一、修改ffprobe源码
在ffprobe.c源码中，是没有对外方法提供jni调用的，也没有返回字符串结果。所以我们需要修改下ffprobe.c源码：首先把main方法改为ffprobe_run方法，并且在ffprobe.h里面声明该方法，然后增加字符串打印方法。
//ffprobe主函数入口
char* ffprobe_run(int argc, char **argv)
{
const Writer *w;
WriterContext *wctx;
char *buf;
char *w_name = NULL, *w_args = NULL;
int ret, i;
//动态申请内存
buffer_length = 0;
if(print_buffer == NULL) {
print_buffer = av_malloc(sizeof(char) * buffer_size);
}
memset(print_buffer, '\0', (size_t) buffer_size);
...
return print_buffer;
}编写打印json字符串方法：
void frank_printf_json(char *fmt, ...)
{
va_list args;
va_start(args, fmt);
int length = printf_json(print_buffer + buffer_length, buffer_size - buffer_length, fmt, args);
buffer_length += length;
va_end(args);
}在解析多媒体格式时，调用打印json字符串方法，把数据写入内存里：
static void json_print_section_header(WriterContext *wctx)
{
JSONContext *json = wctx->priv;
AVBPrint buf;
const struct section *section = wctx->section[wctx->level];
const struct section *parent_section = wctx->level ?
wctx->section[wctx->level-1] : NULL;
if (wctx->level && wctx->nb_item[wctx->level-1])
frank_printf_json(",\n");
if (section->flags & SECTION_FLAG_IS_WRAPPER) {
frank_printf_json("{\n");
json->indent_level++;
} else {
av_bprint_init(&buf, 1, AV_BPRINT_SIZE_UNLIMITED);
json_escape_str(&buf, section->name, wctx);
JSON_INDENT();
json->indent_level++;
if (section->flags & SECTION_FLAG_IS_ARRAY) {
frank_printf_json("\"%s\": [\n", buf.str);
} else if (parent_section && !(parent_section->flags & SECTION_FLAG_IS_ARRAY)) {
frank_printf_json("\"%s\": {%s", buf.str, json->item_start_end);
} else {
frank_printf_json("{%s", json->item_start_end);
/* this is required so the parser can distinguish between packets and frames */
if (parent_section && parent_section->id == SECTION_ID_PACKETS_AND_FRAMES) {
if (!json->compact)
JSON_INDENT();
frank_printf_json("\"type\": \"%s\"%s", section->name, json->item_sep);
}
}
av_bprint_finalize(&buf, NULL);
}
}
static void json_print_section_footer(WriterContext *wctx)
{
JSONContext *json = wctx->priv;
const struct section *section = wctx->section[wctx->level];
if (wctx->level == 0) {
json->indent_level--;
frank_printf_json("\n}\n");
} else if (section->flags & SECTION_FLAG_IS_ARRAY) {
frank_printf_json("\n");
json->indent_level--;
JSON_INDENT();
frank_printf_json("]");
} else {
frank_printf_json("%s", json->item_start_end);
json->indent_level--;
if (!json->compact)
JSON_INDENT();
frank_printf_json("}");
}
}
static inline void json_print_item_str(WriterContext *wctx,
const char *key, const char *value)
{
AVBPrint buf;
av_bprint_init(&buf, 1, AV_BPRINT_SIZE_UNLIMITED);
frank_printf_json("\"%s\":", json_escape_str(&buf, key, wctx));
av_bprint_clear(&buf);
frank_printf_json(" \"%s\"", json_escape_str(&buf, value, wctx));
av_bprint_finalize(&buf, NULL);
}
static void json_print_str(WriterContext *wctx, const char *key, const char *value)
{
JSONContext *json = wctx->priv;
if (wctx->nb_item[wctx->level])
frank_printf_json("%s", json->item_sep);
if (!json->compact)
JSON_INDENT();
json_print_item_str(wctx, key, value);
}
static void json_print_int(WriterContext *wctx, const char *key, long long int value)
{
JSONContext *json = wctx->priv;
AVBPrint buf;
if (wctx->nb_item[wctx->level])
frank_printf_json("%s", json->item_sep);
if (!json->compact)
JSON_INDENT();
av_bprint_init(&buf, 1, AV_BPRINT_SIZE_UNLIMITED);
frank_printf_json("\"%s\": %lld", json_escape_str(&buf, key, wctx), value);
av_bprint_finalize(&buf, NULL);
}二、封装jni方法
提供jni方法，供java层调用ffprobe_run()，实现多媒体格式的解析：
FFMPEG_FUNC(jstring , handleProbe, jobjectArray commands) {
int argc = (*env)->GetArrayLength(env, commands);
char **argv = (char**)malloc(argc * sizeof(char*));
int i;
for (i = 0; i < argc; i++) {
jstring jstr = (jstring) (*env)->GetObjectArrayElement(env, commands, i);
char* temp = (char*) (*env)->GetStringUTFChars(env, jstr, 0);
argv[i] = malloc(1024);
strcpy(argv[i], temp);
(*env)->ReleaseStringUTFChars(env, jstr, temp);
}
//execute ffprobe command
char* result = ffprobe_run(argc, argv);
//release memory
for (i = 0; i < argc; i++) {
free(argv[i]);
}
free(argv);
return (*env)->NewStringUTF(env, result);
}三、java层调用jni方法
在java层使用native关键字声明jni方法，开启子线程调用：
/**
* execute probe cmd internal
* @param commands commands
* @param onHandleListener onHandleListener
*/
public static void executeProbe(final String[] commands, final OnHandleListener onHandleListener) {
new Thread(new Runnable() {
@Override
public void run() {
if(onHandleListener != null) {
onHandleListener.onBegin();
}
//execute ffprobe
String result = handleProbe(commands);
int resultCode = !TextUtils.isEmpty(result) ? RESULT_SUCCESS : RESULT_ERROR;
if(onHandleListener != null) {
onHandleListener.onEnd(resultCode, result);
}
}
}).start();
}
private native static String handleProbe(String[] commands);四、监听FFprobe运行状态
传入字符串参数，调用executeFFprobeCmd方法，实现onHandlerListener监听：
/**
* execute probe cmd
* @param commandLine commandLine
*/
public void executeFFprobeCmd(final String[] commandLine) {
if(commandLine == null) {
return;
}
FFmpegCmd.executeProbe(commandLine, new OnHandleListener() {
@Override
public void onBegin() {
mHandler.obtainMessage(MSG_BEGIN).sendToTarget();
}
@Override
public void onEnd(int resultCode, String resultMsg) {
MediaBean mediaBean = null;
if(resultMsg != null && !resultMsg.isEmpty()) {
mediaBean = JsonParseTool.parseMediaFormat(resultMsg);
}
mHandler.obtainMessage(MSG_FINISH, mediaBean).sendToTarget();
}
});
}五、封装FFprobe命令
在文章的开头，我们已经介绍过ffprobe命令，更多更详细的命令请参考文档:https://ffmpeg.org/ffprobe.html.ffprobe命令结构分为三部分：ffprobe+(-i filePath)输入文件路径+(-show_streams -show_frames -show_format)执行主体。
public static String[] probeFormat(String inputFile) {
String ffprobeCmd = "ffprobe -i %s -show_streams -show_format -print_format json";
ffprobeCmd = String.format(Locale.getDefault(), ffprobeCmd, inputFile);
return ffprobeCmd.split(" ");
}六、解析json数据
调用FFprobe函数，返回json字符串结果后，我们需要进一步解析，提取我们需要的信息：
public static MediaBean parseMediaFormat(String mediaFormat) {
if (mediaFormat == null || mediaFormat.isEmpty()) {
return null;
}
MediaBean mediaBean = null;
try {
JSONObject jsonMedia = new JSONObject(mediaFormat);
JSONObject jsonMediaFormat = jsonMedia.getJSONObject("format");
mediaBean = new MediaBean();
int streamNum = jsonMediaFormat.optInt("nb_streams");
mediaBean.setStreamNum(streamNum);
String formatName = jsonMediaFormat.optString("format_name");
mediaBean.setFormatName(formatName);
String bitRateStr = jsonMediaFormat.optString("bit_rate");
if (!TextUtils.isEmpty(bitRateStr)) {
mediaBean.setBitRate(Integer.valueOf(bitRateStr));
}
String sizeStr = jsonMediaFormat.optString("size");
if (!TextUtils.isEmpty(sizeStr)) {
mediaBean.setSize(Long.valueOf(sizeStr));
}
String durationStr = jsonMediaFormat.optString("duration");
if (!TextUtils.isEmpty(durationStr)) {
float duration = Float.valueOf(durationStr);
mediaBean.setDuration((long) duration);
}
JSONArray jsonMediaStream = jsonMedia.getJSONArray("streams");
if (jsonMediaStream == null) {
return mediaBean;
}
for (int index = 0; index < jsonMediaStream.length(); index ++) {
JSONObject jsonMediaStreamItem = jsonMediaStream.optJSONObject(index);
if (jsonMediaStreamItem == null) continue;
String codecType = jsonMediaStreamItem.optString("codec_type");
if (codecType == null) continue;
if (codecType.equals(TYPE_VIDEO)) {
VideoBean videoBean = new VideoBean();
mediaBean.setVideoBean(videoBean);
String codecName = jsonMediaStreamItem.optString("codec_tag_string");
videoBean.setVideoCodec(codecName);
int width = jsonMediaStreamItem.optInt("width");
videoBean.setWidth(width);
int height = jsonMediaStreamItem.optInt("height");
videoBean.setHeight(height);
String aspectRatio = jsonMediaStreamItem.optString("display_aspect_ratio");
videoBean.setDisplayAspectRatio(aspectRatio);
String pixelFormat = jsonMediaStreamItem.optString("pix_fmt");
videoBean.setPixelFormat(pixelFormat);
String profile = jsonMediaStreamItem.optString("profile");
videoBean.setProfile(profile);
int level = jsonMediaStreamItem.optInt("level");
videoBean.setLevel(level);
String frameRateStr = jsonMediaStreamItem.optString("r_frame_rate");
if (!TextUtils.isEmpty(frameRateStr)) {
String[] frameRateArray = frameRateStr.split("/");
double frameRate = Math.ceil(Double.valueOf(frameRateArray[0]) / Double.valueOf(frameRateArray[1]));
videoBean.setFrameRate((int) frameRate);
}
} else if (codecType.equals(TYPE_AUDIO)) {
AudioBean audioBean = new AudioBean();
mediaBean.setAudioBean(audioBean);
String codecName = jsonMediaStreamItem.optString("codec_tag_string");
audioBean.setAudioCodec(codecName);
String sampleRateStr = jsonMediaStreamItem.optString("sample_rate");
if (!TextUtils.isEmpty(sampleRateStr)) {
audioBean.setSampleRate(Integer.valueOf(sampleRateStr));
}
int channels = jsonMediaStreamItem.optInt("channels");
audioBean.setChannels(channels);
String channelLayout = jsonMediaStreamItem.optString("channel_layout");
audioBean.setChannelLayout(channelLayout);
}
}
} catch (Exception e) {
Log.e(TAG, "parse error=" + e.toString());
}
return mediaBean;
}折腾这么久，终于解析到多媒体格式相关数据了，详细源码可以到Github查看：https://github.com/xufuji456/FFmpegAndroid
