Android多媒体开发需要添加FFmpeg支持，其实其步骤在前面Android Media Framework学习的一系列文章中就有讲述，《支持格式扩展》这篇文章已经讲完了Android多媒体需要扩展支持其他格式的步骤，这篇文章具体讲述Android怎么支持FFmpeg。
参考文章有两篇，分别是：文章一，文章二
1.Sniffer
音视频的解码播放是从探测文件格式开始的，即在DataSource.cpp中通过Sniff探测文件格式，扩展FFmpeg也是一样的，先要在DataSource中加入相应的Sniff。
DataSource通过RegisterDefaultSniffers给每一种格式添加相应的sniffer。
// static
void DataSource::RegisterDefaultSniffers() {
Mutex::Autolock autoLock(gSnifferMutex);
if (gSniffersRegistered) {
return;
}
RegisterSniffer_l(SniffMPEG4);
RegisterSniffer_l(SniffMatroska);
RegisterSniffer_l(SniffOgg);
RegisterSniffer_l(SniffWAV);
RegisterSniffer_l(SniffFLAC);
RegisterSniffer_l(SniffAMR);
RegisterSniffer_l(SniffMPEG2TS);
RegisterSniffer_l(SniffMP3);
RegisterSniffer_l(SniffAAC);
RegisterSniffer_l(SniffMPEG2PS);
RegisterSniffer_l(SniffWVM);
RegisterSnifferPlugin();
char value[PROPERTY_VALUE_MAX];
if (property_get("drm.service.enabled", value, NULL)
&& (!strcmp(value, "1") || !strcasecmp(value, "true"))) {
RegisterSniffer_l(SniffDRM);
}
//RegisterSniffer_l(SniffASF);
//RegisterSniffer_l(SniffNVAVI);
gSniffersRegistered = true;
}
这里，我们需要关注的是RegisterSnifferPlugin()。
// static
void DataSource::RegisterSnifferPlugin() {
static void (*getExtractorPlugin)(MediaExtractor::Plugin *) =
(void (*)(MediaExtractor::Plugin *))loadExtractorPlugin();
MediaExtractor::Plugin *plugin = MediaExtractor::getPlugin();
if (!plugin->sniff && getExtractorPlugin) {
getExtractorPlugin(plugin);
}
if (plugin->sniff) {
RegisterSniffer_l(plugin->sniff);
}
}
我们看到，RegisterSnifferPlugin()中有个loadExtractorPlugin()方法，具体看它的实现。
static void *loadExtractorPlugin() {
void *ret = NULL;
char lib[PROPERTY_VALUE_MAX];
if (property_get("media.stagefright.extractor-plugin", lib, "libFFmpegExtractor.so")) {
if (void *extractorLib = ::dlopen(lib, RTLD_LAZY)) {
ret = ::dlsym(extractorLib, "getExtractorPlugin");
ALOGW_IF(!ret, "Failed to find symbol, dlerror: %s", ::dlerror());
} else {
ALOGV("Failed to load %s, dlerror: %s", lib, ::dlerror());
}
}
return ret;
}
可以看到，也就是在loadExtractorPlugin()方法加载了libFFmpegExtractor.so库。
2.Extractor
扩展了FFmpeg的sniffer，接下来就是创建FFmpegExtractor实例，如果不明白可以回头看看Android Media Framework的相关文章。
MediaExtractor管理着各种具体的Extractor，FFmpegExtractor也不例外。在上面的loadExtractorPlugin()方法中调用的是FFmpegExtractor的getExtractorPlugin()方法，看看具体实现：
extern "C" void getExtractorPlugin(android::MediaExtractor::Plugin *plugin)
{
plugin->sniff = android::SniffFFMPEG;
plugin->create = android::CreateFFmpegExtractor;
}
很好理解，就是指明SniffFFMPEG并调用CreateFFmpegExtractor。其中SniffFFMPEG()方法就是通过设置confidence值来指定格式，我自己项目中的比较复杂，这里贴下文章二中的代码：
bool SniffFFMPEG( const sp &source, String8 *mimeType,
float *confidence, sp *) {
LOGD("SniffFFMPEG: confidence force to be 1.0");
// QGC: ffmpeg force to be high confidence
*mimeType = MEDIA_MIMETYPE_CONTAINER_FFMPEG;
*confidence = 1.0f;
return true;
}
相当暴力，直接指定*confidence = 1.0f。
CreateFFmpegExtractor顾名思义就是创建FFmpegExtractor的实例。
MediaExtractor *CreateFFmpegExtractor(const sp &source, const char *mime, const sp &meta) {
MediaExtractor *ret = NULL;
AString notuse;
if (meta.get() && meta->findString("extended-extractor", ¬use) && (
!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_MPEG) ||
!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_AAC) ||
!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_VORBIS) ||
!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_FLAC) ||
!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_AC3) ||
!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_APE) ||
!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_DTS) ||
!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_MPEG_LAYER_II) ||
!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_RA) ||
!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_WMA) ||
!strcasecmp(mime, MEDIA_MIMETYPE_AUDIO_FFMPEG) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MPEG4) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MOV) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MATROSKA) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_TS) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MPEG2PS) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_AVI) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_ASF) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_WEBM) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_WMV) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MPG) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_FLV) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_DIVX) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_RM) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_WAV) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_FLAC) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_APE) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_DTS) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_MP2) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_RA) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_OGG) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_VC1) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_HEVC) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_WMA) ||
!strcasecmp(mime, MEDIA_MIMETYPE_CONTAINER_FFMPEG))) {
ALOGV("media format %s", mime);
bool audio_only = false;
if (!strncmp(mime, "audio/", 6)) {
ALOGV("set audio only mode");
audio_only = true;
}
ret = new FFmpegExtractor(source, meta, audio_only);
}
ALOGD("%ssupported mime: %s", (ret ? "" : "un"), mime);
return ret;
}
这个方法用到的 meta->findString("extended-extractor", ¬use)其实就在SniffFFMPEG中指定（当然上边的SniffFFMPEG没有），这里给出：
(*meta)->setString("extended-extractor", "extended-extractor");
(*meta)->setString("extended-extractor-subtype", "ffmpegextractor");
(*meta)->setString("extended-extractor-mime", container);
3.kComponents
kComponents数组指定的是系统支持的编解码器，当然要加上FFmpeg的相关东西。
static const struct {
const char *mName;
const char *mLibNameSuffix;
const char *mRole;
} kComponents[] = {
{ "OMX.ffmpeg.mpeg2v.decoder", "ffmpegvdec", "video_decoder.mpeg2v" },
{ "OMX.ffmpeg.h263.decoder", "ffmpegvdec", "video_decoder.h263" },
{ "OMX.ffmpeg.mpeg4.decoder", "ffmpegvdec", "video_decoder.mpeg4" },
{ "OMX.ffmpeg.wmv.decoder", "ffmpegvdec", "video_decoder.wmv" },
{ "OMX.ffmpeg.rv.decoder", "ffmpegvdec", "video_decoder.rv" },
{ "OMX.ffmpeg.h264.decoder", "ffmpegvdec", "video_decoder.avc" },
{ "OMX.ffmpeg.vp8.decoder", "ffmpegvdec", "video_decoder.vp8" },
{ "OMX.ffmpeg.vc1.decoder", "ffmpegvdec", "video_decoder.vc1" },
{ "OMX.ffmpeg.flv1.decoder", "ffmpegvdec", "video_decoder.flv1" },
{ "OMX.ffmpeg.divx.decoder", "ffmpegvdec", "video_decoder.divx" },
{ "OMX.ffmpeg.hevc.decoder", "ffmpegvdec", "video_decoder.hevc" },
{ "OMX.ffmpeg.vtrial.decoder", "ffmpegvdec", "video_decoder.trial" },
{ "OMX.ffmpeg.aac.decoder", "ffmpegadec", "audio_decoder.aac" },
{ "OMX.ffmpeg.mp3.decoder", "ffmpegadec", "audio_decoder.mp3" },
{ "OMX.ffmpeg.vorbis.decoder", "ffmpegadec", "audio_decoder.vorbis" },
{ "OMX.ffmpeg.wma.decoder", "ffmpegadec", "audio_decoder.wma" },
{ "OMX.ffmpeg.ra.decoder", "ffmpegadec", "audio_decoder.ra" },
{ "OMX.ffmpeg.flac.decoder", "ffmpegadec", "audio_decoder.flac" },
{ "OMX.ffmpeg.mp2.decoder", "ffmpegadec", "audio_decoder.mp2" },
{ "OMX.ffmpeg.ac3.decoder", "ffmpegadec", "audio_decoder.ac3" },
{ "OMX.ffmpeg.ape.decoder", "ffmpegadec", "audio_decoder.ape" },
{ "OMX.ffmpeg.dts.decoder", "ffmpegadec", "audio_decoder.dts" },
{ "OMX.ffmpeg.atrial.decoder", "ffmpegadec", "audio_decoder.trial" },
{ "OMX.google.aac.decoder", "aacdec", "audio_decoder.aac" },
{ "OMX.google.aac.encoder", "aacenc", "audio_encoder.aac" },
{ "OMX.google.amrnb.decoder", "amrdec", "audio_decoder.amrnb" },
{ "OMX.google.amrnb.encoder", "amrnbenc", "audio_encoder.amrnb" },
{ "OMX.google.amrwb.decoder", "amrdec", "audio_decoder.amrwb" },
{ "OMX.google.amrwb.encoder", "amrwbenc", "audio_encoder.amrwb" },
{ "OMX.google.h264.decoder", "h264dec", "video_decoder.avc" },
{ "OMX.google.h264.encoder", "h264enc", "video_encoder.avc" },
{ "OMX.google.g711.alaw.decoder", "g711dec", "audio_decoder.g711alaw" },
{ "OMX.google.g711.mlaw.decoder", "g711dec", "audio_decoder.g711mlaw" },
{ "OMX.google.h263.decoder", "mpeg4dec", "video_decoder.h263" },
{ "OMX.google.h263.encoder", "mpeg4enc", "video_encoder.h263" },
{ "OMX.google.mpeg4.decoder", "mpeg4dec", "video_decoder.mpeg4" },
{ "OMX.google.mpeg4.encoder", "mpeg4enc", "video_encoder.mpeg4" },
{ "OMX.google.mp3.decoder", "mp3dec", "audio_decoder.mp3" },
{ "OMX.google.vorbis.decoder", "vorbisdec", "audio_decoder.vorbis" },
{ "OMX.google.vp8.decoder", "vpxdec", "video_decoder.vp8" },
{ "OMX.google.vp9.decoder", "vpxdec", "video_decoder.vp9" },
{ "OMX.google.vp8.encoder", "vpxenc", "video_encoder.vp8" },
{ "OMX.google.raw.decoder", "rawdec", "audio_decoder.raw" },
{ "OMX.google.flac.encoder", "flacenc", "audio_encoder.flac" },
{ "OMX.google.gsm.decoder", "gsmdec", "audio_decoder.gsm" },
};
"OMX.google."开头的是Android本身支持的，"OMX.ffmpeg."开头的是FFmpeg的。
4.media_codecs.xml
最后，在/etc/media_codecs.xml中配置自己需要的编解码器。
当然，要想完整的添加FFmpeg，还有很多头文件需要加，有的文件代码也需要稍许修改，但整个脉络是这样的。