MediaMuxer的jni代碼分析
jni方法的定義
MediaMuxer jni方法的定義在frameworks/base/media/jni/android_media_MediaMuxer.cpp中。
static const JNINativeMethod gMethods[] = {
{ "nativeAddTrack", "(J[Ljava/lang/String;[Ljava/lang/Object;)I",
(void *)android_media_MediaMuxer_addTrack },
{ "nativeSetOrientationHint", "(JI)V",
(void *)android_media_MediaMuxer_setOrientationHint},
{ "nativeSetLocation", "(JII)V",
(void *)android_media_MediaMuxer_setLocation},
{ "nativeStart", "(J)V", (void *)android_media_MediaMuxer_start},
{ "nativeWriteSampleData", "(JILjava/nio/ByteBuffer;IIJI)V",
(void *)android_media_MediaMuxer_writeSampleData },
{ "nativeStop", "(J)V", (void *)android_media_MediaMuxer_stop},
{ "nativeSetup", "(Ljava/io/FileDescriptor;I)J",
(void *)android_media_MediaMuxer_native_setup },
{ "nativeRelease", "(J)V",
(void *)android_media_MediaMuxer_native_release },
};
我們逐一看一看這些native方法的源碼。
- android_media_MediaMuxer_addTrack
static jint android_media_MediaMuxer_addTrack(
JNIEnv *env, jclass /* clazz */, jlong nativeObject, jobjectArray keys,
jobjectArray values) {
sp<MediaMuxer> muxer(reinterpret_cast<MediaMuxer *>(nativeObject));
if (muxer == NULL) {
jniThrowException(env, "java/lang/IllegalStateException",
"Muxer was not set up correctly");
return -1;
}
sp<AMessage> trackformat;
status_t err = ConvertKeyValueArraysToMessage(env, keys, values,
&trackformat);
if (err != OK) {
jniThrowException(env, "java/lang/IllegalArgumentException",
"ConvertKeyValueArraysToMessage got an error");
return err;
}
// Return negative value when errors happen in addTrack.
jint trackIndex = muxer->addTrack(trackformat);
if (trackIndex < 0) {
jniThrowException(env, "java/lang/IllegalStateException",
"Failed to add the track to the muxer");
return -1;
}
return trackIndex;
}
首先,用nativeObject生成一個MediaMuxer(stagefright中,如無特別說明,下同)的強引用計數,如果muxer爲NULL,拋出IllegalStateException。調用ConvertKeyValueArraysToMessage把keys和values數組,轉換爲AMessage的強引用計數trackformat,返回值保存在err中,如果err不等於OK,拋出IllegalArgumentException異常。調用MediaMuxer的addTrack方法,返回值保存在trackIndex中,如果trackIndex小於0,拋出IllegalStateException,返回-1。如果一起正常,就把trackIndex返回。
- android_media_MediaMuxer_setOrientationHint
static void android_media_MediaMuxer_setOrientationHint(
JNIEnv *env, jclass /* clazz */, jlong nativeObject, jint degrees) {
sp<MediaMuxer> muxer(reinterpret_cast<MediaMuxer *>(nativeObject));
if (muxer == NULL) {
jniThrowException(env, "java/lang/IllegalStateException",
"Muxer was not set up correctly");
return;
}
status_t err = muxer->setOrientationHint(degrees);
if (err != OK) {
jniThrowException(env, "java/lang/IllegalStateException",
"Failed to set orientation hint");
return;
}
}
用nativeObject生成一個MediaMuxer的強引用計數,如果muxer爲NULL,拋出IllegalStateException。調用MediaMuxer的setOrientationHint,並且結果保存在err中,拋出IllegalStateException。
start,stop,setLocation的定義和setOrientationHint類似。
- android_media_MediaMuxer_native_setup
static jlong android_media_MediaMuxer_native_setup(
JNIEnv *env, jclass clazz, jobject fileDescriptor,
jint format) {
int fd = jniGetFDFromFileDescriptor(env, fileDescriptor);
ALOGV("native_setup: fd %d", fd);
MediaMuxer::OutputFormat fileFormat =
static_cast<MediaMuxer::OutputFormat>(format);
sp<MediaMuxer> muxer = new MediaMuxer(fd, fileFormat);
muxer->incStrong(clazz);
return reinterpret_cast<jlong>(muxer.get());
}
根據參數fileDescriptor,獲取一個文件描述符fd,輸出文件格式就是參數foramt指定的格式。根據fd和format創建MediaMuxer的實例muxer,增加muxer的強引用計數。
- android_media_MediaMuxer_writeSampleData
static void android_media_MediaMuxer_writeSampleData(
JNIEnv *env, jclass /* clazz */, jlong nativeObject, jint trackIndex,
jobject byteBuf, jint offset, jint size, jlong timeUs, jint flags) {
sp<MediaMuxer> muxer(reinterpret_cast<MediaMuxer *>(nativeObject));
if (muxer == NULL) {
jniThrowException(env, "java/lang/IllegalStateException",
"Muxer was not set up correctly");
return;
}
// Try to convert the incoming byteBuffer into ABuffer
void *dst = env->GetDirectBufferAddress(byteBuf);
jlong dstSize;
jbyteArray byteArray = NULL;
if (dst == NULL) {
byteArray =
(jbyteArray)env->CallObjectMethod(byteBuf, gFields.arrayID);
if (byteArray == NULL) {
jniThrowException(env, "java/lang/IllegalArgumentException",
"byteArray is null");
return;
}
jboolean isCopy;
dst = env->GetByteArrayElements(byteArray, &isCopy);
dstSize = env->GetArrayLength(byteArray);
} else {
dstSize = env->GetDirectBufferCapacity(byteBuf);
}
if (dstSize < (offset + size)) {
ALOGE("writeSampleData saw wrong dstSize %lld, size %d, offset %d",
(long long)dstSize, size, offset);
if (byteArray != NULL) {
env->ReleaseByteArrayElements(byteArray, (jbyte *)dst, 0);
}
jniThrowException(env, "java/lang/IllegalArgumentException",
"sample has a wrong size");
return;
}
sp<ABuffer> buffer = new ABuffer((char *)dst + offset, size);
status_t err = muxer->writeSampleData(buffer, trackIndex, timeUs, flags);
if (byteArray != NULL) {
env->ReleaseByteArrayElements(byteArray, (jbyte *)dst, 0);
}
if (err != OK) {
jniThrowException(env, "java/lang/IllegalStateException",
"writeSampleData returned an error");
}
return;
}
GetDirectBufferAddress獲取byteBuf的共享內存地址dst,如果dst爲NULL,CallObjectMethod(byteBuf, gFields.arrayID)調用java/nio/ByteBuffer中的array方法,嘗試獲取byteArray,如果byteArray依然爲NULL,拋出IllegalArgumentException,返回。獲取byteArray中的elements和byteArray的長度。如果之前獲取的dst不爲NULL,直接獲取byteBuf的容量。如果dstSize小於offset加size的和,拋出IllegalArgumentException,如果byteArray不爲空,需要釋放它,返回。調用MediaMuxer類的writeSampleData方法。
- android_media_MediaMuxer_native_release
static void android_media_MediaMuxer_native_release(
JNIEnv* /* env */, jclass clazz, jlong nativeObject) {
sp<MediaMuxer> muxer(reinterpret_cast<MediaMuxer *>(nativeObject));
if (muxer != NULL) {
muxer->decStrong(clazz);
}
}
減少muxer的強引用計數。