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MediaMuxer的jni代码分析
jni方法的定义
MediaMuxer jni方法的定义在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 },
};
我们逐一看一看这些native方法的源码。
- 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生成一个MediaMuxer（stagefright中，如无特别说明，下同)的强引用计数，如果muxer为NULL，抛出IllegalStateException。调用ConvertKeyValueArraysToMessage把keys和values数组，转换为AMessage的强引用计数trackformat，返回值保存在err中，如果err不等于OK，抛出IllegalArgumentException异常。调用MediaMuxer的addTrack方法，返回值保存在trackIndex中，如果trackIndex小于0，抛出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生成一个MediaMuxer的强引用计数,如果muxer为NULL，抛出IllegalStateException。调用MediaMuxer的setOrientationHint，并且结果保存在err中，抛出IllegalStateException。
start，stop，setLocation的定义和setOrientationHint类似。
- 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());
}
根据参数fileDescriptor，获取一个文件描述符fd，输出文件格式就是参数foramt指定的格式。根据fd和format创建MediaMuxer的实例muxer，增加muxer的强引用计数。
- 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获取byteBuf的共享内存地址dst，如果dst为NULL，CallObjectMethod(byteBuf, gFields.arrayID)调用java/nio/ByteBuffer中的array方法，尝试获取byteArray，如果byteArray依然为NULL，抛出IllegalArgumentException，返回。获取byteArray中的elements和byteArray的长度。如果之前获取的dst不为NULL，直接获取byteBuf的容量。如果dstSize小于offset加size的和，抛出IllegalArgumentException，如果byteArray不为空，需要释放它，返回。调用MediaMuxer类的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);
}
}
减少muxer的强引用计数。