Support gapless playback for mp3 and m4a

Gapless playback for appropriately tagged mp3 and m4a files.
Currently this is implemented in OMXCodec, which most players
use, but should be easy to support in other players as well by
using the SkipCutBuffer utility class.

Change-Id: I748c669adc1cfbe5ee9a7dea2fad945d48882551

1 files changed, 130 insertions, 0 deletions

diff --git a/media/libstagefright/SkipCutBuffer.cpp b/media/libstagefright/SkipCutBuffer.cpp
new file mode 100755
index 0000000..6d331b0
--- /dev/null
+++ b/media/libstagefright/SkipCutBuffer.cpp
@@ -0,0 +1,130 @@
+/*
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+//#define LOG_NDEBUG 0
+#define LOG_TAG "SkipCutBuffer"
+#include <utils/Log.h>
+
+#include <media/stagefright/foundation/ADebug.h>
+#include <media/stagefright/MediaBuffer.h>
+#include <media/stagefright/SkipCutBuffer.h>
+
+namespace android {
+
+SkipCutBuffer::SkipCutBuffer(int32_t skip, int32_t cut, int32_t output_size) {
+    mFrontPadding = skip;
+    mBackPadding = cut;
+    mWriteHead = 0;
+    mReadHead = 0;
+    mCapacity = cut + output_size;
+    mCutBuffer = new char[mCapacity];
+    ALOGV("skipcutbuffer %d %d %d", skip, cut, mCapacity);
+}
+
+SkipCutBuffer::~SkipCutBuffer() {
+    delete[] mCutBuffer;
+}
+
+void SkipCutBuffer::submit(MediaBuffer *buffer) {
+    int32_t offset = buffer->range_offset();
+    int32_t buflen = buffer->range_length();
+
+    // drop the initial data from the buffer if needed
+    if (mFrontPadding > 0) {
+        // still data left to drop
+        int32_t to_drop = (buflen < mFrontPadding) ? buflen : mFrontPadding;
+        offset += to_drop;
+        buflen -= to_drop;
+        buffer->set_range(offset, buflen);
+        mFrontPadding -= to_drop;
+    }
+
+
+    // append data to cutbuffer
+    char *src = ((char*) buffer->data()) + offset;
+    write(src, buflen);
+
+
+    // the mediabuffer is now empty. Fill it from cutbuffer, always leaving
+    // at least mBackPadding bytes in the cutbuffer
+    char *dst = (char*) buffer->data();
+    size_t copied = read(dst, buffer->size());
+    buffer->set_range(0, copied);
+}
+
+void SkipCutBuffer::clear() {
+    mWriteHead = mReadHead = 0;
+}
+
+void SkipCutBuffer::write(const char *src, size_t num) {
+    int32_t sizeused = (mWriteHead - mReadHead);
+    if (sizeused < 0) sizeused += mCapacity;
+
+    // everything must fit
+    CHECK_GE((mCapacity - size_t(sizeused)), num);
+
+    size_t copyfirst = (mCapacity - mWriteHead);
+    if (copyfirst > num) copyfirst = num;
+    if (copyfirst) {
+        memcpy(mCutBuffer + mWriteHead, src, copyfirst);
+        num -= copyfirst;
+        src += copyfirst;
+        mWriteHead += copyfirst;
+        CHECK_LE(mWriteHead, mCapacity);
+        if (mWriteHead == mCapacity) mWriteHead = 0;
+        if (num) {
+            memcpy(mCutBuffer, src, num);
+            mWriteHead += num;
+        }
+    }
+}
+
+size_t SkipCutBuffer::read(char *dst, size_t num) {
+    int32_t available = (mWriteHead - mReadHead);
+    if (available < 0) available += mCapacity;
+
+    available -= mBackPadding;
+    if (available <=0) {
+        return 0;
+    }
+    if (available < num) {
+        num = available;
+    }
+
+    size_t copyfirst = (mCapacity - mReadHead);
+    if (copyfirst > num) copyfirst = num;
+    if (copyfirst) {
+        memcpy(dst, mCutBuffer + mReadHead, copyfirst);
+        num -= copyfirst;
+        dst += copyfirst;
+        mReadHead += copyfirst;
+        CHECK_LE(mReadHead, mCapacity);
+        if (mReadHead == mCapacity) mReadHead = 0;
+        if (num) {
+            memcpy(dst, mCutBuffer, num);
+            mReadHead += num;
+        }
+    }
+    return available;
+}
+
+size_t SkipCutBuffer::size() {
+    int32_t available = (mWriteHead - mReadHead);
+    if (available < 0) available += mCapacity;
+    return available;
+}
+
+}  // namespace android