我正在尝试使用 4.2 中引入的 Android MediaCodec API 重新编码具有不同比特率的 h.264 mp4 文件。
我可以使用 MediaCodec API 解码和播放内容（在更改比特率之前），但是如果我尝试在解码之前用不同的比特率重新编码内容，我会得到乱码（一个灰色的绿色屏幕像素化）。
我使用的代码基于 Android 测试用例 android.media.cts.DecoderTest Android 测试用例 android.media.cts.DecoderTest：
public void encodeDecodeVideoFile(AssetFileDescriptor assetFileDescriptor) {
int bitRate = 500000;
int frameRate = 30;
int width = 480;
int height = 368;
String mimeType = "video/avc";
MediaCodec encoder, decoder = null;
ByteBuffer[] encoderInputBuffers;
ByteBuffer[] encoderOutputBuffers;
ByteBuffer[] decoderInputBuffers = null;
ByteBuffer[] decoderOutputBuffers = null;
// Find a code that supports the mime type
int numCodecs = MediaCodecList.getCodecCount();
MediaCodecInfo codecInfo = null;
for (int i = 0; i < numCodecs && codecInfo == null; i++) {
MediaCodecInfo info = MediaCodecList.getCodecInfoAt(i);
if (!info.isEncoder()) {
continue;
}
String[] types = info.getSupportedTypes();
boolean found = false;
for (int j = 0; j < types.length && !found; j++) {
if (types[j].equals(mimeType))
found = true;
}
if (!found)
continue;
codecInfo = info;
}
Log.d(TAG, "Found " + codecInfo.getName() + " supporting " + mimeType);
// Find a color profile that the codec supports
int colorFormat = 0;
MediaCodecInfo.CodecCapabilities capabilities = codecInfo.getCapabilitiesForType(mimeType);
for (int i = 0; i < capabilities.colorFormats.length && colorFormat == 0; i++) {
int format = capabilities.colorFormats[i];
switch (format) {
case MediaCodecInfo.CodecCapabilities.COLOR_FormatYUV420Planar:
case MediaCodecInfo.CodecCapabilities.COLOR_FormatYUV420PackedPlanar:
case MediaCodecInfo.CodecCapabilities.COLOR_FormatYUV420SemiPlanar:
case MediaCodecInfo.CodecCapabilities.COLOR_FormatYUV420PackedSemiPlanar:
case MediaCodecInfo.CodecCapabilities.COLOR_TI_FormatYUV420PackedSemiPlanar:
colorFormat = format;
break;
default:
Log.d(TAG, "Skipping unsupported color format " + format);
break;
}
}
Log.d(TAG, "Using color format " + colorFormat);
// Determine width, height and slice sizes
if (codecInfo.getName().equals("OMX.TI.DUCATI1.VIDEO.H264E")) {
// This codec doesn't support a width not a multiple of 16,
// so round down.
width &= ~15;
}
int stride = width;
int sliceHeight = height;
if (codecInfo.getName().startsWith("OMX.Nvidia.")) {
stride = (stride + 15) / 16 * 16;
sliceHeight = (sliceHeight + 15) / 16 * 16;
}
// Used MediaExtractor to select the first track from the h.264 content
MediaExtractor extractor = new MediaExtractor();
extractor.setDataSource(assetFileDescriptor.getFileDescriptor(), assetFileDescriptor.getStartOffset(), assetFileDescriptor.getLength());
MediaFormat extractedFormat = extractor.getTrackFormat(0);
String mime = extractedFormat.getString(MediaFormat.KEY_MIME);
Log.d(TAG, "Extartced Mime " + mime);
extractor.selectTrack(0);
// Create an encoder
encoder = MediaCodec.createByCodecName(codecInfo.getName());
MediaFormat inputFormat = MediaFormat.createVideoFormat(mimeType, width, height);
inputFormat.setInteger(MediaFormat.KEY_BIT_RATE, bitRate);
inputFormat.setInteger(MediaFormat.KEY_FRAME_RATE, frameRate);
inputFormat.setInteger(MediaFormat.KEY_COLOR_FORMAT, colorFormat);
inputFormat.setInteger(MediaFormat.KEY_I_FRAME_INTERVAL, 5);
inputFormat.setInteger("stride", stride);
inputFormat.setInteger("slice-height", sliceHeight);
Log.d(TAG, "Configuring encoder with input format " + inputFormat);
encoder.configure(inputFormat, null /* surface */, null /* crypto */, MediaCodec.CONFIGURE_FLAG_ENCODE);
encoder.start();
encoderInputBuffers = encoder.getInputBuffers();
encoderOutputBuffers = encoder.getOutputBuffers();
// start encoding + decoding
final long kTimeOutUs = 5000;
MediaCodec.BufferInfo info = new MediaCodec.BufferInfo();
boolean sawInputEOS = false;
boolean sawOutputEOS = false;
MediaFormat oformat = null;
long startMs = System.currentTimeMillis();
while (!sawOutputEOS) {
if (!sawInputEOS) {
int inputBufIndex = encoder.dequeueInputBuffer(kTimeOutUs);
if (inputBufIndex >= 0) {
ByteBuffer dstBuf = encoderInputBuffers[inputBufIndex];
int sampleSize = extractor.readSampleData(dstBuf, 0 /* offset */);
long presentationTimeUs = 0;
if (sampleSize < 0) {
Log.d(TAG, "saw input EOS.");
sawInputEOS = true;
sampleSize = 0;
} else {
presentationTimeUs = extractor.getSampleTime();
}
encoder.queueInputBuffer(inputBufIndex, 0 /* offset */, sampleSize, presentationTimeUs, sawInputEOS ? MediaCodec.BUFFER_FLAG_END_OF_STREAM : 0);
if (!sawInputEOS) {
extractor.advance();
}
}
}
int res = encoder.dequeueOutputBuffer(info, kTimeOutUs);
if (res >= 0) {
int outputBufIndex = res;
ByteBuffer buf = encoderOutputBuffers[outputBufIndex];
buf.position(info.offset);
buf.limit(info.offset + info.size);
if ((info.flags & MediaCodec.BUFFER_FLAG_CODEC_CONFIG) != 0) {
// create a decoder
decoder = MediaCodec.createDecoderByType(mimeType);
MediaFormat format = MediaFormat.createVideoFormat(mimeType, width, height);
format.setInteger(MediaFormat.KEY_COLOR_FORMAT, colorFormat);
format.setByteBuffer("csd-0", buf);
decoder.configure(format, surface /* surface */, null /* crypto */, 0 /* flags */);
decoder.start();
decoderInputBuffers = decoder.getInputBuffers();
decoderOutputBuffers = decoder.getOutputBuffers();
} else {
int decIndex = decoder.dequeueInputBuffer(-1);
decoderInputBuffers[decIndex].clear();
decoderInputBuffers[decIndex].put(buf);
decoder.queueInputBuffer(decIndex, 0, info.size, info.presentationTimeUs, info.flags);
}
encoder.releaseOutputBuffer(outputBufIndex, false /* render */);
} else if (res == MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED) {
encoderOutputBuffers = encoder.getOutputBuffers();
Log.d(TAG, "encoder output buffers have changed.");
} else if (res == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED) {
MediaFormat encformat = encoder.getOutputFormat();
Log.d(TAG, "encoder output format has changed to " + encformat);
}
if (decoder == null)
res = MediaCodec.INFO_TRY_AGAIN_LATER;
else
res = decoder.dequeueOutputBuffer(info, kTimeOutUs);
if (res >= 0) {
int outputBufIndex = res;
ByteBuffer buf = decoderOutputBuffers[outputBufIndex];
buf.position(info.offset);
buf.limit(info.offset + info.size);
// The worlds simplest FPS implementation
while (info.presentationTimeUs / 1000 > System.currentTimeMillis() - startMs) {
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
break;
}
}
decoder.releaseOutputBuffer(outputBufIndex, true /* render */);
if ((info.flags & MediaCodec.BUFFER_FLAG_END_OF_STREAM) != 0) {
Log.d(TAG, "saw output EOS.");
sawOutputEOS = true;
}
} else if (res == MediaCodec.INFO_OUTPUT_BUFFERS_CHANGED) {
decoderOutputBuffers = decoder.getOutputBuffers();
Log.d(TAG, "decoder output buffers have changed.");
} else if (res == MediaCodec.INFO_OUTPUT_FORMAT_CHANGED) {
oformat = decoder.getOutputFormat();
Log.d(TAG, "decoder output format has changed to " + oformat);
}
}
encoder.stop();
encoder.release();
decoder.stop();
decoder.release();
}
我要编码的文件来自 Android cts 测试项目：
R.raw.video_480x360_mp4_h264_1000kbps_30fps_aac_stereo_128kbps_44100hz
我猜这个问题与我在编码器 MediaCodec 中指定的格式参数有关，但我无法弄清楚什么是不正确/缺失的。