如何获取Android 4.1和4.2上MediaCodec支持的colorFormats？

Question

On android 4.1 and above, I intend to get the list of colorFormats supported by a particular MediaCodec .

Android 4.3 and above provides an API ( public MediaCodecInfo getCodecInfo () ) to get the MediaCodecInfo associated with a particular instance of MediaCodec . Furthermore, I am able to call getCapabilitiesForType on this MediaCodecInfo object which will fetch me associated MediaCodecInfo.CodecCapabilities object, on which I call API colorFormats to get the list of color-formats for my MediaCodec object.

Now, I'm not able to execute above sequence of calls on android 4.1 and 4.2 simply because the MediaCodec API getCodecInfo() is added in API level 18.

Could anyone suggest how can I achieve the same OR any other method to get the list of color-formats on android 4.1 and 4.2.

Answer 1

For Android 4.1 and 4.2, you need to use the MediaCodecList class to iterate through the available codecs - there you'll get the MediaCodecInfo that will provide the same information as getCodecInfo() does.

The only case where getCodecInfo() (or getName() ) is needed if you've created the codec using createEncoderByType (or createDecoderByType ) in which case you don't know which codec you're actually dealing with. At least in AOSP, both of these functions just return the first codec in MediaCodecList that matches the provided MIME type. (Some manufacturers might of course have customized this but I don't see much reason for it.)

Thus - on 4.1 and 4.2 - instead of using createEncoderByType , manually iterate through the codecs in MediaCodecList and pick the first one matching your MIME type, and get the info and capabilities there.

So, simply put - if you currently have this code:

MediaCodec codec = MediaCodec.createEncoderByType(mimeType);
MediaCodecInfo info = codec.getCodecInfo();

Then the equivalent version that supports 4.1 and 4.2 as well is:

MediaCodecInfo info = null;
for (int i = 0; i < MediaCodecList.getCodecCount() && info == null; i++) {
    MediaCodecInfo curInfo = MediaCodecList.getCodecInfoAt(i);
    if (!curInfo.isEncoder())
        continue;
    String[] types = curInfo.getSupportedTypes();
    for (int j = 0; j < types.length; j++)
        if (types[j].equals(mimeType))
            info = curInfo;
}
MediaCodec codec = MediaCodec.createByCodecName(info.getName());

Answer 2

Turns out there is an elegant way to get the color-format supported by the particular MediaCodec instance in use, that works on android 4.1 and above. Same is explained below:

While doing dequeueOutputBuffer look out for error-code: MediaCodec.INFO_OUTPUT_FORMAT_CHANGED . Upon receiving this error code, call getOutputFormat on the codec and subsequently call getInteger on the received MediaFormat object with string KEY_COLOR_FORMAT to get the color-format.