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Merge "Document CryptoInfo Settings for CENC 2016 & HLS Audio" into pi-dev

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TreeHugger Robot
2018-03-23 01:02:30 +00:00
committed by Android (Google) Code Review
parent 51856fde2b 6da8f88296
commit 6ab6a9d433
1 changed files with 70 additions and 25 deletions
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95
media/java/android/media/MediaCodec.java
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@@ -2359,17 +2359,61 @@ final public class MediaCodec {
public static final int CRYPTO_MODE_AES_CBC = 2;
/**
* Metadata describing the structure of a (at least partially) encrypted
* input sample.
* A buffer's data is considered to be partitioned into "subSamples",
* each subSample starts with a (potentially empty) run of plain,
* unencrypted bytes followed by a (also potentially empty) run of
* encrypted bytes. If pattern encryption applies, each of the latter runs
* is encrypted only partly, according to a repeating pattern of "encrypt"
* and "skip" blocks. numBytesOfClearData can be null to indicate that all
* data is encrypted. This information encapsulates per-sample metadata as
* outlined in ISO/IEC FDIS 23001-7:2011 "Common encryption in ISO base
* media file format files".
* Metadata describing the structure of an encrypted input sample.
* <p>
* A buffer's data is considered to be partitioned into "subSamples". Each subSample starts with
* a run of plain, unencrypted bytes followed by a run of encrypted bytes. Either of these runs
* may be empty. If pattern encryption applies, each of the encrypted runs is encrypted only
* partly, according to a repeating pattern of "encrypt" and "skip" blocks.
* {@link #numBytesOfClearData} can be null to indicate that all data is encrypted, and
* {@link #numBytesOfEncryptedData} can be null to indicate that all data is clear. At least one
* of {@link #numBytesOfClearData} and {@link #numBytesOfEncryptedData} must be non-null.
* <p>
* This information encapsulates per-sample metadata as outlined in ISO/IEC FDIS 23001-7:2016
* "Common encryption in ISO base media file format files".
* <p>
* <h3>ISO-CENC Schemes</h3>
* ISO/IEC FDIS 23001-7:2016 defines four possible schemes by which media may be encrypted,
* corresponding to each possible combination of an AES mode with the presence or absence of
* patterned encryption.
*
* <table style="width: 0%">
* <thead>
* <tr>
* <th>&nbsp;</th>
* <th>AES-CTR</th>
* <th>AES-CBC</th>
* </tr>
* </thead>
* <tbody>
* <tr>
* <th>Without Patterns</th>
* <td>cenc</td>
* <td>cbc1</td>
* </tr><tr>
* <th>With Patterns</th>
* <td>cens</td>
* <td>cbcs</td>
* </tr>
* </tbody>
* </table>
*
* For {@code CryptoInfo}, the scheme is selected implicitly by the combination of the
* {@link #mode} field and the value set with {@link #setPattern}. For the pattern, setting the
* pattern to all zeroes (that is, both {@code blocksToEncrypt} and {@code blocksToSkip} are
* zero) is interpreted as turning patterns off completely. A scheme that does not use patterns
* will be selected, either cenc or cbc1. Setting the pattern to any nonzero value will choose
* one of the pattern-supporting schemes, cens or cbcs. The default pattern if
* {@link #setPattern} is never called is all zeroes.
* <p>
* <h4>HLS SAMPLE-AES Audio</h4>
* HLS SAMPLE-AES audio is encrypted in a manner compatible with the cbcs scheme, except that it
* does not use patterned encryption. However, if {@link #setPattern} is used to set the pattern
* to all zeroes, this will be interpreted as selecting the cbc1 scheme. The cbc1 scheme cannot
* successfully decrypt HLS SAMPLE-AES audio because of differences in how the IVs are handled.
* For this reason, it is recommended that a pattern of {@code 1} encrypted block and {@code 0}
* skip blocks be used with HLS SAMPLE-AES audio. This will trigger decryption to use cbcs mode
* while still decrypting every block.
*/
public final static class CryptoInfo {
/**
@@ -2377,11 +2421,13 @@ final public class MediaCodec {
*/
public int numSubSamples;
/**
* The number of leading unencrypted bytes in each subSample.
* The number of leading unencrypted bytes in each subSample. If null, all bytes are treated
* as encrypted and {@link #numBytesOfEncryptedData} must be specified.
*/
public int[] numBytesOfClearData;
/**
* The number of trailing encrypted bytes in each subSample.
* The number of trailing encrypted bytes in each subSample. If null, all bytes are treated
* as clear and {@link #numBytesOfClearData} must be specified.
*/
public int[] numBytesOfEncryptedData;
/**
@@ -2400,35 +2446,34 @@ final public class MediaCodec {
public int mode;
/**
* Metadata describing an encryption pattern for the protected bytes in
* a subsample. An encryption pattern consists of a repeating sequence
* of crypto blocks comprised of a number of encrypted blocks followed
* by a number of unencrypted, or skipped, blocks.
* Metadata describing an encryption pattern for the protected bytes in a subsample. An
* encryption pattern consists of a repeating sequence of crypto blocks comprised of a
* number of encrypted blocks followed by a number of unencrypted, or skipped, blocks.
*/
public final static class Pattern {
/**
* Number of blocks to be encrypted in the pattern. If zero, pattern
* encryption is inoperative.
* Number of blocks to be encrypted in the pattern. If both this and
* {@link #mSkipBlocks} are zero, pattern encryption is inoperative.
*/
private int mEncryptBlocks;
/**
* Number of blocks to be skipped (left clear) in the pattern. If zero,
* pattern encryption is inoperative.
* Number of blocks to be skipped (left clear) in the pattern. If both this and
* {@link #mEncryptBlocks} are zero, pattern encryption is inoperative.
*/
private int mSkipBlocks;
/**
* Construct a sample encryption pattern given the number of blocks to
* encrypt and skip in the pattern.
* Construct a sample encryption pattern given the number of blocks to encrypt and skip
* in the pattern. If both parameters are zero, pattern encryption is inoperative.
*/
public Pattern(int blocksToEncrypt, int blocksToSkip) {
set(blocksToEncrypt, blocksToSkip);
}
/**
* Set the number of blocks to encrypt and skip in a sample encryption
* pattern.
* Set the number of blocks to encrypt and skip in a sample encryption pattern. If both
* parameters are zero, pattern encryption is inoperative.
*/
public void set(int blocksToEncrypt, int blocksToSkip) {
mEncryptBlocks = blocksToEncrypt;