lavu/tx: improve documentation

libavutil/tx.h

@@ -40,11 +40,17 @@ enum AVTXType {
     /**
      * Standard complex to complex FFT with sample data type AVComplexFloat.
      * Output is not 1/len normalized. Scaling currently unsupported.
+     * The stride parameter is ignored.
      */
     AV_TX_FLOAT_FFT = 0,
     /**
      * Standard MDCT with sample data type of float and a scale type of
      * float. Length is the frame size, not the window size (which is 2x frame)
+     * For forward transforms, the stride specifies the spacing between each
+     * sample in the output array in bytes. The input must be a flat array.
+     * For inverse transforms, the stride specifies the spacing between each
+     * sample in the input array in bytes. The output will be a flat array.
+     * Stride must be a non-zero multiple of sizeof(float).
      */
     AV_TX_FLOAT_MDCT = 1,
     /**
@@ -53,6 +59,7 @@ enum AVTXType {
     AV_TX_DOUBLE_FFT = 2,
     /**
      * Same as AV_TX_FLOAT_MDCT with data and scale type of double.
+     * Stride must be a non-zero multiple of sizeof(double).
      */
     AV_TX_DOUBLE_MDCT = 3,
     /**
@@ -62,6 +69,7 @@ enum AVTXType {
     /**
      * Same as AV_TX_FLOAT_MDCT with data type of int32_t and scale type of float.
      * Only scale values less than or equal to 1.0 are supported.
+     * Stride must be a non-zero multiple of sizeof(int32_t).
      */
     AV_TX_INT32_MDCT = 5,
 };
@@ -75,8 +83,11 @@ enum AVTXType {
  * @param s the transform context
  * @param out the output array
  * @param in the input array
- * @param stride the input or output stride (depending on transform direction)
- * in bytes, currently implemented for all MDCT transforms
+ * @param stride the input or output stride in bytes
+ *
+ * The out and in arrays must be aligned to the maximum required by the CPU
+ * architecture.
+ * The stride must follow the constraints the transform type has specified.
  */
 typedef void (*av_tx_fn)(AVTXContext *s, void *out, void *in, ptrdiff_t stride);