avformat/avienc: add muxer option "write_channel_mask"

Allow writing an empty channel mask into the wave format header. Useful
if the input file contains an unknown channel layout.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/avienc.c

@@ -34,6 +34,7 @@
 #include "libavutil/dict.h"
 #include "libavutil/avassert.h"
 #include "libavutil/timestamp.h"
+#include "libavutil/opt.h"
 #include "libavutil/pixdesc.h"
 #include "libavcodec/raw.h"
 
@@ -58,9 +59,11 @@ typedef struct AVIIndex {
 } AVIIndex;
 
 typedef struct AVIContext {
+    const AVClass *class;
     int64_t riff_start, movi_list, odml_list;
     int64_t frames_hdr_all;
     int riff_id;
+    int write_channel_mask;
 } AVIContext;
 
 typedef struct AVIStream {
@@ -339,7 +342,7 @@ static int avi_write_header(AVFormatContext *s)
         ff_end_tag(pb, strh);
 
         if (enc->codec_type != AVMEDIA_TYPE_DATA) {
-            int ret;
+            int ret, flags;
             enum AVPixelFormat pix_fmt;
 
             strf = ff_start_tag(pb, "strf");
@@ -367,7 +370,8 @@ static int avi_write_header(AVFormatContext *s)
                           av_get_pix_fmt_name(enc->pix_fmt));
                 break;
             case AVMEDIA_TYPE_AUDIO:
-                if ((ret = ff_put_wav_header(pb, enc, 0)) < 0)
+                flags = (avi->write_channel_mask == 0) ? FF_PUT_WAV_HEADER_SKIP_CHANNELMASK : 0;
+                if ((ret = ff_put_wav_header(pb, enc, flags)) < 0)
                     return ret;
                 break;
             default:
@@ -782,6 +786,20 @@ static int avi_write_trailer(AVFormatContext *s)
     return res;
 }
 
+#define OFFSET(x) offsetof(AVIContext, x)
+#define ENC AV_OPT_FLAG_ENCODING_PARAM
+static const AVOption options[] = {
+    { "write_channel_mask", "write channel mask into wave format header", OFFSET(write_channel_mask), AV_OPT_TYPE_BOOL, { .i64 = 1 }, 0, 1, ENC },
+    { NULL },
+};
+
+static const AVClass avi_muxer_class = {
+    .class_name = "AVI muxer",
+    .item_name  = av_default_item_name,
+    .option     = options,
+    .version    = LIBAVUTIL_VERSION_INT,
+};
+
 AVOutputFormat ff_avi_muxer = {
     .name           = "avi",
     .long_name      = NULL_IF_CONFIG_SMALL("AVI (Audio Video Interleaved)"),
@@ -796,4 +814,5 @@ AVOutputFormat ff_avi_muxer = {
     .codec_tag      = (const AVCodecTag * const []) {
         ff_codec_bmp_tags, ff_codec_wav_tags, 0
     },
+    .priv_class     = &avi_muxer_class,
 };

libavformat/riff.h

@@ -52,6 +52,11 @@ void ff_put_bmp_header(AVIOContext *pb, AVCodecContext *enc, const AVCodecTag *t
  */
 #define FF_PUT_WAV_HEADER_FORCE_WAVEFORMATEX    0x00000001
 
+/**
+ * Tell ff_put_wav_header() to write an empty channel mask.
+ */
+#define FF_PUT_WAV_HEADER_SKIP_CHANNELMASK      0x00000002
+
 /**
  * Write WAVEFORMAT header structure.
  *

libavformat/riffenc.c

@@ -168,8 +168,9 @@ int ff_put_wav_header(AVIOContext *pb, AVCodecContext *enc, int flags)
     }
     /* write WAVEFORMATEXTENSIBLE extensions */
     if (waveformatextensible) {
-        int write_channel_mask = enc->strict_std_compliance < FF_COMPLIANCE_NORMAL ||
-                                 enc->channel_layout < 0x40000;
+        int write_channel_mask = !(flags & FF_PUT_WAV_HEADER_SKIP_CHANNELMASK) &&
+                                 (enc->strict_std_compliance < FF_COMPLIANCE_NORMAL ||
+                                  enc->channel_layout < 0x40000);
         /* 22 is WAVEFORMATEXTENSIBLE size */
         avio_wl16(pb, riff_extradata - riff_extradata_start + 22);
         /* ValidBitsPerSample || SamplesPerBlock || Reserved */