tinycap: support streaming captured PCM to stdout

It is sometimes useful for testing to be able to stream the
captured PCM to another tool instead of being forced to save
it to a WAV file.

Using '--' instead of the target filename will send the raw
PCM to stdout (without any header).

Signed-off-by: Richard Fitzgerald <rf@opensource.wolfsonmicro.com>

1 files changed, 30 insertions, 13 deletions

diff --git a/tinycap.c b/tinycap.c
index 7429750..b9ae251 100644
--- a/tinycap.c
+++ b/tinycap.c
@@ -57,6 +57,7 @@ struct wav_header {
 };
 
 int capturing = 1;
+int prinfo = 1;
 
 unsigned int capture_sample(FILE *file, unsigned int card, unsigned int device,
                             unsigned int channels, unsigned int rate,
@@ -81,17 +82,25 @@ int main(int argc, char **argv)
     unsigned int period_size = 1024;
     unsigned int period_count = 4;
     enum pcm_format format;
+    int no_header = 0;
 
     if (argc < 2) {
-        fprintf(stderr, "Usage: %s file.wav [-D card] [-d device] [-c channels] "
-                "[-r rate] [-b bits] [-p period_size] [-n n_periods]\n", argv[0]);
+        fprintf(stderr, "Usage: %s {file.wav | --} [-D card] [-d device] [-c channels] "
+                "[-r rate] [-b bits] [-p period_size] [-n n_periods]\n\n"
+                "Use -- for filename to send raw PCM to stdout\n", argv[0]);
         return 1;
     }
 
-    file = fopen(argv[1], "wb");
-    if (!file) {
-        fprintf(stderr, "Unable to create file '%s'\n", argv[1]);
-        return 1;
+    if (strcmp(argv[1],"--") == 0) {
+        file = stdout;
+        prinfo = 0;
+        no_header = 1;
+    } else {
+        file = fopen(argv[1], "wb");
+        if (!file) {
+            fprintf(stderr, "Unable to create file '%s'\n", argv[1]);
+            return 1;
+        }
     }
 
     /* parse command line arguments */
@@ -160,20 +169,26 @@ int main(int argc, char **argv)
     header.data_id = ID_DATA;
 
     /* leave enough room for header */
-    fseek(file, sizeof(struct wav_header), SEEK_SET);
+    if (!no_header) {
+        fseek(file, sizeof(struct wav_header), SEEK_SET);
+    }
 
     /* install signal handler and begin capturing */
     signal(SIGINT, sigint_handler);
     frames = capture_sample(file, card, device, header.num_channels,
                             header.sample_rate, format,
                             period_size, period_count);
-    printf("Captured %d frames\n", frames);
+    if (prinfo) {
+        printf("Captured %d frames\n", frames);
+    }
 
     /* write header now all information is known */
-    header.data_sz = frames * header.block_align;
-    header.riff_sz = header.data_sz + sizeof(header) - 8;
-    fseek(file, 0, SEEK_SET);
-    fwrite(&header, sizeof(struct wav_header), 1, file);
+    if (!no_header) {
+        header.data_sz = frames * header.block_align;
+        header.riff_sz = header.data_sz + sizeof(header) - 8;
+        fseek(file, 0, SEEK_SET);
+        fwrite(&header, sizeof(struct wav_header), 1, file);
+    }
 
     fclose(file);
 
@@ -216,8 +231,10 @@ unsigned int capture_sample(FILE *file, unsigned int card, unsigned int device,
         return 0;
     }
 
-    printf("Capturing sample: %u ch, %u hz, %u bit\n", channels, rate,
+    if (prinfo) {
+        printf("Capturing sample: %u ch, %u hz, %u bit\n", channels, rate,
            pcm_format_to_bits(format));
+    }
 
     while (capturing && !pcm_read(pcm, buffer, size)) {
         if (fwrite(buffer, 1, size, file) != size) {