[FFmpeg-devel] [PATCH] Use av_log() to log messages from the libopenh264 encoder.

[Gregory J. Wolfe]

File libopenh264enc.c has been modified so that the encoder uses av_log()
to log messages (error, warning, info, etc.) instead of logging them
directly to stderr.  At the time the encoder is created, the current
libav log level is mapped to an equivalent libopenh264 log level.  This
log level, and a message logging function that invokes av_log() to
actually log messages, are then set on the encoder.

Signed-off-by: Gregory J. Wolfe <gregory.wolfe at kodakalaris.com>
---
 libavcodec/libopenh264enc.c | 90 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)

diff --git a/libavcodec/libopenh264enc.c b/libavcodec/libopenh264enc.c
index 55554ae..44ad251 100644
--- a/libavcodec/libopenh264enc.c
+++ b/libavcodec/libopenh264enc.c
@@ -59,6 +59,72 @@ static const AVClass class = {
     "libopenh264enc", av_default_item_name, options, LIBAVUTIL_VERSION_INT
 };
 
+// Convert libav log level to equivalent libopenh264 log level.  Given the
+// conversions below, you must set the libav log level to something greater
+// than AV_LOG_DEBUG if you want to see WELS_LOG_DETAIL messages.
+static int libav_to_libopenh264_log_level  (
+    int libav_log_level
+    )
+{
+    int equiv_libopenh264_log_level;
+    if  ( libav_log_level > AV_LOG_DEBUG )
+        equiv_libopenh264_log_level = WELS_LOG_DETAIL;   // > AV_LOG_DEBUG; this is EXTREMELY detailed
+    else if  ( libav_log_level >= AV_LOG_DEBUG )
+        equiv_libopenh264_log_level = WELS_LOG_DEBUG;    // AV_LOG_DEBUG
+    else if  ( libav_log_level >= AV_LOG_INFO )
+        equiv_libopenh264_log_level = WELS_LOG_INFO;     // AV_LOG_INFO, AV_LOG_VERBOSE
+    else if  ( libav_log_level >= AV_LOG_WARNING )
+        equiv_libopenh264_log_level = WELS_LOG_WARNING;  // AV_LOG_WARNING
+    else if  ( libav_log_level >= AV_LOG_ERROR )
+        equiv_libopenh264_log_level = WELS_LOG_ERROR;    // AV_LOG_ERROR
+    else
+        equiv_libopenh264_log_level = WELS_LOG_QUIET;    // AV_LOG_QUIET, AV_LOG_PANIC, AV_LOG_FATAL
+    return equiv_libopenh264_log_level;
+}
+
+// Convert libopenh264 log level to equivalent libav log level.
+static int libopenh264_to_libav_log_level  (
+    int libopenh264_log_level
+    )
+{
+    int equiv_libav_log_level;
+    if  ( libopenh264_log_level >= WELS_LOG_DETAIL )
+        equiv_libav_log_level = AV_LOG_DEBUG + 1;           // WELS_LOG_DETAIL
+    else if  ( libopenh264_log_level >= WELS_LOG_DEBUG )
+        equiv_libav_log_level = AV_LOG_DEBUG;               // WELS_LOG_DEBUG
+    else if  ( libopenh264_log_level >= WELS_LOG_INFO )
+        equiv_libav_log_level = AV_LOG_INFO;                // WELS_LOG_INFO
+    else if  ( libopenh264_log_level >= WELS_LOG_WARNING )
+        equiv_libav_log_level = AV_LOG_WARNING;             // WELS_LOG_WARNING
+    else if  ( libopenh264_log_level >= WELS_LOG_ERROR )
+        equiv_libav_log_level = AV_LOG_ERROR;               // WELS_LOG_ERROR
+    else
+        equiv_libav_log_level = AV_LOG_QUIET;               // WELS_LOG_QUIET
+    return equiv_libav_log_level;
+}
+
+// This function will be provided to the libopenh264 library.  The function will be called
+// when libopenh264 wants to log a message (error, warning, info, etc.).  The signature for
+// this function (defined in .../codec/api/svc/codec_api.h) is:
+//
+//        typedef void (*WelsTraceCallback) (void* ctx, int level, const char* string);
+
+static void libopenh264_trace_callback  (
+    void *          ctx,
+    int             level,
+    char const *    msg
+    )
+{
+    // The message will be logged only if the requested EQUIVALENT libav log level is
+    // less than or equal to the current libav log level.  Note, however, that before
+    // this function is called, welsCodecTrace::CodecTrace() will have already discarded
+    // the message (and this function will not be called) if the requested libopenh264
+    // log level "level" is greater than the current libopenh264 log level.
+    int equiv_libav_log_level = libopenh264_to_libav_log_level(level);
+    if  ( equiv_libav_log_level <= av_log_get_level() )
+        av_log((AVCodecContext *) ctx, equiv_libav_log_level, "%s\n", msg);
+}
+
 static av_cold int svc_encode_close(AVCodecContext *avctx)
 {
     SVCContext *s = avctx->priv_data;
@@ -73,6 +139,8 @@ static av_cold int svc_encode_init(AVCodecContext *avctx)
     SVCContext *s = avctx->priv_data;
     SEncParamExt param = { 0 };
     int err = AVERROR_UNKNOWN;
+    int equiv_libopenh264_log_level;
+    WelsTraceCallback callback_function;
 
     // Mingw GCC < 4.7 on x86_32 uses an incorrect/buggy ABI for the WelsGetCodecVersion
     // function (for functions returning larger structs), thus skip the check in those
@@ -90,6 +158,28 @@ static av_cold int svc_encode_init(AVCodecContext *avctx)
         return AVERROR_UNKNOWN;
     }
 
+    // Set libopenh264 message logging level for this instance of the encoder using
+    // the current libav log level converted to the equivalent libopenh264 level.
+    //
+    // The client should have the libav level set to the desired value before creating
+    // the libopenh264 encoder.  Once the encoder has been created, the libopenh264
+    // log level is fixed for that encoder.  Changing the libav log level to a LOWER
+    // value, in the expectation that higher level libopenh264 messages will no longer
+    // be logged, WILL have the expected effect.  However, changing the libav log level
+    // to a HIGHER value, in the expectation that higher level libopenh264 messages will
+    // now be logged, WILL NOT have the expected effect.  This is because the higher
+    // level messages will be discarded by the libopenh264 logging system before our
+    // message logging callback function can be invoked.
+    equiv_libopenh264_log_level = libav_to_libopenh264_log_level(av_log_get_level());
+    (*s->encoder)->SetOption(s->encoder,ENCODER_OPTION_TRACE_LEVEL,&equiv_libopenh264_log_level);
+
+    // Set the logging callback function to one that uses av_log() (see implementation above).
+    callback_function = (WelsTraceCallback) libopenh264_trace_callback;
+    (*s->encoder)->SetOption(s->encoder,ENCODER_OPTION_TRACE_CALLBACK,(void *)&callback_function);
+
+    // Set the AVCodecContext as the libopenh264 callback context so that it can be passed to av_log().
+    (*s->encoder)->SetOption(s->encoder,ENCODER_OPTION_TRACE_CALLBACK_CONTEXT,(void *)&avctx);
+
     (*s->encoder)->GetDefaultParams(s->encoder, &param);
 
     param.fMaxFrameRate              = 1/av_q2d(avctx->time_base);
-- 
2.5.1.windows.1