[FFmpeg-devel] [PATCH 20/25] fftools/ffmpeg_filter: simplify choose_pix_fmts

[Niklas Haas]

From: Niklas Haas <git at haasn.dev>

The only meaningful difference between choose_pix_fmts and the default
code was the inclusion of an extra branch for `keep_pix_fmt` being true.

However, in this case, we either:
1. Force the specific `ofp->format` that we inherited from
   ofilter_bind_ost, or if no format was set:
2. Print an empty format list

Both of these goals can be accomplished by simply moving the decision
logic to ofilter_bind_ost, to avoid setting any format list when
keep_pix_fmt is enabled. This is arguably cleaner as it moves format
selection logic to a single function. In the case of branch 1, nothing
else needs to be done as we already force the format provided in
ofp->format, if any is set. Add an assertion to verify this assumption
just in case.

(Side note: The "choose_*" family of functions are arguably misnomers,
as they should really be called "print_*" - their current behavior is to
print the relevant format lists to the `vf/af_format` filter arguments)
---
 fftools/ffmpeg_filter.c | 49 ++++++++---------------------------------
 1 file changed, 9 insertions(+), 40 deletions(-)

diff --git a/fftools/ffmpeg_filter.c b/fftools/ffmpeg_filter.c
index dd5cfe4481..5b99c4ba40 100644
--- a/fftools/ffmpeg_filter.c
+++ b/fftools/ffmpeg_filter.c
@@ -313,36 +313,6 @@ static void sub2video_update(InputFilterPriv *ifp, int64_t heartbeat_pts,
     ifp->sub2video.initialize = 0;
 }
 
-/* *dst may return be set to NULL (no pixel format found), a static string or a
- * string backed by the bprint. Nothing has been written to the AVBPrint in case
- * NULL is returned. The AVBPrint provided should be clean. */
-static int choose_pix_fmts(OutputFilter *ofilter, AVBPrint *bprint,
-                           const char **dst)
-{
-    OutputFilterPriv *ofp = ofp_from_ofilter(ofilter);
-    OutputStream *ost = ofilter->ost;
-
-    *dst = NULL;
-
-    if (ost->keep_pix_fmt || ofp->format != AV_PIX_FMT_NONE) {
-        *dst = ofp->format == AV_PIX_FMT_NONE ? NULL :
-               av_get_pix_fmt_name(ofp->format);
-    } else if (ofp->formats) {
-        const enum AVPixelFormat *p = ofp->formats;
-
-        for (; *p != AV_PIX_FMT_NONE; p++) {
-            const char *name = av_get_pix_fmt_name(*p);
-            av_bprintf(bprint, "%s%c", name, p[1] == AV_PIX_FMT_NONE ? '\0' : '|');
-        }
-        if (!av_bprint_is_complete(bprint))
-            return AVERROR(ENOMEM);
-
-        *dst = bprint->str;
-    }
-
-    return 0;
-}
-
 /* Define a function for appending a list of allowed formats
  * to an AVBPrint. If nonempty, the list will have a header. */
 #define DEF_CHOOSE_FORMAT(name, type, var, supported_list, none, printf_format, get_name) \
@@ -365,8 +335,8 @@ static void choose_ ## name (OutputFilterPriv *ofp, AVBPrint *bprint)          \
     av_bprint_chars(bprint, ':', 1);                                           \
 }
 
-//DEF_CHOOSE_FORMAT(pix_fmts, enum AVPixelFormat, format, formats, AV_PIX_FMT_NONE,
-//                  GET_PIX_FMT_NAME)
+DEF_CHOOSE_FORMAT(pix_fmts, enum AVPixelFormat, format, formats,
+                  AV_PIX_FMT_NONE, "%s", av_get_pix_fmt_name)
 
 DEF_CHOOSE_FORMAT(sample_fmts, enum AVSampleFormat, format, formats,
                   AV_SAMPLE_FMT_NONE, "%s", av_get_sample_fmt_name)
@@ -690,7 +660,7 @@ int ofilter_bind_ost(OutputFilter *ofilter, OutputStream *ost)
         ofp->height     = ost->enc_ctx->height;
         if (ost->enc_ctx->pix_fmt != AV_PIX_FMT_NONE) {
             ofp->format = ost->enc_ctx->pix_fmt;
-        } else {
+        } else if (!ost->keep_pix_fmt) {
             ofp->formats = c->pix_fmts;
 
             // MJPEG encoder exports a full list of supported pixel formats,
@@ -1169,7 +1139,6 @@ static int configure_output_video_filter(FilterGraph *fg, OutputFilter *ofilter,
     AVBPrint bprint;
     int pad_idx = out->pad_idx;
     int ret;
-    const char *pix_fmts;
     char name[255];
 
     snprintf(name, sizeof(name), "out_%d_%d", ost->file_index, ost->index);
@@ -1204,17 +1173,17 @@ static int configure_output_video_filter(FilterGraph *fg, OutputFilter *ofilter,
         pad_idx = 0;
     }
 
+    av_assert0(!ost->keep_pix_fmt || (!ofp->format && !ofp->formats));
     av_bprint_init(&bprint, 0, AV_BPRINT_SIZE_UNLIMITED);
-    ret = choose_pix_fmts(ofilter, &bprint, &pix_fmts);
-    if (ret < 0)
-        return ret;
-
-    if (pix_fmts) {
+    choose_pix_fmts(ofp, &bprint);
+    if (!av_bprint_is_complete(&bprint))
+        return AVERROR(ENOMEM);
+    if (bprint.len) {
         AVFilterContext *filter;
 
         ret = avfilter_graph_create_filter(&filter,
                                            avfilter_get_by_name("format"),
-                                           "format", pix_fmts, NULL, fg->graph);
+                                           "format", bprint.str, NULL, fg->graph);
         av_bprint_finalize(&bprint, NULL);
         if (ret < 0)
             return ret;
-- 
2.42.0