[FFmpeg-devel] [PATCH 1/5] avcodec/h264_mp4toannexb_bsf: refactor start_code_size handling

[Zhao Zhili <quinkblack@foxmail.com>]

From: Zhao Zhili <zhilizhao@tencent.com>

start_code_size depends on whether PS comes from out-of-band or
in-band. Make the code more readable.
---
 libavcodec/h264_mp4toannexb_bsf.c | 34 ++++++++++++++++++++++++-------
 1 file changed, 27 insertions(+), 7 deletions(-)

diff --git a/libavcodec/h264_mp4toannexb_bsf.c b/libavcodec/h264_mp4toannexb_bsf.c
index d11be455c2..7dce1ae9b6 100644
--- a/libavcodec/h264_mp4toannexb_bsf.c
+++ b/libavcodec/h264_mp4toannexb_bsf.c
@@ -43,10 +43,26 @@ typedef struct H264BSFContext {
     int      extradata_parsed;
 } H264BSFContext;
 
+enum PsSource {
+    PS_OUT_OF_BAND = -1,
+    PS_NONE = 0,
+    PS_IN_BAND = 1,
+};
+
 static void count_or_copy(uint8_t **out, uint64_t *out_size,
-                          const uint8_t *in, int in_size, int ps, int copy)
+                          const uint8_t *in, int in_size, enum PsSource ps, int copy)
 {
-    uint8_t start_code_size = ps < 0 ? 0 : *out_size == 0 || ps ? 4 : 3;
+    uint8_t start_code_size;
+
+    if (ps == PS_OUT_OF_BAND)
+        /* start code already present in out-of-band ps data, so don't need to
+         * add it manually again
+         */
+        start_code_size = 0;
+    else if (ps == PS_IN_BAND || *out_size == 0)
+        start_code_size = 4;
+    else
+        start_code_size = 3;
 
     if (copy) {
         memcpy(*out + start_code_size, in, in_size);
@@ -202,6 +218,7 @@ static int h264_mp4toannexb_filter(AVBSFContext *ctx, AVPacket *opkt)
 
         do {
             uint32_t nal_size = 0;
+            enum PsSource ps;
 
             /* possible overread ok due to padding */
             for (int i = 0; i < s->length_size; i++)
@@ -230,7 +247,7 @@ static int h264_mp4toannexb_filter(AVBSFContext *ctx, AVPacket *opkt)
                     if (!s->sps_size) {
                         LOG_ONCE(ctx, AV_LOG_WARNING, "SPS not present in the stream, nor in AVCC, stream may be unreadable\n");
                     } else {
-                        count_or_copy(&out, &out_size, s->sps, s->sps_size, -1, j);
+                        count_or_copy(&out, &out_size, s->sps, s->sps_size, PS_OUT_OF_BAND, j);
                         sps_seen = 1;
                     }
                 }
@@ -246,19 +263,22 @@ static int h264_mp4toannexb_filter(AVBSFContext *ctx, AVPacket *opkt)
             if (new_idr && unit_type == H264_NAL_IDR_SLICE && !sps_seen && !pps_seen) {
                 if (ctx->par_out->extradata)
                     count_or_copy(&out, &out_size, ctx->par_out->extradata,
-                                  ctx->par_out->extradata_size, -1, j);
+                                  ctx->par_out->extradata_size, PS_OUT_OF_BAND, j);
                 new_idr = 0;
             /* if only SPS has been seen, also insert PPS */
             } else if (new_idr && unit_type == H264_NAL_IDR_SLICE && sps_seen && !pps_seen) {
                 if (!s->pps_size) {
                     LOG_ONCE(ctx, AV_LOG_WARNING, "PPS not present in the stream, nor in AVCC, stream may be unreadable\n");
                 } else {
-                    count_or_copy(&out, &out_size, s->pps, s->pps_size, -1, j);
+                    count_or_copy(&out, &out_size, s->pps, s->pps_size, PS_OUT_OF_BAND, j);
                 }
             }
 
-            count_or_copy(&out, &out_size, buf, nal_size,
-                          unit_type == H264_NAL_SPS || unit_type == H264_NAL_PPS, j);
+            if (unit_type == H264_NAL_SPS || unit_type == H264_NAL_PPS)
+                ps = PS_IN_BAND;
+            else
+                ps = PS_NONE;
+            count_or_copy(&out, &out_size, buf, nal_size, ps, j);
             if (!new_idr && unit_type == H264_NAL_SLICE) {
                 new_idr  = 1;
                 sps_seen = 0;
-- 
2.25.1

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